title:
Extragalactic Gamma-ray Absorption and the Intrinsic Spectrum of Mkn 501
  During the 1997 Flare

abstract:
  Using the recent models of Malkan & Stecker (2001) for the infrared
background radiation and extrapolating them into the optical and UV range using
recent galaxy count data, we rederive the optical depth of the Universe to high
energy gamma-rays as a function of energy and redshift for energies between 50
GeV and 100 TeV and redshifts between 0.03 and 0.3. We then use these results
to derive the intrinsic gamma-ray spectrum of Mkn 501 during its 1997 high
state. We find that the time averaged spectral energy distribution of Mkn 501
while flaring had a broad, flat peak in the 5 to 10 TeV range which corresponds
to a broad, flat time averaged X-ray peak in the 50 to 100 keV range observed
during the flare. The spectral index of our derived intrinsic differential
photon spectrum for Mkn 501 at energies below about 2 TeV was found to be apx.
1.6 to 1.7. This corresponds to a time averaged spectral index of 1.76 found in
soft X-rays at energies below the X-ray (synchrotron) peak. These results
appear to favor a synchrotron-self Compton origin for the TeV emission together
wuth jet parameters which are consistent with time variability constraints
within the context of a simple SSC model.


title: Constrained Simulations of the Real Universe: the Local Supercluster

abstract:
  We present cosmological simulations which closely mimic the real Universe
within 100Mpc of the Local Group. The simulations, called Constrained
Simulations, reproduce the large-scale density field with major nearby
structures, including the Local Group, the Coma and Virgo clusters, the Great
Attractor, the Perseus-Pices, and the Local Supercluster, in approximately
correct locations. The MARK III survey of peculiar velocities of the observed
structures inside 80Mpc/h sphere is used to constrain the initial conditions.
Fourier modes on scales larger then 5Mpc/h are dominated by the constraints,
while small scale waves are random. The main aim of this paper is the structure
of the Local Supercluster (LSC; 30Mpc/h around the Virgo cluster) and the Local
Group environment. We find that at the current epoch most of the mass
(7.5e14Msun/h) of the LSC is located in a filament roughly centered on the
Virgo cluster and extending over 40Mpc/h. The simulated Local Group (LG) is
located in an adjacent smaller filament, which is not a part of the main body
of the LSC, and has a peculiar velocity of 250kms toward the Virgo cluster. The
peculiar velocity field in the LSC region is complicated and is drastically
different from the field assumed in the Virgocentric infall models. The
peculiar velocity flow in the vicinity of the LG in the simulation is ``cold'':
the peculiar line-of-sight velocity dispersion within 7Mpc/h of the LG is less
than 60km/s, comparable to the observed velocity dispersion of nearby galaxies.


title: Spectral Indices of Stars at Super-solar Regime

abstract:
  We derived Lick narrow-band indices for 139 candidate super metal-rich stars
of different luminosity class previously studied in Malagnini et al. (2000).
Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By
comparing observations with Kurucz' synthetic model atmospheres, no evidence is
found for non-standard Mg vs. Fe relative abundance (i.e. [Mg/Fe]~ 0, on the
average, for our sample). A comparison with the Worthey et al.(1994) and
Buzzoni et al.(1992, 1994) fitting function predictions for [Fe/H] > 0 is
performed and briefly discussed.


title: GRB Phenomenology, Shock Dynamo, and the First Magnetic Fields

abstract:
  A relativistic collisionless shock propagating into an unmagnetized medium
leaves behind a strong large-scale magnetic field. This seems to follow from
two assumptions: (i) GRB afterglows are explained by synchrotron emission of a
relativistic shock, (ii) magnetic field can't exist on microscopic scales only,
it would decay by phase space mixing. Assumption (i) is generally accepted
because of an apparent success of the shock synchrotron phenomenological model
of GRB afterglow. Assumption (ii) is confirmed in this work by a
low-dimensional numerical simulation. One may hypothesize that relativistic
shock velocities are not essential for the magnetic field generation, and that
all collisionless shocks propagating into an unmagnetized medium generate
strong large-scale magnetic fields. If this hypothesis is true, the first
cosmical magnetic fields could have been generated in shocks of the first
virialized objects.


