title:
Non-gaussian CMB temperature fluctuations from peculiar velocities of
  clusters

abstract:
  We use numerical simulations of a (480 Mpc/h)^3 volume to show that the
distribution of peak heights in maps of the temperature fluctuations from the
kinematic and thermal Sunyaev-Zeldovich effects will be highly non-Gaussian,
and very different from the peak height distribution of a Gaussian random
field. We then show that it is a good approximation to assume that each peak in
either SZ effect is associated with one and only one dark matter halo. This
allows us to use our knowledge of the properties of haloes to estimate the peak
height distributions. At fixed optical depth, the distribution of peak heights
due to the kinematic effect is Gaussian, with a width which is approximately
proportional to optical depth; the non-Gaussianity comes from summing over a
range of optical depths. The optical depth is an increasing function of halo
mass, and the distribution of halo speeds is Gaussian, with a dispersion which
is approximately independent of halo mass. This means that observations of the
kinematic effect can be used to put constraints on how the abundance of massive
clusters evolves, and on the evolution of cluster velocities. The
non-Gaussianity of the thermal effect, on the other hand, comes primarily from
the fact that, on average, the effect is larger in more massive haloes, and the
distribution of halo masses is highly non-Gaussian. We also show that because
haloes of the same mass may have a range of density and velocity dispersion
profiles, the relation between halo mass and the amplitude of the thermal
effect is not deterministic, but has some scatter.


title: Ultraluminous X-Ray Sources in External Galaxies

abstract:
  We investigate models for the class of ultraluminous non-nuclear X-ray
sources (ULXs) seen in a number of galaxies and probably associated with
star-forming regions. Models where the X-ray emission is assumed to be
isotropic run into several difficulties. In particular formation of sufficient
numbers of the required ultramassive black-hole X-ray binaries is problematic,
and the likely transient behaviour of the resulting systems is not in good
accord with observation. The assumption of mild X-ray beaming suggests instead
that ULXs may represent a shortlived but extremely common stage in the
evolution of a wide class of X-ray binaries. The best candidate for this is the
phase of thermal-timescale mass transfer inevitable in many intermediate and
high-mass X-ray binaries. This in turn suggests a link with the Galactic
microquasars. The short lifetimes of high-mass X-ray binaries would explain the
association of ULXs with episodes of star formation. These considerations still
allow the possibility that individual ULXs may contain extremely massive black
holes.


title:
Environment status of blue compact galaxies and trigger of star
  formation

abstract:
  (abridged) The work studies active star formation (SF) and a possible trigger
of SF bursts due to gravitational interaction. Following the study by Taylor et
al. we extend the search for possible disturbing galaxies of various masses to
a much larger sample of 86 BCGs from the sky region of Second Byurakan survey.
The sample under study is separated by the criteria: EW([O III]5007 > 45 A and
V < 6,000 km/s and should be representative of all low-mass galaxies which
experience SF bursts. We argue that the moderate tidal disturbers should be
taken into account, and incorporate the respective range of distances in the
search for disturbing neighbours. The majority of the neighbours in the
vicinity of the studied BCGs are found through the study of their environment
among UZC galaxies, and the follow-up careful search of the fainter galaxies in
the NED database. For the remaining BCGs, the neighbouring galaxies are found
based on the results of the 6-m telescope spectroscopy. By studing the data on
the radial velocities of galaxies in the vicinity of BCGs we found: 1) 33 of
the studied BCGs (38.5 %) are associated with significantly brighter galaxies
(DB > 1.5 mag); 2) 23 BCGs (26.5%) have neighbours either of comparable or
significantly lower brightness; 3) 14 of the studied BCGs (16%) with no evident
associated galaxy are either certain, or probable, mergers. We conclude that in
\~80% (or more) BCGs from the studied sample, the SF bursts are triggered
either by tidal action of various strengths from other galaxies, or due to
mergers of low-mass galaxies. We briefly discuss the implications of our main
conclusion for evolutionary links of BCGs to other types of low-mass galaxies.
Among the ``isolated'' BCGs (without a bright neighbour) 43+-10% are probably
disturbed by dwarf galaxies and 26+-8% have a merger morphology.


title:
Tuning the Clock: Uranium and Thorium Chronometers Applied to CS
  31082-001

abstract:
  We obtain age estimates for the progenitor(s) of the extremely metal-poor
([Fe/H = -2.9) halo star CS 31082-001, based on the recently reported first
observation of a Uranium abundance in this (or any other) star. Age estimates
are derived by application of the classical r-process model with updated
nuclear physics inputs. The [U/Th] ratio yields an age of 13+-4 Gyr or 8+-4
Gyr, based on the use of the ETFSI-Q or the new HFBCS-1 nuclear mass models,
respectively. Implications for Thorium chronometers are discussed.


title: Planets in 47 Tuc

abstract:
  We consider the survivability of planetary systems in the globular cluster 47
Tucanae. We compute the cross sections for the breakup of planetary systems via
encounters with single stars and binaries. We also compute the cross sections
to leave planets on eccentric orbits. We find that wider planetary systems (d >
0.3 AU) are likely to be broken up in the central regions of 47 Tucanae (within
the half-mass radius of the cluster). However tighter systems, and those in
less-dense regions may survive. Tight systems will certainly survive in
less-dense clusters where subsequent surveys should be conducted.


title: Back to the subseismic approximation for core undertones

abstract:
  The problem of the long-period gravity modes of the Earth outer fluid core is
investigated using either the subseismic or the anelastic approximation These
two approximations aim at filtering out the uninteresting short-period seismic
or acoustic oscillations while taking into account the density variations
across the core However, they differ on the form of the equation of mass
conservation since the density perturbations do not contribute to the mass
balance in the anelastic case Here we show that these two approximations lead
to the almost same results because of the weakness of the core stratification
due to the convective mixing The anelastic approximation should be however
preferred because it is simpler, mathematically self-consistent and is the only
one which can be applied to problems with a stronger stratification such as the
ones encountered in radiative zones of stars


title: TANGO ARRAY An Air Shower Experiment in Buenos Aires

abstract:
  A new Air Shower Observatory has been constructed in Buenos Aires during
1999, and commissioned and set in operation in 2000. The observatory consists
of an array of four water \v{C}erenkov detectors, enclosing a geometrical area
of $\sim$ 30.000 m$^{2}$, and is optimized for the observation of cosmic rays
in the ``knee'' energy region. The array detects $\sim$ 250 to $\sim$ 1500
showers/day, depending on the selected triggering condition. In this paper, the
design and construction of the array, and the automatic system for data
adquisition, daily calibration, and monitoring, are described. Also, the Monte
Carlo simulations performed to develop a shower database, as well as the
studies performed using the database to estimate the response and the angular
and energy resolutions of the array, are presented in detail.


title: On the Nature of the Residual Magnetic Fields in Millisecond Pulsars

abstract:
  We consider the expulsion of proton fluxoids along neutron vortices from the
superfluid/superconductive core of neutron star with weak ($B<10^{10}$ G)
magnetic field. The velocity of fluxoids is calculated from the balance of
buoyancy, drag and crustal forces. We show, that the proton fluxoids can leave
the superfluid core sliding {\it along} the neutron vortices on a timescale of
about $10^7$ years. An alternative possibility is that fluxoids are aligned
with the vortices on the same timescale. As the result, non--aligned surface
magnetic fields of millisecond pulsars can be sustained for $\ga 10^9$ years
only in case of a comparable dissipation timescale of the currents in the
neutron star crust. This defines upper limits of the impurity concentration in
the neutron star crust: $Q \la 0.1$ if a stiff equation of state determines the
density profile.


title: VIIZw 403: a BCD with a noncoeval starburst

abstract:
  The recent history of star formation in VIIZw 403 is analyzed taking into
account the dynamics of the starburst blown superbubble and the restrictions
that follow from X-ray observations, and from our H$\alpha$ data. Our results
show that the starburst energizing VIIZw 403 is NOT coeval, but rather the star
forming phase has lasted for more than 30Myr and at such a low pace that most
probably the newly processed metals will not be ejected into the intergalactic
medium.


title:
Morphology of Circumstellar Environment and Some Characterictics of
  Circumstellar Shells of Stars with the R Coronae Borealis Variability

abstract:
  The well-known light minima of stars with the R Coronae Borealis variability
are caused by the formation of an additional circumstellar dust shell, the
screening shell, inside the permanent shell. Under the assumption of uniform
distribution of matter in the circumstellar environment we estimated the
optical thickness of the permanent gas-and-dust shell at 0.2-0.7, and its
geometrical thickness is no less than 0.4 of its own radius. The wavelength
dependence of extinction is close to neutral. From spectral observations of R
CrB itself in the 1985 minimum we traced the transformation of the stellar
linear and molecular absorption spectrum to the emission spectrum and
established that the fast variation of the U-B colour index by -0.6 in the
light decline was caused purely by a change of the spectrum type. The spectrum
transformation causes an increase of star brightness in the U, B, and V bands
by about 1.4, 0.75, and 0.75 mags, correspondingly. It is suggested that a
high-velocity (>200 km/s) matter stream through the circumstellar environment
is the cause of the excitation of the emissions observed during light minima
when the photospheric flux is weakening.


title: Relativistic ionized accretion disc models of MCG--6-30-15

abstract:
  We present results from fitting ionized accretion disc models to three long
ASCA observations of the Seyfert 1 galaxy MCG--6-30-15. All three datasets can
be fit by a model consisting of ionized reflection from the inner region of the
accretion disc (with twice solar Fe abundance) and a separate diskline
component from farther out on the the disc. The diskline is required to fit the
height of the observed Fe K line profile. However, we show that a much simpler
model of reflection from a very weakly ionized constant density disc also fits
the data. In this case only a single cold Fe K line at 6.4 keV is required to
fit the observed line. The ionized disc models predict that O VIII K, C VI K,
Fe XVII L, and Fe XVIII L lines will appear in the soft X-ray region of the
reflection spectrum, but are greatly blurred due to Compton scattering. The
equivalent width (EW) of O VIII K is estimated to be about 10 eV and seems to
be as strong as the blend of the Fe L lines. This result creates difficulty for
the claim of a strong relativistic O VIII line in the XMM-Newton grating
spectrum of MCG--6-30-15, although we can not strictly rule it out since
MCG--6-30-15 was in an anomalously low state during that observation. We find
that increasing the O abundance or breaking the continuum below 2 keV will not
significantly strengthen the line. The second Fe K line component in the
ionized disc model may arise from neutral reflection from a flared disc, or
from a second illumination event. The data cannot distinguish between the two
cases, and we conclude that single zone ionized disc models have difficulty
fitting these hard X-ray data of MCG--6-30-15.


title: A Study of the Unidentified Gamma-Ray Source 3EG J1828+0142

abstract:
  We present a study of the radio environment of the gamma-ray source 3EG
J1828+0142. This source presents a very high variability index in its gamma
emission and a steep high-energy spectral index $\Gamma\sim-2.8$. Large-scale
radio maps at different frequencies show the presence of a shell-type
non-thermal structure when the diffuse emission from the Galactic disk is
eliminated. At small scales, VLA radio images reveal the existence of several
weak point sources within the 95 % gamma-ray confidence location contour. Most
of these sources present non-thermal spectral indices, but it is not clear
whether they are extragalactic or not. We discuss the possibility of a scenario
where the large structure is a SNR and one of the compact radio sources is an
isolated black hole also produced in the original supernova explosion. The
black hole could be responsible for the variable gamma-ray emission according
to Punsly's (1998) model. INTEGRAL observations with IBIS imager could detect
the inverse Compton and blueshifted pair annihilation radiation from the
relativistic electron-positron jets of the hole. Some estimates are presented
in this regard.


title:
H110alpha recombination-line emission and 4.8-GHz continuum emission in
  the Carina Nebula

abstract:
  We present results from observations of H110alpha recombination-line emission
at 4.874 GHz and the related 4.8-GHz continuum emission towards the Carina
Nebula using the Australia Telescope Compact Array. These data provide
information on the velocity, morphology and excitation parameters of the
ionized gas associated with the two bright HII regions within the nebula, Car I
and Car II. They are consistent with both Car I and Car II being expanding
ionization fronts arising from the massive star clusters Trumpler 14 and
Trumpler 16, respectively. The overall continuum emission distribution at 4.8
GHz is similar to that at lower frequencies. For Car I, two compact sources are
revealed that are likely to be young HII regions associated with triggered star
formation. These results provide the first evidence of ongoing star formation
in the northern region of the nebula. A close association between Car I and the
molecular gas is consistent with a scenario in which Car I is currently carving
out a cavity within the northern molecular cloud. The complicated kinematics
associated with Car II point to expansion from at least two different centres.
All that is left of the molecular cloud in this region are clumps of dense gas
and dust which are likely to be responsible for shaping the striking morphology
of the Car II components.


title: Dust emission from the lensed Lyman break galaxy cB58

abstract:
  We detect 1.2mm continuum emission from dust in the gravitationally lensed
Lyman break galaxy MS 1512+36-cB58. Our detected flux is surprisingly low:
relative to local starburst galaxies, cB58 appears to produce somewhat less
far-IR emission than its UV reddening predicts. After comparing several
different estimates of the source's dust content, we conclude that the apparent
discrepancy is most likely related to uncertainty in its UV spectral slope.
Alternate scenarios to account for a far-IR "deficit" which rely on a high dust
temperature or differential magnification are less satisfactory. Our result
underscores one of the risks inherent in characterizing the cosmic star
formation history from rest-UV data alone.


title:
Modeling the spectral energy distribution of galaxies. II. Disk opacity
  and star formation in 5 edge-on spirals

abstract:
  Using tools previously described and applied to the prototype galaxy NGC 891,
we model the optical to far-infrared spectral energy distributions (SED) of
four additional edge-on spiral galaxies, namely NGC 5907, NGC 4013, UGC 1082
and UGC 2048. Comparing the model predictions with IRAS and, where available,
sub-millimeter and millimeter observations, we determine the respective roles
of the old and young stellar populations in grain heating. In all cases, the
young population dominates, with the contribution of the old stellar population
being at most 40%, as previously found for NGC 891. After normalization to the
disk area, the massive star-formation rate (SFR) derived using our SED modeling
technique, which is primarily sensitive to the non-ionizing ultraviolet output
from the young stellar population, lies in the range 7e-4 - 2e-2 M_sun * yr^-1
* kpc^-2. This is consistent with normalized SFRs derived for face-on galaxies
of comparable surface gas densities from H_alpha observations. Though the most
active star-forming galaxy of the five in absolute terms, NGC 891 is not an
exceptional system in terms of its surface density in SFR.


title: Disk Frequencies and Lifetimes in Young Clusters

abstract:
  We report the results of the first sensitive L-band (3.5 micron) survey of
the intermediate age (2.5 - 30 Myr) clusters NGC 2264, NGC 2362 and NGC 1960.
We use JHKL colors to obtain a census of the circumstellar disk fractions in
each cluster. We find disk fractions of 52% +/- 10%, 12% +/- 4% and 3% +/- 3%
for the three clusters respectively. Together with our previously published
JHKL investigations of the younger NGC 2024, Trapezium and IC 348 clusters, we
have completed the first systematic and homogenous survey for circumstellar
disks in a sample of young clusters that both span a significant range in age
(0.3 - 30 Myr) and contain statistically significant numbers of stars whose
masses span nearly the entire stellar mass spectrum. Analysis of the combined
survey indicates that the cluster disk fraction is initially very high (> 80%)
and rapidly decreases with increasing cluster age, such that half the stars
within the clusters lose their disks in < ~3 Myr. Moreover, these observations
yield an overall disk lifetime of ~ 6 Myr in the surveyed cluster sample. This
is the timescale for essentially all the stars in a cluster to lose their
disks. This should set a meaningful constraint for the planet building
timescale in stellar clusters. The implications of these results for current
theories of planet formation are briefly discussed.


title:
Guiding the Way to Gamma-Ray Sources: X-ray Studies of Supernova
  Remnants

abstract:
  Supernova remnants have long been suggested as a class of potential
counterparts to unidentified gamma-ray sources. The mechanisms by which such
gamma-rays can arise may include emission from a pulsar associated with a
remnant, or a variety of processes associated with energetic particles
accelerated by the SNR shock. Imaging and spectral observations in the X-ray
band can be used to identify properties of the remnants that lead to gamma-ray
emission, including the presence of pulsar-driven nebulae, nonthermal X-ray
emission from the SNR shells, and the interaction of SNRs with dense
surrounding material.


title:
Solutions to the tethered galaxy problem in an expanding universe and
  the observation of receding blueshifted objects

abstract:
  We use the dynamics of a galaxy, set up initially at a constant proper
distance from an observer, to derive and illustrate two counter-intuitive
general relativistic results. Although the galaxy does gradually join the
expansion of the universe (Hubble flow), it does not necessarily recede from
us. In particular, in the currently favored cosmological model, which includes
a cosmological constant, the galaxy recedes from the observer as it joins the
Hubble flow, but in the previously favored cold dark matter model, the galaxy
approaches, passes through the observer, and joins the Hubble flow on the
opposite side of the sky. We show that this behavior is consistent with the
general relativistic idea that space is expanding and is determined by the
acceleration of the expansion of the universe -- not a force or drag associated
with the expansion itself. We also show that objects at a constant proper
distance will have a nonzero redshift; receding galaxies can be blueshifted and
approaching galaxies can be redshifted.


title: Study of star formation in RCW 106 using far infrared observations

abstract:
  High resolution far-infrared observations of a large area of the star forming
complex RCW 106 obtained using the TIFR 1-metre balloon-borne telescope are
presented. Intensity maps have been obtained simultaneously in two bands
centred around 150 & 210 micron. Intensity maps have also been obtained at the
4 IRAS bands using HIRES processed IRAS data. From the 150 & 210 micron maps,
reliable maps of dust temperature and optical depth have been generated. The
star formation in this complex has occured in five linear subclumps. Using the
map at 210 micron, which has a spatial resolution superior to that of the IRAS
at 100 micron, 23 sources have been identified. The SED and luminosity of these
sources have been determined using the associations wit hthe IRAS maps.
Luminosity distribution of these sources has been obtained. Assuming these
embedded sources to be ZAMS stars and using the mass-luminosity relation, the
power law slope of the Initial Mass Function is found to be -1.73+-0.5. This
index for this very young complex is about the same as that for more evolved
complexes and clusters. Radiation transfer calculations in spherical geometry
have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR
and IRAS bands. From this, the r^-2 density distribution in the envelopes is
ruled out. Finally, a correlation is seen between the luminosity of embedded
sources and the computed dust masses of the envelopes.


title:
On the time variability of gamma-ray sources: A numerical analysis of
  variability indices

abstract:
  We present a Monte Carlo analysis of the recently introduced variability
indices $\tau$ (Tompkins 1999) and $I$ (Zhang et al. 2000 & Torres et al. 2001)
for $\gamma$-ray sources. We explore different variability criteria and prove
that these two indices, despite the very different approaches used to compute
them, are statistically correlated (5 to 7$\sigma$). This conclusion is
maintained also for the subset of AGNs and high latitude ($|b|>10$ deg)
sources, whereas the correlation is lowered for the low latitude ones, where
the influence of the diffuse galactic emission background is strong.


title: The Nature of the Emission Components in the Quasar/NLS1 PG1211+143

abstract:
  We present the study of the emission properties of the quasar PG1211+143,
which belongs to the class of Narrow Line Seyfert 1 galaxies. On the basis of
observational data analyzed by us and collected from the literature, we study
the temporal and spectral variability of the source in the optical/UV/X-ray
bands and we propose a model that explains the spectrum emitted in this broad
energy range. In this model, the intrinsic emission originating in the warm
skin of the accretion disk is responsible for the spectral component that is
dominant in the softest X-ray range. The shape of reflected spectrum as well as
Fe K line detected in hard X-rays require the reflecting medium to be mildly
ionized (xi~500). We identify this reflector with the warm skin of the disk and
we show that the heating of the skin is consistent with the classical alpha
P_{tot} prescription, while alpha P_{gas} option is at least two orders of
magnitude too low to provide the required heating. We find that the mass of the
central black hole is relatively small (M_BH~10^7- 10^8 Msun, which is
consistent with the Broad Line Region mapping results and characteristic for
NLS1 class.


title: Nonthermal X-Ray Emission from G266.2-1.2 (RX J0852.0-4622)

abstract:
  The newly discovered supernova remnant G266.2-1.2 (RX J0852.0-4622), along
the line of sight to the Vela SNR, was observed with ASCA for 120 ks. We find
that the X-ray spectrum is featureless, and well described by a power law,
extending to three the class of shell-type SNRs dominated by nonthermal X-ray
emission. Although the presence of the Vela SNR compromises our ability to
accurately determine the column density, the GIS data appear to indicate
absorption considerably in excess of that for Vela itself, indicating that
G266.2-1.2 may be several times more distant. An unresolved central source may
be an associated neutron star, though difficulties with this interpretation
persist.