title:
Caltech Faint Galaxy Redshift Survey XVI: The Luminosity Function for
  Galaxies in the Region of the HDF-North to z = 1.5

abstract:
  We have carried out a study of the luminosity function (henceforth LF) of
galaxies in the region of the HDF-North using our very complete redshift
catalog. We solve for the LF at four rest frame wavelengths from 0.24 to 2.2mu.
We find that the LFs for quiescent galaxies have shallow faint end slopes,
while those of galaxies with detectable emission lines have steeper faint end
slopes. Furthermore these slopes are independent of redshift out to z=1.05 for
each galaxy spectral grouping and agree well with comparable local
determinations. We find that galaxies with strong absorption lines become
brighter with z with Q \sim 0.6 at all rest frame bands studied here, where Q =
\Delta{\rm{log}}[L^*(z)]/\Delta{z}, while galaxies with detectable emission
lines (i.e. star forming galaxies) show a smaller change in L^* with redshift
at all bands, Q ~ 0.3, with Q becoming significantly larger at rest frame
2400A. Passive evolution models of galaxies are in reasonable agreement with
these results for absorption line dominated galaxies, while plausible star
formation histories can reproduce the behavior of the emission line galaxies.
We find the co-moving number density and stellar mass in galaxies to be
approximately constant out to z~1.05, and with more uncertainty, to z~1.3. The
major epoch(s) of star formation and of galaxy formation must have occurred
even earlier. (abridged)


title:
Multiwavelength Observations of the Low Metallicity Blue Compact Dwarf
  Galaxy SBS 0335-052

abstract:
  New infrared and millimeter observations from Keck, Palomar, ISO, and OVRO
and archival data from the NRAO VLA and IRAS are presented for the low
metallicity blue compact dwarf galaxy SBS 0335-052. Mid-infrared imaging shows
this young star-forming system is compact (0.31"; 80 pc) at 12.5 microns. The
large Br-gamma equivalent width (235 Angstroms) measured from integral field
spectroscopy is indicative of a ~5 Myr starburst. The central source appears to
be optically thin in emission, containing both a warm (~80 K) and a hot (~210
K) dust component, and the overall interstellar radiation field is quite
intense, about 10,000 times the intensity in the solar neighborhood. CO
emission is not detected, though the galaxy shows an extremely high global H I
gas-to-dust mass ratio, high even for blue compact dwarfs. Finally, the
galaxy's mid-infrared-to-optical and mid-to-near-infrared luminosity ratios are
quite high, whereas its far-infrared-to-radio and far-infrared-to-optical flux
ratios are surprisingly similar to what is seen in normal star-forming
galaxies. The relatively high bolometric infrared-to-radio ratio is more easily
understood in the context of such a young system with negligible nonthermal
radio continuum emission. These new lines of evidence may outline features
common to primordial galaxies found at high redshift.


title: Supernova OH (1720 MHz) Masers in Sgr A East, W28 and G359.1-0.5

abstract:
  A new class of OH (1720 MHz) masers unaccompanied by main-line transitions
have recently been discovered (Frail, Goss and Slysh 1994). These masers lie at
the interface between supernova remnants (SNRs) interacting with molecular
clouds. We discuss three new aspects of SN masers found in the direction toward
the Galactic center: (i) the detection of a new --130 \kms OH (1720 MHz) maser
in the southern lobe of the molecular ring at the Galactic center, (ii) the
detection of extended OH (1720 MHz) maser emission from W28 accompanying the
compact maser sources and (iii) the detection of linear polarization of the
brightest OH (1720 MHz) maser in SNR G359.1--0.5.