title: Mesogranulation and Turbulence in Photospheric Flows

abstract:
  Below the scale of supergranules we find that cellular flows are present in
the solar photosphere at two distinct size scales, approximately 2 Mm and 4 Mm,
with distinct characteristic times. Simultaneously present in the flow is a
non-cellular component, with turbulent scaling properties and containing 30% of
the flow energy. These results are obtained by means of wavelet spectral
analysis and modeling of vertical photospheric motions in a 2-hour sequence of
120 SOHO/MDI, high resolution, Doppler images near disk center. The wavelets
permit detection of specific local flow patterns corresponding to convection
cells.


title: Distance to the Active Galaxy NGC 6951 via the Type Ia Supernova 2000E

abstract:
  CCD-photometry and low-resolution spectroscopy of the bright supernova SN
2000E in NGC 6951 are presented. Both the light curve extending up to 150 days
past maximum and the spectra obtained at 1 month past maximum confirm that SN
2000E is of Type Ia. The reddening of SN 2000E is determined as
E(B-V)=0.36+/-0.15, its error is mainly due to uncertainties in the predicted
SN (B-V) colour at late epochs. The V(RI)_C light curves are analyzed with the
Multi-Colour Light Curve Shape (MLCS) method. The shape of the late light curve
suggests that SN 2000E was overluminous by about 0.5 mag at maximum comparing
with a fiducial SN Ia. This results in an updated distance of 33+/-8 Mpc of NGC
6951 (corrected for interstellar absorption). The SN-based distance modulus is
larger by about +0.7 mag than the previous Tully-Fisher estimates. However,
possible systematic errors due to ambiguities in the reddening determination
and estimates of the maximum luminosity of SN 2000E may plague the present
distance measurement.


title: Discovery of an X-ray pulsar in the low-mass X-ray binary 2A 1822-371

abstract:
  We report the discovery of 0.59 s X-ray pulsations from the low-mass X-ray
binary, 5.57 hr dipping and eclipsing ADC source 2A 1822-371. Pulse arrival
time analysis indicates a circular orbit with e < 0.03 (95% confidence) and an
asini for the neutron star of 1.006(5) lightseconds, implying a mass function
of (2.03+-0.03) x 10^-2 M_sun. The barycentric pulse period was 0.59325(2) s in
1996.270 and 0.59308615(5) s in 1998.205, indicating an average spin up with
P_dot/P = (-1.52+-0.02) x 10^-4 yr^-1. For a magnetic field strength of ~1--5 x
10^12 G as derived from the X-ray spectrum the implied intrinsic X-ray
luminosity is ~2-4 x 10^37 erg s^-1. The pulse amplitude is low, but increases
steeply as a function of energy from a sinusoidal amplitude of 0.25% in 2-5.4
keV to ~3% above 20 keV. We discuss the constraints on the masses of the
companion star and the fact that several aspects of the energy spectrum are in
qualitative accordance with that of a strongly magnetised neutron star.


title: Measurement of stellar age from uranium decay

abstract:
  The ages of the oldest stars in the Galaxy indicate when star formation
began, and provide a minimum age for the Universe. Radioactive dating of
meteoritic material and stars relies on comparing the present abundance ratios
of radioactive and stable nuclear species to the theoretically predicted ratios
of their production. The radioisotope $^{232}$Th (half-life 14 Gyr) has been
used to date Galactic stars, but it decays by only a factor of two over the
lifetime of the Universe. $^{238}$U (half-life 4.5 Gyr) is in principle a more
precise age indicator, but even its strongest spectral line, from singly
ionized uranium at a wavelength of 385.957 nm, has previously not been detected
in stars. Here we report a measurement of this line in the very metal-poor star
CS31082-001, a star which is strongly overabundant in its heavy elements. The
derived uranium abundance, log(U/H) = -13.7+/-0.14+/-0.12 yields an age of
12.5+/-3 Gyr, though this is still model dependent. The observation of this
cosmochronometer gives the most direct age determination of the Galaxy. Also,
with improved theoretical and laboratory data, it will provide a highly precise
lower limit to the age of the Universe.


title: Tidally-induced Super Star Clusters in M82

abstract:
  Using new HST imaging, we identify a large, evolved system of super star
clusters in a disk region just outside the starburst core in the prototypical
starburst galaxy M82, ``M82 B.'' This region has been suspected to be a fossil
starburst site in which an intense episode of star formation occurred over 100
Myr ago, which is now confirmed by our derived age distribution. It suggests
steady, continuing cluster formation at a modest rate at early times (> 2 Gyr
ago), followed by a concentrated formation episode ~600 Myr ago and more recent
suppression of cluster formation. The peak episode coincides with independent
dynamical estimates for the last tidal encounter with M81.


title: Hope and Inquietudes in Nucleo-cosmochronology

abstract:
  Critical views are presented on some nucleo-cosmochronological questions.
Progress has been made recently in the development of the 187Re-187Os
cosmochronometry. From this, there is good hope for this clock to become of the
highest quality for the nuclear dating of the Universe. The simultaneous
observation of Th and U in ultra-metal-poor stars would also be a most
interesting prospect. In contrast, a serious inquietude is expressed about the
reliability of the chronometric attempts based on the classical 232Th-238U and
235U-238U pairs, as well as on the Th (without U) abundance determinations in
ultra-metal poor stars.


title:
Spectra of Maser Radiation from a Turbulent, Circumnuclear Accretion
  Disk. III. Circular polarization

abstract:
  Calculations are performed for the circular polarization of maser radiation
from a turbulent, Keplerian disk that is intended to represent the sub-parsec
disk at the nucleus of the galaxy NGC4258. The polarization in the calculations
is a result of the Zeeman effect in the regime in which the Zeeman splitting is
much less than the spectral linebreadth. Plausible configurations for turbulent
magnetic and velocity fields in the disk are created by statistical methods.
This turbulence, along with the Keplerian velocity gradients and the blending
of the three hyperfine components to form the $6_{16} - 5_{23}$ masing
transition of water, are key ingredients in determining the appearance of the
polarized spectra that are calculated. These spectra are quite different from
the polarized spectra that would be expected for a two-level transition where
there is no hyperfine structure. The effect of the hyperfine structure on the
polarization is most striking in the calculations for the maser emission that
represents the central (or systemic) features of NGC4258. Information about
magnetic fields is inferred from observations for polarized maser radiation and
bears on the structure of accretion disks.


title:
Nonlinear Stochastic Biasing of Galaxies and Dark Halos in Cosmological
  Hydrodynamic Simulations

abstract:
  We perform an extensive analysis of nonlinear and stochastic biasing of
galaxies and dark halos in spatially flat low-density CDM universe using
cosmological hydrodynamic simulations. We compare their biasing properties with
the predictions of an analytic halo biasing model. Dark halos in our
simulations exhibit reasonable agreement with the predictions only on scales
larger than 10h^{-1}Mpc, and on smaller scales the volume exclusion effect of
halos due to their finite size becomes substantial. Interestingly the biasing
properties of galaxies are better described by extrapolating the halo biasing
model predictions.
  We also find the clear dependence of galaxy biasing on their formation epoch;
the distribution of old populations of galaxies tightly correlates with the
underlying mass density field, while that of young populations is slightly more
stochastic and anti-biased relative to dark matter. The amplitude of two-point
correlation function of old populations is about 3 times larger than that of
the young populations. Furthermore, the old population of galaxies reside
within massive dark halos while the young galaxies are preferentially formed in
smaller dark halos. Assuming that the observed early and late-type galaxies
correspond to the simulated old and young populations of galaxies,
respectively, all of these segregations of galaxies are consistent with
observational ones for the early and late-type of galaxies such as the
morphology--density relation of galaxies.


title: BeppoSAX measurements of the bright gamma-ray burst 010222

abstract:
  We analyze the BeppoSAX measurements of the prompt and afterglow emission of
the gamma-ray burst GRB010222. Among 45 GRBs detected with the Wide Field
Cameras on BeppoSAX, the 40-700 keV fluence of (9.3+/-0.3)E-5 erg cm-2 is only
surpassed by GRB990123. In terms of the isotropic 20-2000 keV energy output of
7.8E53 erg, it ranks third of all GRBs with measured distances. Since this
burst is so bright, the data provide complete and valuable coverage up to 65 hr
after the event, except for a gap between 3.5 and 8.0 hr. The 2-10 keV flux
history shows clear signs of a break which is consistent with a break seen in
the optical, and provides supporting evidence for the achromatic nature of the
break. An explanation for the break in the context of a collimated expansion is
not straightforward. Rather, a model is favored whereby the fireball is braked
to the non-relativistic regime quickly (within a fraction of day) by a dense
1E6 cm-3 circumburst medium. This implies that, after a mild beaming
correction, GRB010222 may be the most energetic burst observed thus far. The
X-ray decay index after the break is 1.33+/-0.04, the spectral index
0.97+/-0.05. The decay is, with unprecedented accuracy, identical to that
observed in the optical.


title: Optical Photometry of the GRB 010222 Afterglow

abstract:
  The optical afterglow of GRB 010222 was observed using the recently installed
2-m telescope at the Indian Astronomical Observatory, Hanle, and the telescopes
at the Vainu Bappu Observatory, Kavalur, beginning ~ 0.6 day after the
detection of the event. The results based on these photometric observations
combined with others reported in the literature are presented in this paper.
The R band light curve shows an initial decline of intensities proportional to
t^{-0.542} which steepens, after 10.3 hours, to t^{-1.263}. Following the model
of collimated outflow, the early break in the light curve implies a very narrow
beam angle (~ 2-3 deg). The two decay rates are consistent with the standard
jet model in a uniform density ambient medium, but require a hard spectrum of
electron power density with p ~ 1.5. The R band light between 14 and 17 hours
since outburst departs from the power law fit by 0.1 mag and shows some
evidence for fluctuations over timescales of an hour in the observer's frame.
Such deviations are expected due to density inhomogeneities if the ambient
medium is similar to the local interstellar medium. GRB 010222 is thus an
example of a highly collimated outflow with a hard spectrum of electron energy
distribution in normal interstellar environment.


title: Carbon Recombination Lines from the Galactic Plane at 34.5 & 328 MHz

abstract:
  We present results of a search for carbon recombination lines in the Galaxy
at 34.5 MHz (C$575\alpha$) made using the dipole array at Gauribidanur near
Bangalore. Observations made towards 32 directions, led to detections of lines
in absorption at nine positions. Followup observations at 328 MHz
(C$272\alpha$) using the Ooty Radio Telescope detected these lines in emission.
A VLA D-array observation of one of the positions at 330 MHz yielded no
detection implying a lower limit of 10' for the angular size of the line
forming region.
  The longitude-velocity distribution of the observed carbon lines indicate
that the line forming region are located mainly between 4 kpc and 7 kpc from
the Galactic centre. Combining our results with published carbon recombination
line data near 76 MHz (\nocite{erickson:95} Erickson \et 1995) we obtain
constraints on the physical parameters of the line forming regions. We find
that if the angular size of the line forming regions is $\ge 4^{\circ}$, then
the range of parameters that fit the data are: \Te $= 20-40$ K, \ne $\sim
0.1-0.3$ \cm3 and pathlengths $\sim 0.07-0.9$ pc which may correspond to thin
photo-dissociated regions around molecular clouds. On the other hand, if the
line forming regions are $\sim 2^{\circ}$ in extent, then warmer gas (\Te $\sim
60-300$ K) with lower electron densities (\ne $\sim 0.03-0.05$ \cm3) extending
over several tens of parsecs along the line of sight and possibly associated
with atomic \HI gas can fit the data. Based on the range of derived parameters,
we suggest that the carbon line regions are most likely associated with
photo-dissociation regions.