title: The Nature of the Compact Supernova Remnants in Starburst Galaxies

abstract:
  Radio observations of starburst regions in galaxies have revealed groups of
compact nonthermal sources that may be radiative supernova remnants expanding
in the interclump medium of molecular clouds. Because of the high pressure in
starburst regions, the interclump medium may have a density ~ 10^3 H atoms
cm^{-3} in a starburst nucleus like M82 and ~ 10^4 H atoms cm^{-3} in an
ultraluminous galaxy like Arp 220. In M82, our model can account for the sizes,
the slow evolution, the high radio luminosities, and the low X-ray luminosities
of the sources. We predict expansion velocities ~ 500 km/s, which is slower
than the one case measured by VLBI techniques. Although we predict the remnants
to be radiative, the expected radiation is difficult to detect because it is at
infrared wavelengths and the starburst is itself very luminous; one detection
possibility is broad [OI] 63 micron line emission at the positions of the radio
remnants. The more luminous and compact remnants in Arp 220 can be accounted
for by the higher molecular cloud density. In our model, the observed remnants
lose most of the supernova energy to radiation. Other explosions in a lower
density medium may directly heat a hot, low density interstellar component,
leading to the superwinds that are associated with starburst regions.


title: X-rays and Protostars in the Trifid Nebula

abstract:
  The Trifid Nebula is a young HII region recently rediscovered as a
"pre-Orion" star forming region, containing protostars undergoing violent mass
ejections visible in optical jets as seen in images from the Infrared Space
Observatory and the Hubble Space Telescope. We report the first X-ray
observations of the Trifid nebula using ROSAT and ASCA. The ROSAT image shows a
dozen X-ray sources, with the brightest X-ray source being the O7 star, HD
164492, which provides most of the ionization in the nebula. We also identify
85 T Tauri star and young, massive star candidates from near-infrared colors
using the JHKs color-color diagram from the Two Micron All Sky Survey (2MASS).
Ten X-ray sources have counterpart near-infrared sources. The 2MASS stars and
X-ray sources suggest there are potentially numerous protostars in the young
HII region of the Trifid. ASCA moderate resolution spectroscopy of the
brightest source shows hard emission up to 10 keV with a clearly detected Fe K
line. The best model fit is a two-temperature (T = 1.2x10^6 K and 39x10^6 K)
thermal model with additional warm absorbing media. The hotter component has an
unusually high temperature for either an O star or an HII region; a typical
Galactic HII region could not be the primary source for such hot temperature
plasma and the Fe XXV line emission. We suggest that the hotter component
originates in either the interaction of the wind with another object (a
companion star or a dense region of the nebula) or from flares from deeply
embedded young stars.


title:
Observations of flat-spectrum radio sources at 850 microns from the
  James Clerk Maxwell Telescope I. April 1997--April 2000

abstract:
  Calibrated data for 65 flat-spectrum extragalactic radio sources are
presented at a wavelength of 850 microns covering a three-year period from
April 1997. The data, obtained from the James Clerk Maxwell Telescope using the
SCUBA camera in pointing mode, were analysed using an automated pipeline
process based on the Observatory Reduction and Acquisition Control - Data
Reduction (ORAC-DR) system. This paper describes the techniques used to analyse
and calibrate the data and presents the database of results along with a
representative sample of the better-sampled lightcurves.


title:
Cutoff in the TeV Energy Spectrum of Markarian 421 During Strong Flares
  in 2001

abstract:
  Exceptionally strong and long lasting flaring activity of the blazar
Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the
excellent signal-to-noise ratio of the data we derive the energy spectrum
between 260 GeV - 17 TeV with unprecedented statistical precision. The spectrum
is not well described by a simple power law even with a curvature term. Instead
the data can be described by a power law with exponential cutoff: $\rm
{{dN}\over{dE}} \propto \rm E^{-2.14 \pm 0.03_{stat}} \times e^{-E/E_{0}}
m^{-2} s^{-1} TeV^{-1}$ with $\rm E_{0} = 4.3 \pm 0.3_{stat} TeV$. Mrk 421 is
the second $\gamma$-ray blazar that unambiguously exhibits an absorption-like
feature in its spectral energy distribution at 3-6 TeV suggesting that this may
be a universal phenomenon, possibly due to the extragalactic infra-red
background radiation.


title:
Abundances in Stars from the Red Giant Branch Tip to the Near the Main
  Sequence Turn Off in M71: III. O, Na, Si, Ca, Ti, Cr, & Ni

abstract: This paper was heavily modified and resubmitted as astro-ph/0111572.


title:
Another intermediate mass black hole in a starburst galaxy?: The
  luminous X-ray source in NGC 3628 reappears

abstract:
  In a 52 ks-long Chandra ACIS-S observation of the nearby starburst galaxy NGC
3628, obtained to study the starburst-driven outflow from this galaxy, we have
detected a very luminous (L_X = 1.1e40 erg/s in the 0.3-8.0 keV energy band)
point source located at least 20 arcsec (~970 pc) from the nucleus of the
galaxy. No radio, optical or near-IR counterpart to this source has been found.
  This is most probably the reappearance of the strongly-variable
X-ray-luminous source discovered by Dahlem et al (1995), which faded by a
factor >27 between December 1991 and March 1994 (at which point it had faded
below the detection limit in a ROSAT HRI observation). This source is clearly a
member of an enigmatic class of X-ray sources that are considerably more
luminous than conventional X-ray binaries but less luminous than AGN, and which
are not found at the dynamical center of the host galaxy.
  The Chandra spectrum is best-fit by an absorbed power law model with a photon
index of Gamma = 1.8+/-0.2, similar to that seen in Galactic BH binary
candidates in their hard state. Bremsstrahlung models or multi-color disk
models (the favored spectral model for objects in this class based on ASCA
observations) can provide statistically acceptable fits only if the data at
energies E > 5 keV is ignored. This is one of the first X-ray spectra of such
an object that is unambiguously that of the source alone, free from the
spectral contamination by X-ray emission from the rest of the galaxy that
affects previous spectral studies of these objects using ASCA.


title: Starburst-driven galactic superwinds

abstract:
  I provide an observational review of the properties of starburst-driven
galactic superwinds, focusing mainly on recent results pertinent to the
transport of metals and energy into the IGM. Absorption-line studies are
providing rich kinematic information on both neutral and ionized gas in
superwinds, with observed mass flow rates similar to the star formation rate
and outflow velocities comparable to or greater than the escape velocity. FUSE
observations of the Ovi doublet provide previously unattainable information
regarding outflow velocities and radiative cooling rates in hot gas at T \sim
3\times 10^{5} K. Emission from gas at temperatures of 10^{4} K and \sim 5
\times 10^{6} K is now being studied with unprecedented spatial resolution
using HST and Chandra, tracing the complex interaction of the still-invisible
wind of SN-ejecta with the ambient ISM entrained into these outflows. I discuss
the implications of these observations for our understanding of
starburst-driven outflows.


title: A new formation model for M32: A threshed early-type spiral?

abstract:
  The origin of the closest compact elliptical galaxy (cE) M32 is a
longstanding problem of galaxy formation in the Local Group. Our N-body/SPH
simulations suggest a new scenario in which the strong tidal field of M31 can
transform a spiral galaxy into a compact elliptical. As a low luminosity spiral
galaxy plunges into the central region of M31, most of the outer stellar and
gaseous components of its disk are dramatically stripped due to M31's tidal
field The central bulge component, on the other hand, is just weakly influenced
by the tidal field owing to its compact configuration, and retains its
morphology. M31's strong tidal field also induces rapid gas transfer to the
central region, triggers a nuclear starburst, and consequently forms the
central high density and more metal-rich stellar populations with relatively
young ages. Thus, in this scenario, M32 was previously the bulge of a spiral
tidally interacting with M31 several Gyr ago. Furthermore, we suggest cEs like
M32 are rare, the result of both the rather narrow parameter space for tidal
interactions which morphologically transform spirals into cEs and the very
short time scale ($<$ a few $10^9$ yr) for cEs to be swallowed.