title: Space-VLBI phase-reference mapping and astrometry

abstract:
  We present 5 GHz space-VLBI observations of the quasar pair
B1342+662/B1342+663 that demonstrate the feasibility of phase-reference
techniques using an antenna in space. The space-based data were taken by the
satellite HALCA, of the space-VLBI mission VSOP. From residual (referenced)
phases we derive an upper bound of 10 meters to the uncertainty of the
spacecraft orbit reconstruction. An analysis of the phase-reference maps of the
sources additionally suggests that the above mentioned uncertaintyis likely not
larger than 3 meters. With errors of this magnitude, HALCA is a useful tool for
astrometric studies of close pairs of radio sources.


title: Concerning Parameter Estimation Using the Cosmic Microwave Background

abstract:
  Most parameter constraints obtained from cosmic microwave background (CMB)
anisotropy data are based on power estimates and rely on approximate likelihood
functions; computational difficulties generally preclude an exact analysis
based on pixel values. With the specific goal of testing this kind of approach,
we have performed a complete (un-approximated) likelihood analysis combining
the COBE, Saskatoon and MAX data sets. We examine in detail the ability of
certain approximate techniques based on band-power estimates to recover the
full likelihood constraints. The traditional $\chi^2$-method does not always
find the same best-fit model as the likelihood analysis (a bias), due mainly to
the false assumption of Gaussian likelihoods that makes the method overly
sensitive to data outliers. Although an improvement, other approaches employing
non-Gaussian flat-band likelihoods do not always faithfully reproduce the
complete likelihood constraints either; not even when using the exact flat-band
likelihood curves. We trace this to the neglect of spectral information by
simple flat band-power estimates. A straightforward extension incorporating a
local effective slope (of the power spectrum, $C_l$) provides a faithful
representation of the likelihood surfaces without significantly increasing
computing cost. Finally, we also demonstrate that the best-fit model to this
particular data set is a {\em good fit}, or that the observations are
consistent with Gaussian sky fluctuations, according to our statistic.


title:
The 0.1-100 keV Spectrum of LMC X-4 in the High State: Evidence for a
  High Energy Cyclotron Absorption Line

abstract:
  We report on the spectral analysis of the X-ray pulsar LMC X-4 in its high
state out of eclipse observed by BeppoSAX. During this observation no coherent
pulsations are detected. The primary continuum is well described by a power law
with a high energy cutoff (E_cutoff ~ E_fold ~ 18 keV). The addition of a
cyclotron absorption line at ~100 keV improves the fit significantly. The
inferred magnetic moment is 1.1 10^{31} Gauss cm^3, in agreement with the value
estimated assuming that the neutron star is at the spin equilibrium, as it has
been proposed for this source. The remaining excess at low energies can be
fitted by a Comptonization of soft photons by moderately hot electrons (kT ~0.9
keV), with an optical depth \tau ~ 16. The seed photons for this Comptonization
are consistent with black body emission from the accretion disk at the
magnetospheric radius. Another possibility is to fit the soft excess with black
body and thermal bremsstrahlung. In this case the black body would originate
from cold plasma at the magnetosphere while the bremsstrahlung component may be
produced by the strong stellar wind from the companion star, ionized by the
X-ray emission from the pulsar.


title: The Extrgalactic Gamma-Ray Background

abstract:
  The COMPTEL and EGRET detectors aboard the Compton Gamma-Ray Observatory
measured an extragalactic gamma-ray background extending from MeV energies up
to about 100 GeV. Calculations performed making reasonable assumptions indicate
that blazars can account for the background between about 10 MeV and at least
10 GeV. Below 30 MeV, the background flux and spectrum are not very well
determined and a dedicated satellite detector will be required to remedy this
situation. Below 10 MeV, supernovae and possibly AGN may contribute to the
extragalactic background flux. Above 10 GeV, the role of blazars in
contributing to the background is unclear because we do not have data on their
spectra at these energies and because theoretical models predict that many of
them will have spectra which should cut off in this energy range. At these
higher energies, a new component, perhaps from topological defects, may
contribute to the background, as well as X-ray selected BL Lac objects. The
future GLAST detector should provide important data on the emission of
extragalactic sources above 10 GeV and help resolve this issue. GLAST may also
be able to detect the signature of intergalactic absorption by pair production
interactions of background gamma-rays of energy above 20 GeV with starlight
photons, this signature being a steepening of the background spectrum.


title:
Optimization of grazing incidence mirrors and its application to
  surveying X-ray telescopes

abstract:
  Grazing incidence mirrors for X-ray astronomy are usually designed in the
parabola-hyperbola (Wolter I) configuration. This design allows for optimal
images on-axis, which however degrade rapidly with the off-axis angle. Mirror
surfaces described by polynomia (with terms higher than order two), have been
put forward to improve the performances over the field of view. Here we present
a refined procedure aimed at optimizing wide-field grazing incidence telescopes
for X-ray astronomy. We improve the angular resolution over existing
(wide-field) designs by ~ 20%. We further consider the corrections for the
different plate scale and focal plane curvature of the mirror shells, which
sharpen by another ~ 20% the image quality. This results in a factor of ~ 2
reduction in the observing time needed to achieve the same sensitivity over
existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate
that such wide-field X-ray telescopes are highly advantageous for deep surveys
of the X-ray sky.


title: From Fractal Cosmography to Fractal Cosmology

abstract:
  Assuming a fractal distribution of matter in the universe, consequences that
follow from the General Theory of Relativity and the Copernican Principle for
fractal cosmology are examined. The change in perspective necessary to deal
with a fractal universe is highlighted. An ansatz that provides a concrete
application of the Conditional Cosmological Principle is provided. This fractal
cosmology is obtained by arguments closely following those used in standard
cosmology. The resulting model may play a significant role in the debate on
whether the universe is a fractal or crosses over to homogeneity at some scale.
This model may also be regarded as an idealized fractal model around which more
realistic models may be built.


title: Testing Quintessence models with large-scale structure growth

abstract:
  We explore the possibility of putting constraints on quintessence models with
large-scale structure observations. In particular we compute the linear and
second order growth rate of the fluctuations in different flavors of
quintessence scenarios. We show that effective models of quintessence (e.g.
with a constant equation of state) do not account of the results found in more
realistic scenarios.
  The impact of these results on observational quantities such as the shape of
the non-linear power spectrum in weak lensing surveys or the skewness of the
convergence field are investigated. It appears that the observational signature
of quintessence models are specific and rather large. They clearly cannot be
mistaken with a change of (\Omega_{0}).


title: Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes

abstract:
  The radio components associated with the LMXB Sco X-1 have been monitored
with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a
56-hour continuous VLBI observation in 1999 June. We often detected one strong
and one weak compact radio component, moving in opposite directions from the
radio core. We suggest that the moving components are radio lobes generated by
the disruption of energy flow in a twin-beam from the binary system. The
average lifetime of a lobe-pair, the space motion of the lobes and the measured
energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a
flux density that is variable over a time-scale of one hour, a measured minimum
size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short
electron radiative lifetime may be caused by synchrotron losses if the lobe
magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as
they are produced at the working surface. The lobes also show periods of slow
expansion and a steepening radio spectrum, perhaps related to the
characteristics of the beam energy flow. The radio morphology for Sco X-1 is
more simple than for most other Galactic jet sources. The lobes of Sco X-1 are
similar to hot-spots found in many extragalactic double sources. Scaling the
phenomena observed in Sco X-1 to extragalactic sources implies hot-spot
variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The
recurrent formation of lobes in Sco X-1 probably does not occur for
extragalactic radio sources.


title: Hydrodynamical Simulations of Jet- and Wind-driven Protostellar Outflows

abstract:
  We present two-dimensional hydrodynamical simulations of both jet- and
wind-driven models for protostellar outflows in order to make detailed
comparisons to the kinematics of observed molecular outflows.
  Comparing the different simulations with observations, we find that some
outflows, e.g., HH 212, show features consistent with the jet-driven model,
while others, e.g., VLA 05487, are consistent with the wind-driven model.


title: A ballistic bow shock model for jet-driven protostellar outflow shells

abstract:
  We analyze the dynamics of the shell produced when a bow shock from a
collimated jet propagates into the surrounding medium. Under interstellar
conditions, the shock is radiative, and a ballistic approximation for the shell
flow is appropriate beyond the working surface where the jet impacts its
surroundings. The solution is then determined by the ambient and jet densities
and velocities and by the momentum impulse applied in the working surface.
Using estimates for these impulses (confirmed by separate numerical
simulations), we obtain solutions for the shell structure, and for the range of
velocities in the shell at any point. We provide predictions for the
position-velocity and mass-velocity relations expected for plane-of-sky
bow-shock shells, and for the bulk shell properties. In a companion paper, we
show that these analytic solutions are in excellent agreement with the results
of direct numerical simulations. We argue that classical molecular (CO)
outflows cannot be purely jet-driven, because the bow-shock shell solutions are
much too elongated compared with observations. Finally, we suggest that the
``spur'' structures seen in position-velocity diagrams of observed molecular
outflows are the manifestation of internal bow shocks which may be fit with our
simple dynamical models.


title:
FUSE Detection of Diffuse Galactic O VI Emission toward the Coma and
  Virgo Clusters

abstract:
  We report the detection of diffuse O VI 1032, 1038 A emission in a 29-ksec
observation centered on the Coma Cluster (l = 57.6, b = +88.0) and an 11-ksec
observation toward Virgo (l = 284.2, b = +74.5) through the low-resolution
(30"x30") aperture of the Far Ultraviolet Spectroscopic Explorer (FUSE). The
emission lines have a redshift near zero and are thus produced by gas in our
own Galaxy. Observed surface brightnesses are 2000 +/- 600 photons/cm2/s/sr for
each of the O VI components in the Coma spectrum and 2900 +/- 700 and 1700 +/-
700 photons/cm2/s/sr for the 1032 and 1038 A lines, respectively, toward Virgo.
These features are similar in strength to those recently observed in the
southern Galactic hemisphere (l = 315.0, b =-41.3) in an ~ 200 ksec FUSE
observation. From a FUSE spectrum of M87, we find that N(O VI) toward Virgo is
(1.4 +/- 0.8) x 10^14 cm^{-2}. By combining emission- and absorption-line data
for this sight line, we estimate the physical parameters of the emitting gas.