title:
Potential formation sites of super star clusters in ultra-luminous
  infrared galaxies

abstract:
  Recent observational results on high spatial resolution images of
ultra-luminous infrared galaxies (ULIGs) have revealed very luminous, young,
compact, and heavily obscured super star clusters in their central regions,
suggested to be formed by gas-rich major mergers. By using stellar and gaseous
numerical simulations of galaxy mergers, we firstly demonstrate that the
central regions of ULIGs are the most promising formation sites of super star
clusters owing to the rather high gaseous pressure of the interstellar medium.
Based on simple analytical arguments, we secondly discuss the possibility that
super star clusters in an ULIG can be efficiently transferred into the nuclear
region owing to dynamical friction and consequently merge with one another to
form a single compact stellar nucleus with a seed massive black hole. We thus
suggest that multiple merging between super star clusters formed by nuclear
starbursts in the central regions of ULIGs can result in the formation of
massive black holes.


title:
Effect of Coriolis force on Accretion Flows around Rotating Compact
  Object

abstract:
  Using the generalised set of fluid equations that include the `Coriolis
force' along with the centrifugal and pressure gradient forces, we have
reanalysed the class of self similar solutions, with the pseudo-Newtonian
potential. We find that the class of solutions is well behaved for almost the
entire parameter space except for a few selected combinations of $\gamma$ and
$\alpha$ for the co-rotating flow. The analysis of the Bernoulli number shows
that whereas it remains positive for co-rotating flow for $f>1/3$, for the
counter-rotating flow it does admit both positive and negative values,
indicating the possibility of energy transfer in either direction.


title:
Study of the photon flux from the night sky at La Palma and Namibia, in
  the wavelength region relevant for imaging atmospheric Cherenkov telescopes

abstract:
  The level of the night sky background light at La Palma and Namibia was
determined, with emphasis on the wavelength region and solid angle coverage
relevant for the operation of imaging atmospheric Cherenkov telescopes. The
dependence of the night sky background light both on celestial coordinates
(alt, az) and on galactic coordinates (b, l) was measured, with an angular
resolution of about 1 degr. Average light levels near the zenith are similar in
both locations -- 2.2 x 10^12 to 2.6 x 10^12 photons per sr s m^2 for 300 nm <
lambda < 650 nm. With increasing zenith angle the level of background light
increases at La Palma, whereas a constant level is measured in Namibia. Near
the center of the Milky Way, background light levels are increased by a factor
up to 4 and more. Also the level of light backscattered from the ground has
been studied.


title: The puzzle of the synthesis of the rare nuclide 138La

abstract:
  The calculations of the p-process in the O/Ne layers of Type II supernovae
are quite successful in reproducung the solar system content of p-nuclides.
They predict, however, a significant underproduction of the rare odd-odd
nuclide 138La. A model for the explosion of a 25 Mo star with solar metallicity
is used to suggest that electron neutrino captures on 138Ba may well be its
most efficient production mechanism. The responsibility of an inadequate
prediction of the 138La and 139La photodisintegration rates in the too low
production of 138La is also examined quantitatively. A detailed discussion of
the theoretical uncertainties in these rates suggest that the required rate
changes are probably too high to be fully plausible. Their measurement would be
most welcome. They would help disentangling the relative contributions of
thermonuclear and neutrino processes to the 138La production.


title:
Gamma-Ray Bursts: Super-Explosions in the Universe and Related
  High-Energy Phenomena

abstract:
  The recent progress in studies of gamma-ray bursts, their afterglows, and
host galaxies is discussed. The emphasis is given to high-energy phenomena
associated with gamma-ray burst explosions: high-energy cosmic rays, neutrinos,
gravitational waves. We also show how the relativistic fireball model for GRBs
can be used to constrain modern theories of large and infinite
extra-dimensions. In particular, in the frame of 5D gravity with the Standard
Model localized on 3D brane (Dvali et al. 2000), the very existence of
relativistic fireballs of $\sim 10^{53}$ ergs puts the lower bound on the
quantum gravity scale $\sim 0.1$ eV.


title: Electromagnetic radiation and motion of arbitrarily shaped particle

abstract:
  Covariant form of equation of motion for arbitrarily shaped particle in the
electromagnetic radiation field is presented. Equation of motion in the proper
frame of the particle uses the radiation pressure cross section 3 $\times$ 3
matrix. The obtained equation of motion is compared with known result.


title:
Analysis of the Hipparcos Observations of the Extrasolar Planets and the
  Brown-Dwarf Candidates

abstract:
  We analyzed the Hipparcos astrometric observations of 47 stars that were
discovered to harbor giant planets and 14 stars with brown-dwarf secondary
candidates. The Hipparcos measurements were used together with the
corresponding stellar radial-velocity data to derive an astrometric orbit for
each system. To find out the significance of the derived astrometric orbits we
applied a "permutation" technique by which we analyzed the permuted Hipparcos
data to get false orbits. The size distribution of these false orbits indicated
the range of possibly random, false orbits that could be derived from the true
data. These tests could not find any astrometric orbit of the planet candidates
with significance higher than 99%, suggesting that most if not all orbits are
not real. Instead, we used the Hipparcos data to set upper limits on the masses
of the planet candidates. The lowest derived upper limit is that of 47UMa -
0.014 solar mass, which confirms the planetary nature of its unseen companion.
For 13 other planet candidates the upper limits exclude the stellar nature of
their companions, although brown-dwarf secondaries are still an option. These
negate the idea that all or most of the extrasolar planets are disguised
stellar secondaries. Of the 14 brown-dwarf candidates, our analysis reproduced
the results of Halbwachs et al., who derived significant astrometric orbits for
6 systems which imply secondaries with stellar masses. We show that another
star, HD164427, which was discovered only very recently, also has a secondary
with stellar mass. Our findings support Halbwachs et al. conclusion about the
possible existence of the "brown-dwarf desert" which separates the planets and
the stellar secondaries.


title: Statistical Properties of DLAs and sub-DLAs

abstract:
  Quasar absorbers provide a powerful observational tool with which to probe
both galaxies and the intergalactic medium up to high redshift. We present a
study of the evolution of the column density distribution, f(N,z), and total
neutral hydrogen mass in high-column density quasar absorbers using data from a
recent high-redshift survey for damped Lyman-alpha (DLA) and Lyman limit system
(LLS) absorbers. Whilst in the redshift range 2 to 3.5, ~90% of the neutral HI
mass is in DLAs, we find that at z>3.5 this fraction drops to only 55% and that
the remaining 'missing' mass fraction of the neutral gas lies in sub-DLAs with
N(HI) 10^{19} - 2 * 10^{20} cm^{-2}.


title:
Dynamics of gravitational clustering II. Steepest-descent method for the
  quasi-linear regime

abstract:
  We develop a non-perturbative method to derive the probability distribution
$P(\delta_R)$ of the density contrast within spherical cells in the
quasi-linear regime. Indeed, since this corresponds to a rare-event limit a
steepest-descent approximation can yield asymptotically exact results. We check
that this is the case for Gaussian initial density fluctuations, where we
recover most of the results obtained by perturbative methods from a
hydrodynamical description. Moreover, we correct an error which was introduced
in previous works for the high-density tail of the pdf. This feature, which
appears for power-spectra with a slope $n<0$, points out the limitations of
perturbative approaches which cannot describe the pdf $P(\delta_R)$ for
$\delta_R \ga 3$ even in the limit $\sigma \to 0$. This break-up does not
involve shell-crossing and it is naturally explained within our framework.
Thus, our approach provides a rigorous treatment of the quasi-linear regime,
which does not rely on the hydrodynamical approximation for the equations of
motion. Besides, it is actually simpler and more intuitive than previous
methods. Our approach can also be applied to non-Gaussian initial conditions.