title: The Radio Corona of AR Lacertae

abstract:
  We present multifrequency VLA and VLBA observations at 8.4 GHz of the RS CVn
system AR Lac, that were performed in autumn 1997 simultaneously with X-ray
observations obtained from Rodono` et al. (1999). Our VLBA data indicate a
resolved source with dimension close to the system separation, while the study
of the flux density curve evidences a small amplitude outside of the eclipse
variability. The derived five-frequencies spectra, combined with the size
information from VLBA data, are compared with gyrosynchrotron emission from a
two component structured source. A comparison with the results of the X-ray
observations allow us to exclude the possibility that thermal gyrosynchrotron
is responsible for the radio emission, but it is compatible with the hypothesis
of co-spatial X-ray and radio emitting sources.


title:
Photometric Variability in the Ultracool Dwarf BRI 0021-0214: Possible
  Evidence for Dust Clouds

abstract:
  We report CCD photometric monitoring of the nonemission ultracool dwarf BRI
0021-0214 (M9.5) obtained during 10 nights in 1995 November and 4 nights in
1996 August, with CCD cameras at 1 m class telescopes on the observatories of
the Canary Islands. We present differential photometry of BRI 0021-0214, and we
report significant variability in the I-band light curve obtained in 1995. A
periodogram analysis finds a strong peak at a period of 0.84 day. This
modulation appears to be transient because it is present in the 1995 data but
not in the 1996 data. We also find a possible period of 0.20 day, which appears
to be present in both the 1995 and 1996 datasets. However, we do not find any
periodicity close to the rotation period expected from the spectroscopic
rotational broadening (< 0.14 day). BRI 0021-0214 is a very inactive object,
with extremely low levels of Halpha and X-ray emission. Thus, it is unlikely
that magnetically induced cool spots can account for the photometric
variability. The photometric variability of BRI 0021-0214 could be explained by
the presence of an active meteorology that leads to inhomogeneous clouds on the
surface. The lack of photometric modulation at the expected rotational period
suggests that the pattern of surface features may be more complicated than
previously anticipated.


title:
Spectral differences between the radio-loud and radio-quiet low-hard
  states of GRS 1915+105: possible detection of synchrotron radiation in X-rays

abstract:
  The Galactic microquasar GRS 1915+105 exhibits several episodes of steady
X-ray emission characterized by a hard power-law spectrum and intense Quasi
Periodic Oscillations. It is known that there are two types of such low-hard
states, one with steady radio emission and the other without any significant
radio emission. We present the results of a detailed X-ray spectroscopic study
of GRS 1915+105, using data from the Rossi X-ray Timing Explorer obtained
during various episodes of the low-hard states of the source. We show that
there are distinct X-ray spectral differences between the radio-quiet and
radio-loud low-hard states of the source. The X-ray spectra of the radio-quiet
low-hard state is best described by a model consisting ofa multicolor
disk-blackbody and a Comptonized component, whereas the X-ray spectra of
radio-loud low-hard state requires a model consisting of three components: a
multicolor disk-blackbody, a Comptonized component and a power-law, for
statistically and physically acceptable fits. We attempt to model the presence
of this additional power-law component as due to synchrotronradiation which is
responsible for the radio and infrared radiation from thesource. We show that a
simple adiabatically expanding jet model for the synchrotron radiation can
account for the observed X-ray flux for reasonable values of the magnetic field
and the mass outflow rate. This is the first report of detection of the
synchrotron radiation in the X-ray band for this source.


title:
Fine-Tuning Solution for Hybrid Inflation in Dissipative Chaotic
  Dynamics

abstract:
  We study the presence of chaotic behavior in phase space in the
pre-inflationary stage of hybrid inflation models. This is closely related to
the problem of initial conditions associated to these inflationary type of
models. We then show how an expected dissipative dynamics of fields just before
the onset of inflation can solve or ease considerably the problem of initial
conditions, driving naturally the system towards inflation. The chaotic
behavior of the corresponding dynamical system is studied by the computation of
the fractal dimension of the boundary, in phase space, separating inflationary
from non-inflationary trajectories. The fractal dimension for this boundary is
determined as a function of the dissipation coefficients appearing in the
effective equations of motion for the fields.


title:
Supermassive Black Holes in Active Galactic Nuclei. I. The Consistency
  of Black Hole Masses in Quiescent and Active Galaxies

abstract:
  We report the first results of a program to measure accurate stellar velocity
dispersions in the bulges of the host galaxies of active galactic nuclei (AGNs)
for which accurate black hole (BH) masses have been determined via
reverberation mapping. We find good agreement between BH masses obtained from
reverberation mapping, and from the M(BH) - sigma relation as defined by
quiescent galaxies, indicating a common relationship between active and
quiescent black holes and their large-scale environments.


title:
X-raying Active Galaxies with the New Generation of X-ray Observatories:
  Ionized Outflows and High-Redshift Studies

abstract:
  We briefly review X-ray studies of ionized AGN outflows and high-redshift
AGN. We discuss recent progress with Chandra and XMM-Newton as well as
prospects and requirements for future X-ray missions.


title:
Timescale Stretch Parameterization of Type Ia Supernova B-band Light
  Curves

abstract:
  R-band intensity measurements along the light curve of Type Ia supernovae
discovered by the Supernova Cosmology Project (SCP) are fitted in brightness to
templates allowing a free parameter the time-axis width factor w = s(1+z). The
data points are then individually aligned in the time-axis, normalized and
K-corrected back to the rest frame, after which the nearly 1300 normalized
intensity measurements are found to lie on a well-determined common rest-frame
B-band curve which we call the ``composite curve''. The same procedure is
applied to 18 low-redshift Calan/Tololo SNe with z < 0.11; these nearly 300
B-band photometry points are found to lie on the composite curve equally well.
The SCP search technique produces several measurements before maximum light for
each supernova. We demonstrate that the linear stretch factor, s, which
parameterizes the light-curve timescale appears independent of z,and applies
equally well to the declining and rising parts of the light curve. In fact, the
B-band template that best fits this composite curve fits the individual
supernova photometry data when stretched by a factor s with chi^2/DoF approx =
1, thus as well as any parameterization can, given the current data sets. The
measurement of the date of explosion, however, is model dependent and not
tightly constrained by the current data.
  We also demonstrate the 1+z light-curve time-axis broadening expected from
cosmological expansion. This argues strongly against alternative explanations,
such as tired light, for the redshift of distant objects.


title: On the masses of black-holes in radio-loud quasars

abstract:
  The central black-hole masses of a sample of radio-loud quasars are estimated
by using the data of $H_{\beta}$ line-width and the optical continuum
luminosity. The vast majority of the quasars in this sample have black-hole
masses larger than $10^{8} M_{\odot}$, while a few quasars may contain
relatively smaller black-holes. We found a significant anti-correlation between
the radio-loudness and the central black-hole mass. It might imply that the jet
formation is governed by the black-hole mass.


title:
A high frequency radio study of G11.2-0.3, a historical supernova
  remnant with a flat spectrum core

abstract:
  We present radio maps of the historical supernova remnant G11.2-0.3 in the
frequency range from 4.85 GHz to 32 GHz. The integrated spectrum with \alpha =
-0.50 (S ~ \nu^\alpha) is dominated by its steep spectrum shell emission
(\alpha ~ -0.57), although a flat spectrum core structure classifies G11.2-0.3
as a composite supernova remnant. A radial magnetic field structure is
observed. An analysis of the multi-frequency polarization data results in
highly varying rotation measures along the shell. The percentage polarization
is rather low (~2%) and we conclude that G11.2-0.3 is in the transient phase
from free to adiabatic expansion. The central flat spectrum component is partly
resolved. A compact radio source with an inverted spectrum likely coincides
with the previously detected X-ray pulsar (Torii et al. (1997). Two symmetric
structures with flat radio spectra possibly indicate a bipolar outflow.
Combining available X-ray and radio data we conclude that G11.2-0.3 is likely
the remnant of a type II supernova explosion with an early type B progenitor
star.


title:
Temperature profiles of accretion discs around rapidly rotating strange
  stars in general relativity: a comparison with neutron stars

abstract:
  We compute the temperature profiles of accretion discs around rapidly
rotating strange stars, using constant gravitational mass equilibrium sequences
of these objects, considering the full effect of general relativity. Beyond a
certain critical value of stellar angular momentum ($J$), we observe the radius
($r_{\rm orb}$) of the innermost stable circular orbit (ISCO) to increase with
J (a property seen neither in rotating black holes nor in rotating neutron
stars). The reason for this is traced to the crucial dependence of $dr_{\rm
orb}/dJ$ on the rate of change of the radial gradient of the Keplerian angular
velocity at $r_{\rm orb}$ with respect to $J$. The structure parameters and
temperature profiles obtained are compared with those of neutron stars, as an
attempt to provide signatures for distinguishing between the two. We show that
when the full gamut of strange star equation of state models, with varying
degrees of stiffness are considered, there exists a substantial overlap in
properties of both neutron stars and strange stars. However, applying accretion
disc model constraints to rule out stiff strange star equation of state models,
we notice that neutron stars and strange stars exclusively occupy certain
parameter spaces. This result implies the possibility of distinguishing these
objects from each other by sensitive observations through future X-ray
detectors.


title: Luminosities of Disk--accreting Non--magnetic Neutron Stars

abstract:
  Disk accretion onto a neutron star possessing a weak surface magnetic field
($B \le 10^8$ G) provides interesting X-ray emission scenarios, and is relevant
for understanding X-ray bursters and low-mass X-ray binaries (LMXBs). The
standard (Newtonian) theory of disk-accretion predicts that the matter
spiralling in from infinity loses one-half of its total gravitational energy in
the extended disk, and the remainder in a narrow boundary layer girdling the
neutron star. The ratio of the boundary layer luminosity to that from the disk
($E_{\rm BL}/E_{\rm D}$) is, therefore, unity. On incorporation of general
relativity without rotation (Schwarzschild solution), $E_{\rm BL}/E_{\rm D}$ is
seen to be as high as 6. We construct rotating sequences of neutron stars for
three representative equations of state. We show here that for a neutron star
rotating at a limit where centrifugal force balances the inward gravitational
force, $E_{\rm BL}/E_{\rm D}\sim 0$.


title: Warm and Hot Diffuse Gas in Dwarf Galaxies

abstract:
  Dwarf galaxies provide a special environment due to their low mass, small
size and generally low metal content. These attributes make them perfect
laboratories for the interaction of massive stars with the interstellar medium
on small and especially large spatial scales. The natural result of the
spatially concentrated energy output from stellar winds and supernovae of an OB
association is an expanding bubble. These bubbles can grow to kpc-size and
become the dominant driver of the chemical and dynamical evolution of dwarf
galaxies. In such low mass systems, bubbles have an enhanced probability of
breaking out of the gaseous disk into the halo of the host galaxy. This may
lead to venting metal enriched hot gas to large distances from the sites of
creation. In this work I review the current observational material on hot gas
inside bubbles, blow-outs, and hot halos of dwarf galaxies and discuss several
conclusions which can be drawn from the observations. I will also present an
analysis of the dwarf galaxy NGC 1705 as a case study, highlighting
observational methods and problems with the current data. Finally I will
comment on some areas where large progress should be possible in the near
future.


title: Binary and Millisecond Pulsars at the New Millennium

abstract:
  We review the properties and applications of binary and millisecond pulsars.
Our knowledge of these exciting objects has greatly increased in recent years,
mainly due to successful surveys which have brought the known pulsar population
to over 1300. There are now 56 binary and millisecond pulsars in the Galactic
disk and a further 47 in globular clusters. This review is concerned primarily
with the results and spin-offs from these surveys which are of particular
interest to the relativity community.


title: Orbital Comptonization in accretion disks around black holes

abstract:
  We have performed Monte Carlo simulations of Compton upscattering of
low-energy photons in an accretion disk around a Schwarzschild black hole. The
photons gain energy from the rotational motion of the electrons in the disk.
The upscattering occurs near the black hole horizon, where the flow velocity of
the electrons approaches the speed of light. We show that this type of
bulk-flow Comptonization can produce power-law X-ray spectra similar to the
ones observed in black-hole X-ray transients in the high/soft state, i.e., a
soft bump dominating the spectrum below ~ 10 keV and a power-law tail with
photon index in the range 2-3. In order to reproduce the observed hard to soft
flux ratio the disk has to have vertical optical depth above ~ 3 at the last
stable orbit. We conclude that the power-law component of the high/soft state
of black-hole transients may be due to an intrinsically cool disk extending all
the way to the hole, without a separate hot plasma component.


title: Inferring Initial Spin Periods for Neutron Stars in Composite Remnant

abstract:
  We propose a method to infer the initial spin period of pulsars residing in
composite supernova remnants. Such a remnant consists of both a plerionic and a
shell type component, corresponding respectively to the pulsar wind nebula
driven by the spindown luminosity of the central pulsar, and the blastwave
bounding the supernova remnant. Theoretical investigations including
hydrodynamical simulations have shown that at late times (~ 1,000 - 10,000
years), a simple scaling law connects the radius of the supernova shell to the
radius of the plerion. The energy content of the plerion and the total
mechanical energy of the supernova remnant enter into this scaling law. One can
use this scaling law to estimate the initial spin period of pulsars residing in
composite remnants. We discuss potential pitfalls of this method, including the
effect of a small remnant age and of strong radiative losses in the plerion.


title: Detection and measurement of planetary systems with GAIA

abstract:
  We use detailed numerical simulations and the $\upsilon$ Andromedae,
planetary system as a template to evaluate the capability of the ESA
Cornerstone Mission GAIA in detecting and measuring multiple planets around
solar-type stars in the neighborhood of the Solar System. For the outer two
planets of the $\upsilon$ Andromedae, system, GAIA high-precision global
astrometric measurements would provide estimates of the full set of orbital
elements and masses accurate to better than 1--10%, and would be capable of
addressing the coplanarity issue by determining the true geometry of the system
with uncertainties of order of a few degrees. Finally, we discuss the
generalization to a variety of configurations of potential planetary systems in
the solar neighborhood for which GAIA could provide accurate measurements of
unique value for the science of extra-solar planets.


title:
Systematic Uncertainties in the Determination of the Primordial 4He
  Abundance

abstract:
  The primordial helium abundance Y_p is commonly inferred from abundance
determinations in low-metallicity extragalactic HII-regions. Such
determinations may be subject to systematic uncertainties that are investigated
here. Particular attention is paid to two effects: icf-corrections for
``imperfect'' ionization structure leading to significant amounts of
(unobservable) neutral helium or hydrogen and ``tcf''-corrections due to
non-uniform temperature. Model HII-regions with a large number of parameters
are constructed and it is shown that required corrections are almost
exclusively functions of two physical parameters: the number of helium- to
hydrogen- ionizing photons in the illuminating continuum Q(He0)/Q(H0), and the
ratio of width to radius delta r_S/r_S of the Stromgren sphere. For clouds of
sufficient He-ionizing photons Q(He0)/Q(H0) >~ 0.15 and non-negligible width of
the Stromgren sphere a significant overestimate of helium abundances may
result. Such clouds show radiation softness parameters in the range -0.4 <~
log(eta) <~ 0.3 coincident with the range of eta in observed HII-regions.
Existing data of HII-regions indeed seem to display a correlation which is
consistent with a typical ~ 2-4% overestimate of helium abundances due to these
effects. In case such an interpretation prevails, and in the absence of other
compensating effects, a significant downward revision of Y_p may result. It is
argued that caution should be exercised regarding the validity of commonly
quoted error bars on Y_p.


title: HST optical spectral index map of the jet of 3C 273

abstract:
  We present HST images at 622 nm and 300 nm of the jet in 3C273 and determine
the run of the optical spectral index at 0.2" along the jet. The smoothness of
spectral index changes shows that the physical conditions are varying smoothly
across the jet. There is no correlation between the optical flux and spectral
index, as would be expected for relativistic electrons suffering strong cooling
due to synchrotron emission. We find no evidence for localized acceleration or
loss sites. This suggests that the spectral shape is not changing much
throughout the jet. We show that relativistic beaming and/or sub-equipartition
magnetic fields cannot remove the discrepancy between light-travel time along
the jet and the lifetime of electrons emitting optical synchrotron radiation.
We consider this further evidence in favour of a distributed electron
acceleration process.


title: Radiation in a Fractal Cosmology

abstract:
  It is shown that Homogeneous radiation can not be included in the Fractal
Cosmological model obtained earlier by assuming an isotropic fractal
cosmography, General Relativity and the Copernican Principle.


title:
4U 1957+11: a persistent low-mass X-ray binary and black-hole candidate
  in the high state?

abstract:
  We report on several pointed Rossi X-ray Timing Explorer observations of the
enigmatic low-mass X-ray binary (LMXB) 4U 1957+11 at different X-ray
luminosities. The luminosity of the source varied by more than a factor of four
on time scales of months to years. The spectrum of the source tends to get
harder when its luminosity increases. Only very weak (1%-2% rms amplitude;
0.001-10 Hz; 2-60 keV) rapid X-ray variability was observed during the
observations. A comparison of the spectral and temporal behaviour of 4U1957+11
with other X-ray binary systems, in particular LMC X-3, indicates that 4U
1957+11 is likely to be a persistent LMXB harboring a black hole and which is
persistently in the black-hole high state. If confirmed, it would be the only
such system known.


title: 21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593

abstract:
  We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS
1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the
spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate
measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and
derive a mass of 1.3e9 solar masses. We compare this value with limits obtained
towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have
been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible
for DLA systems at even modest redshifts without being detectable from their
21-cm emission.


title: H-Band and Spectroscopic Properties of Abell 1644

abstract:
  We discuss H-band (1.65 micrometer) near-infrared photometry of the central
3x3h^{-2} Mpc^2 of Abell 1644 to a limiting M_H~M^*_H+3 (throughout this paper
H_0=100 h km s^{-1} Mpc^{-1}). There are 861 galaxies in the photometric survey
region. We also measured radial velocities of 155 galaxies; 141 of these are
cluster members within 2.44 h^{-1} Mpc of the cluster center. The cluster
velocity dispersion of sigma~1000 km s^{-1} remains constant out to the
limiting radius. We find no evidence for substructure in the cluster. The
cluster mass within R=2.4 h^{-1} Mpc is 7.6+-1.3x10^{14} h^{-1} M_\odot.
  We compute the cluster luminosity function; the Schechter parameters
\alpha=-1.14\pm0.08 and M^*_H=-24.3\pm0.2 (with h=0.5) agree well with other
H-band luminosity functions. From the virial theorem and the caustic method we
compute one of the first mass-to-light ratios at H; the result is M/L_H=82-127
h M_\odot/L_\odot within 1.5 h^{-1} Mpc. This ratio corresponds to 374-579 h
M_\odot/L_\odot at R. The agreement of our IR measurement with previous $M/L$
determinations indicates that at low redshift dust and young stellar
populations may produce only negligible systematic errors in optical
mass-to-light ratios.


title: HI Observations of Interacting Galaxy Pair NGC 4038/9

abstract:
  We present the results of new radio interferometer HI line observations for
the merging galaxy pair NGC 4038/9 (`The Antennae'), obtained using the
Australia Telescope Compact Array. The results improve substantially on those
of van der Hulst (1979) and show in detail the two merging galactic disks and
the two tidal tails produced by their interaction. The small edge-on spiral
dwarf galaxy ESO 572-G045 is also seen near the tip of the southern tail, but
distinct from it. It shows no signs of tidal interaction. The northern tidal
tail of the Antennae shows no HI connection to the disks and has an extension
towards the west. The southern tidal tail is continuous, with a prominent HI
concentration at its tip, roughly at the location of the tidal dwarf galaxy
observed optically by Mirabel, Dottori & Lutz (1992). Clear velocity structure
is seen along the tidal tails and in the galactic disks. Radio continuum images
at 20-cm and 13-cm are also presented, showing the disks in detail.


title: The new two-image gravitational lens system CLASS B2319+051

abstract:
  We report the discovery of a new two-image gravitational lens system from the
Cosmic Lens All-Sky Survey, CLASS B2319+051. Radio imaging with the Very Large
Array (VLA) and Multi-Element Radio-Linked Interferometer Network (MERLIN)
shows two compact components with a flux density ratio of 5:1, separated by
1.36 arcsec. Observations with the Very Long Baseline Array (VLBA) resolve each
of the radio components into a pair of parity-reversed subcomponents. Hubble
Space Telescope (HST) observations with the Near-Infrared Camera and
Multi-Object Spectrometer (NICMOS) show a bright elliptical galaxy (G1)
coincident with the radio position, and a second irregular galaxy (G2) 3.4
arcsec to the northwest. Previous spectroscopic studies have indicated that
these galaxies are at different redshifts: z(G1) = 0.624, z(G2) = 0.588.
Infrared counterparts to the lensed radio components are not detected in the
NICMOS image, and the source redshift has not yet been determined. Preliminary
mass modeling based on the VLBA subcomponent data indicates that the lensing
potential includes a strong external shear contribution. A VLA monitoring
program is currently being undertaken to measure the differential time delay.


title: Eccentric extrasolar planets from resonant Saturn mass companions

abstract: Withdrawn in current form.


title: The QSO - Ultraluminous Infrared Galaxies Connection

abstract:
  For the past several years, our group has pursued a vigorous ground-based
program aimed at understanding the nature of ultraluminous infrared galaxies.
We recently published the results from a optical/near-infrared spectroscopic
survey of a large statistically complete sample of ultraluminous infrared
galaxies (the "IRAS 1-Jy sample"). We now present the results from our recently
completed optical/near-infrared imaging survey of the 1-Jy sample. These data
provide detailed morphological information on both large scale (e.g., intensity
and color profiles, intensity and size of tidal tails and bridges, etc) and
small scale (e.g., nuclear separation, presence of bars, etc) that helps us
constrain the initial conditions necessary to produce galaxies with such high
level of star formation and/or AGN activity. The nature of the interdependence
between some key spectroscopic and morphological parameters in our objects
(e.g., dominant energy source: super-starburst versus quasar, nuclear
separation, merger phase, star formation rate, and infrared luminosity and
color) is used to clarify the connection between starbursts, ultraluminous
infrared galaxies, and quasars.


title: Collapsar Jets, Bubbles and Fe Lines

abstract:
  In the collapsar scenario, gamma ray bursts are caused by relativistic jets
expelled along the rotation axis of a collapsing stellar core. We discuss how
the structure and time-dependence of such jets depends on the stellar envelope
and central engine properties, assuming a steady jet injection. It takes a few
seconds for the jet to bore its way through the stellar core; most of the
energy output during that period goes into a cocoon of relativistic plasma
surrounding the jet. This material subsequently forms a bubble of magnetized
plasma that takes several hours to expand, subrelativistically, through the
envelope of a high-mass supergiant. Jet break-through and a conventional burst
would be expected not only in He stars but possibly also in blue supergiants.
Shock waves and magnetic dissipation in the escaping bubble can contribute a
non thermal UV/X-ray afterglow, and also excite Fe line emission from thermal
gas, in addition to the standard jet deceleration power-law afterglow.


title:
The Origin of C IV Absorption Systems at Redshifts z<1---Discovery of
  Extended C IV Envelopes Around Galaxies

abstract:
  (Abridged) We report the discovery of extended CIV gaseous envelopes around
galaxies of a wide range of luminosity and morphological type. First, we show
that CIV absorption systems are strongly clustered around galaxies on velocity
scales of v < 250 km/s and impact parameter scales of rho < 100 h^{-1} kpc but
not on larger velocity or impact parameter scales. Next, adopting measurements
of galaxy properties presented in previous papers, we examine how properties of
the CIV absorption systems depend on properties of the galaxies. On the basis
of 14 galaxy and absorber pairs and 36 galaxies that do not produce
corresponding CIV absorption lines to within sensitive upper limits, we find
that: (1) Galaxies of a range of morphological type and luminosity appear to
possess extended CIV gaseous envelopes of radius R ~ 100 h^{-1} kpc, with
abrupt boundaries between the CIV absorbing and non-absorbing regions. (2) The
extent of CIV-absorbing gas around galaxies scales with galaxy B-band
luminosity as R \propto L_B^{0.5 +/- 0.1} but does not depend strongly on
galaxy surface brightness, redshift, or morphological type. And (3) the
covering factor of CIV clouds within ~ 100 h^{-1} kpc of galaxies is nearly
unity, but there is a large scatter in the mean number of clouds encountered
along the line of sight. The most significant implication of the study is that
galaxies of a wide range of luminosity and morphological type are surrounded by
chemically enriched gas that extends for at least ~ 100 h^{-1} kpc. We consider
various scenarios that may have produced metals at large galactic distance and
conclude that accreting satellites are most likely to be responsible for
chemically enriched gas at large galactic distances to regular looking
galaxies.


title: The Formation Timescales of Giant Spheroids

abstract:
  We review current progress in the study of the stellar populations of
early-type galaxies, both locally and at intermediate redshifts. In particular,
we focus on the ages of these galaxies and their evolution in hopes of
determining the star formation epochs of their stars. Due to serious remaining
systematic uncertainties, we are unable to constrain these epochs precisely. We
discuss our results on the evolution of stellar populations in the context of
other observables, in particular the evolution of the Fundamental Plane of
early-type galaxies.


title: Horizontal-Branch Morphology as an Age Indicator

abstract:
  We present our recent revision of model constructions for the
horizontal-branch (HB) morphology of globular clusters, which suggests the HB
morphology is more sensitive to age compared to our earlier models. We also
present our high precision CCD photometry for the classic second parameter pair
M3 and M13. The relative age dating based on this photometry indicates that M13
is indeed older than M3 by 1.7 Gyr. This is consistent with the age difference
predicted from our new models, which provides a further support that the HB
morphology is a reliable age indicator in most population II stellar systems.


title:
Atomic diffusion in metal-poor stars: II. Predictions for the Spite
  plateau

abstract:
  We have computed a grid of up-to-date stellar evolutionary models including
atomic diffusion, in order to study the evolution with time of the surface Li
abundance in low-mass metal-poor stars. We discuss in detail the dependence of
the surface Li evolution on the initial metallicity and stellar mass, and
compare the abundances obtained from our models with the available Li
measurements in Pop II stars. While it is widely accepted that the existence of
the Spite Li-plateau for these stars is a strong evidence that diffusion is
inhibited, we show that, when taking into account observational errors,
uncertainties in the Li abundance determinations, in the effective temperature
scale, and in particular the size of the observed samples of stars, the Spite
plateau and the Li abundances in subgiant branch stars can be reproduced also
by models including fully efficient diffusion, provided that the most
metal-poor field halo objects are between 13.5 and 14 Gyr old. We provide the
value of the minimum number of plateau stars to observe, for discriminating
between efficient or inhibited diffusion. From our models with diffusion we
derive that the average Li abundance along the Spite plateau is about a factor
of 2 lower than the primordial one. As a consequence, the derived primordial Li
abundance is consistent with a high helium and low deuterium Big Bang
Nucleosynthesis; this implies a high cosmological baryon density as inferred
from the analyses of the cosmic microwave background.


title:
VLA Observations of the H92alpha line from NGC 5253 and Henize 2-10 :
  Ionized Gas around Super Star Clusters

abstract:
  We have detected the H92alpha radio recombination line from two dwarf
starburst galaxies, NGC 5253 and He 2-10, using the Very Large Array. Both the
line data as well as the radio continuum data are used to model the properties
of the ionized gas in the centers of these galaxies. We consider a
multi-density model for radio recombination lines and show why previous models,
which were based on the assumption of gas at a single density, are valid in
many situations. The models show that the ionized gas has a density of ~10^4
/cc in both galaxies, with an effective size of 2-10 pc and a total mass of
about 10^4 Msun. The derived production rate of Lyman continuum photons is ~2.5
x 10^{52} /s in both the galaxies and the corresponding mass of stars (assuming
a Salpeter IMF) is ~10^5 msun. The implied stellar density shows that the
observed radio recombination lines arise from ionized gas around super star
clusters (SSCs) in both galaxies (these SSCs have been recently detected
through their radio continuum emission). The existence of ~10^4 Msun of ionized
gas within a few parsecs of an SSC places strict constraints on dynamical
models. Using simple arguments, the parameter space for a few possible models
are derived. The well known radio-FIR correlation also holds for NGC 5253,
although the radio emission from this galaxy is almost completely thermal. It
is shown that NGC 5253 is strong evidence that the component of FIR emission
from warm dust is correlated separately with the component of radio emission
from thermal bremsstrahlung.


title: Equilibrium and stability of supermassive stars in binary systems

abstract:
  We investigate the equilibrium and stability of supermassive stars of mass $M
\agt 10^5M_{\odot}$ in binary systems. We find that corotating binaries are
secularly unstable for close, circular orbits with $r \alt
4R(M/10^6M_{\odot})^{1/6}$ where $r$ is the orbital separation and $R$ the
stellar radius. We also show that corotation cannot be achieved for distant
orbits with $r \agt 12 R (M/10^6M_{\odot})^{-11/24}$, since the timescale for
viscous angular momentum transfer associated with tidal torques is longer than
the evolution timescale due to emission of thermal radiation. These facts
suggest that the allowed mass range and orbital separation for corotating
supermassive binary stars is severely restricted. In particular, for
supermassive binary stars of large mass $M \agt 6\times 10^6M_{\odot}$,
corotation cannot be achieved, as viscosity is not adequate to mediate the
transfer between orbital and spin angular momentum. One possible outcome for
binary supermassive stars is the onset of quasi-radial, relativistic
instability which drives each star to collapse prior to merger: We discuss
alternative outcomes of collapse and possible spin states of the resulting
black holes. We estimate the frequency and amplitude of gravitational waves
emitted during several inspiral and collapse scenarios.


title: Binary neutron star mergers in fully general relativistic simulations

abstract:
  We perform 3D numerical simulations for merger of equal mass binary neutron
stars in full general relativity preparing irrotational binary neutron stars in
a quasiequilibrium state as initial conditions. Simulations have been carried
out for a wide range of stiffness of equations of state and compactness of
neutron stars, paying particular attention to the final products and
gravitational waves. We take a fixed uniform grid in Cartesian coordinates with
typical grid size $(293,293,147)$ in $(x,y,z)$ assuming a plane symmetry with
respect to the equatorial plane. A result of one new large-scale simulation
performed with grid size $(505,505,253)$ is also presented.
  We find that the final product depends sensitively on the initial compactness
of the neutron stars: In a merger between sufficiently compact neutron stars, a
black hole is formed in a dynamical timescale. As the compactness is decreased,
the formation timescale becomes longer and longer. For less compact cases, a
differentially rotating massive neutron star is formed instead of a black hole.
In the case of black hole formation, the disk mass around the black hole
appears to be smaller than 1% of the total rest mass. It is also indicated that
waveforms of high-frequency gravitational waves after merger depend strongly on
the compactness of neutron stars.


title: Density waves in the shearing sheet III. Disc heating

abstract:
  The problem of dynamical heating of galactic discs by spiral density waves is
discussed using the shearing sheet model. The secular evolution of the disc is
described quantitatively by a diffusion equation for the distribution function
of stars in the space spanned by integrals of motion of the stars, in
particular the radial action integral and an integral related to the angular
momentum. Specifically, disc heating by a succession of transient, `swing
amplified' density waves is studied. It is shown that such density waves lead
predominantly to diffusion of stars in radial action space. The stochastical
changes of angular momenta of the stars and the corresponding stochastic
changes of the guiding centre radii of the stellar orbits induced by this
process are much smaller.


title:
Statistical evaluation of the observational information on $\Omega_m$
  and $\Omega_\Lambda$

abstract:
  We undertake a critical evaluation of recent observational information on
$\Omega_m$ and $\Omega_\Lambda$ in order to identify possible sources of
systematic errors and effects of simplified statistical analyses. We combine
observations for which the results have been published in the form of
likelihood contours in the $\Omega_m ,\Omega_\Lambda$ plane. We approximate the
contours by fifth order polynomials, and we then use the maximum likelihood
method to obtain joint likelihood contours for the combined data. In the choice
of statistical merits we aim at minimum loss of information rather than at
minimum variance. We find that $\Omega_0 = \Omega_m + \Omega_\Lambda = 0.99\pm
0.04 \pm 0.03$, where the first error is mainly statistical and the second
error is systematical. In a flat Universe we find $\Omega_m^{flat} = 0.31 \pm
0.04 \pm 0.04$.


title: Screening the Hipparcos-based astrometric orbits of sub-stellar objects

abstract:
  The combination of Hipparcos astrometric data with the spectroscopic data of
putative extrasolar planets seems to indicate that a significant fraction of
these low-mass companions could be brown or M dwarfs Han et al. (2001). We show
that this is due to the adopted reduction procedure, and consequently that the
Hipparcos data do not reject the planetary mass hypothesis in all but one
cases. Additional companions, undetected so far, might also explain the large
astrometric residuals of some of these stars.


title: Modelling X-ray variability in the structured atmospheres of hot stars

abstract:
  We describe X-ray production in the atmospheres of hot, early-type stars in
the framework of a ``stochastic shock model''. The extended envelope of a star
is assumed to possess numerous X-ray emitting ``hot'' zones that are produced
by shocks and embedded in the ambient ``cold'' medium in dynamical equilibrium.
It is shown that the apparent lack of X-ray variability on short (order of
hours) timescales do not contradict a shock model for X-ray production. The
character of the X-ray variability is found to depend on the frequency with
which hot zones are generated, the cool wind opacity to X-rays, and the wind
flow parameters, such as mass loss rate and terminal speed.


title: Beware the Non-uniqueness of Einstein Rings

abstract:
  We explain how an approximation to the rings formed by the host galaxies in
lensed QSOs can be inferred from the QSO data alone. A simple ring image can be
made from any lens model by a simple piece of computer graphics: just plot a
contour map of the arrival-time surface with closely-spaced contours. We go on
to explain that rings should be (a) sensitive to time-delay ratios between
different pairs of images, but (b) very insensitive to H_0. We illustrate this
for the well-known quads 1115+080 and 1608+656.


title: Gas phase production of NHD2 in L134N

abstract:
  We show analytically that large abundances of NH2D and NHD2 can be produced
by gas phase chemistry in the interiors of cold dense clouds. The calculated
fractionation ratios are in good agreement with the values that have been
previously determined in L134N and suggest that triply-deuterated ammonia could
be detectable in dark clouds. Grain surface reactions may lead to similar NH2D
and NHD2 enhancements but, we argue, are unlikely to contribute to the
deuteration observed in L134N.


title: Biomolecules in the Interstellar Medium and Comets

abstract:
  We review recent studies of organic molecule formation in dense molecular
clouds and in comets. We summarise the known organic inventories of molecular
clouds and recent comets, particularly Hale-Bopp. The principal chemical
formation pathways involving gas phase reactions, as well as formation by
catalytic reactions on grain surfaces or through dust fragmentation, are
identified for both dense clouds and cometary comae. The processes leading to
organic molecules with known biological function, carbon chains, deuterium
fractionation, HNC and S-bearing compounds are described. Observational
searches for new interstellar organics are outlined and the connection between
observed interstellar organics and those detected in comets Hale-Bopp and
Hyakutake are discussed.


title:
The pair-wise velocity dispersion of galaxies: effects of non radial
  motions

abstract:
  I discuss the effect of non-radial motions on the small-scale pairwise
peculiar velocity dispersions of galaxies (PVD) in a CDM model. I calculate the
PVD for the SCDM model by means of the refined cosmic virial theorem (CVT)
(Suto & Jing 1997) and taking account of non-radial motions by means of Del
Popolo & Gambera (1998) model. I compare the results of the present model with
the data from Davis & Peebles (1983), the IRAS value at 1 h{-1} Mpc of Fisher
et al. (1993) and Marzke et al. (1995). I show that while the SCDM model
disagrees with the observed values, as pointed out by several authors (Peebles
1976, 1980; Davis & Peebles 1983; Mo et. al 1993; Jing et al. 1998), taking
account of non-radial motions produce smaller values for the PVD. At r <=1
h^{-1} Mpc the result is in agreement with Bartlett & Blanchard (1996)
(hereafter BB96). At the light of this last paper, the result may be also read
as a strong dependence of the CVT prediction on the model chosen to describe
the mass distribution around galaxies, suggesting that the CVT cannot be taken
as a direct evidence of a low density universe. Similarly to what shown in Del
Popolo & Gambera (1999, 2000) (hereafter DG99, DG00), Del Popolo et al. (1999),
the agreement of our model to the observational data is due to a scale
dependent bias induced by the presence of non-radial motions. Since the
assumptions on which CVT is based have been questioned by several authors
(BB96; SJ97), I also calculated the PVD using the redshift distortion in the
redshift-space correlation function, \xi_z(r_p,\pi), and I compared it with the
PVD measured from the Las Campanas Redshift Survey by J98. The result confirms
that non-radial motions influence the PVD making them better agree with
observed data.


title: Mining the Sky with Redshift Surveys

abstract:
  Since the late 1970's, redshift surveys have been vital for progress in
understanding large-scale structure in the Universe. The original CfA redshift
survey collected spectra of 20-30 galaxies per clear night on a 1.5 meter
telescope; over a two year period the project added ~2000 new redshifts to the
literature. Subsequent low-z redshift surveys have been up to an order of
magnitude larger, and ongoing surveys will yield a similar improvement over the
generation preceding them. Full sky redshift surveys have a special role to
play as predictors of cosmological flows, and deep pencil beam surveys have
provided fundamental constraints on the evolution of properties of galaxies.
With the 2DF redshift survey and the SDSS survey, our knowledge of the
statistical clustering of low-redshift galaxies will achieve unprecedented
precision. Measurements of clustering in the distant Universe are more limited
at present, but will become much better in this decade as the VLT/VIRMOS and
Keck/DEIMOS projects produce results. As in so many other fields, progress in
large scale structure studies, both observational and theoretical, has been
made possible by improvements in technologies, especially computing. This
review briefly highlights twenty years of progress in this evolving discipline
and describes a few novel cosmological tests that will be attempted with the
Keck/DEIMOS survey.


title: The CMB power spectrum at l=30-200 from QMASK

abstract:
  We measure the cosmic microwave background (CMB) power spectrum on angular
scales l~30-200 (1-6 degrees) from the QMASK map, which combines the data from
the QMAP and Saskatoon experiments. Since the accuracy of recent measurements
leftward of the first acoustic peak is limited by sample-variance, the large
area of the QMASK map (648 square degrees) allows us to place among the
sharpest constraints to date in this range, in good agreement with BOOMERanG
and (on the largest scales) COBE/DMR. By band-pass-filtering the QMAP and
Saskatoon maps, we are able to spatially compare them scale-by-scale to check
for beam- and pointing-related systematic errors.


title: Interstellar Bubbles in Two Young HII Regions

abstract:
  Massive stars are expected to produce wind-blown bubbles in the interstellar
medium; however, ring nebulae, suggesting the existence of bubbles, are rarely
seen around main-sequence O stars. To search for wind-blown bubbles around
main-sequence O stars, we have obtained high-resolution Hubble Space Telescope
WFPC2 images and high-dispersion echelle spectra of two pristine HII regions,
N11B and N180B, in the Large Magellanic Cloud. These HII regions are ionized by
OB associations that still contain O3 stars, suggesting that the HII regions
are young and have not hosted any supernova explosions. Our observations show
that wind-blown bubbles in these HII regions can be detected kinematically but
not morphologically because their expansion velocities are comparable to or
only slightly higher than the isothermal sound velocity in the HII regions.
Bubbles are detected around concentrations of massive stars, individual O
stars, and even an evolved red supergiant (a fossil bubble). Comparisons
between the observed bubble dynamics and model predictions show a large
discrepancy (1--2 orders of magnitude) between the stellar wind luminosity
derived from bubble observations and models and that derived from observations
of stellar winds. The number and distribution of bubbles in N11B differ from
those in N180B, which can be explained by the difference in the richness of
stellar content between these two HII regions. Most of the bubbles observed in
N11B and N180B show a blister-structure, indicating that the stars were formed
on the surfaces of dense clouds. Numerous small dust clouds, similar to Bok
globules or elephant trunks, are detected in these HII regions and at least one
of them hosts on-going star formation.


title:
A detailed study of the 5 Hz quasi-periodic oscillations in the bright
  X-ray transient and black-hole candidate GRS 1739-278

abstract:
  We present a detailed study of the 5 Hz quasi-periodic oscillation (QPO)
recently discovered in the bright X-ray transient and black-hole candidate GRS
1739-278 (Borozdin & Trudolyubov 2000) during a Rossi X-ray Timing Explorer
observation taken on 1996 March 31. In total 6.6 ksec of on-source data were
obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by
2.6 ksec. The 5 Hz QPO was only present during the second data set. The QPO
increased in strength from below 2% rms amplitude for photon energies below 4
keV to ~5% rms amplitude for energies above 10 keV. The soft QPO photons (below
5 keV) lagged the hard ones (above 10 keV) by almost 1.5 radian. Besides the
QPO fundamental, its first overtone was detected. The strength of the overtone
increased with photon energy (from <2% rms below 5 keV to ~8% rms above 10
keV). Although the limited statistics did not allow for an accurate
determination of the lags of the first overtone, indications are that also for
this QPO the soft photons lagged the hard ones. When the 5 Hz QPO was not
detected (i.e., during the first part of the observation), a broad noise
component was found for photon energies below 10 keV but it became almost a
true QPO (with a Q value of ~1.9) above that energy, with a frequency of ~3 Hz.
Its hard photons preceded the soft ones in a way reminiscent of the 5 Hz QPO,
strongly suggesting that both features are physically related. We discuss our
finding in the frame work of low-frequency QPOs and their properties in BHCs.