title:
Interacting Stellar Wind and Photoionization Models of the SN 1987A
  Remnant

abstract:
  We are investigating the SN 1987A remnant by modeling the circumstellar
environment of the progenitor star. Interacting stellar winds models have been
reasonably successful at reproducing the gross features of the nebula, but some
details, such as the early rise of the radio and x-ray emission from the
supernova blast and the presence of the outer rings, are not explained in a
pure wind model. In this paper we describe preliminary results from 2-D models
that incorporate the effects of photoionization due to radiation from the
central star. These models have successfully produced a thick HII region, as
needed to produce the early radio and X-ray emission. The HII region is
thickest away from the equatorial plane. The models have also produced a
feature resembling the outer rings, but we suspect this to be an artifact of
the 2-D calculations that would not persist in 3-D.


title:
In-flight performances of SilEye-2 Experiment and cosmic ray abundances
  inside space station Mir

abstract:
  Cosmic ray measurements performed with the instrument SilEye-2 on Mir space
station are presented. SilEye-2 is a silicon detector telescope for the study
of the causes of Light Flashes perception by astronauts. As a stand-alone
device, it monitors in the short and long term the radiation composition inside
Mir. The cosmic ray detector consists of an array of 6 active silicon strip
detectors which allow nuclear identification of cosmic rays up to Iron. The
device was operational for more than 1000 hours in the years 1998-2000,
measuring also several Solar Particle Events. In this work we present the
in-flight performance of the instrument and nuclear abundance data from Boron
to Silicon above ~150 MeV/n inside Mir.


title: Host galaxies, BH masses and Eddington ratio of radio-loud AGNs

abstract:
  We compare the host galaxies properties of BL Lac objects with those of radio
loud quasars (RLQs) imaged by the WFPC2 on board of HST. The considered objects
(z<0.5) are always well resolved and their host galaxies satisfactorily
modelled by ellipticals. After homogeneous treatment of the data we find RLQs
hosts are systematically more luminous (by ~0.7 mag) with respect to the hosts
of BL Lacs. Using the M_BH - L_bulge relation, derived for nearby elliptical
galaxies, we have evaluated the central black hole masses of our sample of
active galaxies. These data are discussed in conjunction with the nuclear
luminosity and the Eddington ratio.


title: Photons as Ultra High Energy Cosmic Rays ?

abstract:
  We study spectra of the Ultra High Energy Cosmic Rays assuming primaries are
protons and photons, and that their sources are extragalactic. We assume power
low for the injection spectra and take into account the influence of cosmic
microwave, infrared, optical and radio backgrounds as well as extragalactic
magnetic fields on propagation of primaries. Our additional free parameters are
the maximum energy of injected particles and the distance to the nearest
source. We find a parameter range where the Greisen-Zatsepin-Kuzmin cut-off is
avoided.


title:
4U2206+54 - an Unusual High Mass X-ray Binary with a 9.6 Day Orbital
  Period but No Strong Pulsations

abstract:
  Rossi X-ray Timing Explorer All-Sky Monitor observations of the X-ray source
4U2206+54, previously proposed to be a Be star system, show the X-ray flux to
be modulated with a period of approximately 9.6 days. If the modulation is due
to orbital variability then this would be one of the shortest orbital periods
known for a Be star X-ray source. However, the X-ray luminosity is relatively
modest whereas a high luminosity would be predicted if the system contains a
neutron star accreting from the denser inner regions of a Be star envelope.
Although a 392s pulse period was previously reported from EXOSAT observations,
a reexamination of the EXOSAT light curves does not show this or any other
periodicity. An analysis of archival RXTE Proportional Counter Array
observations also fails to show any X-ray pulsations. We consider possible
models that may explain the properties of this source including a neutron star
with accretion halted at the magnetosphere and an accreting white dwarf.


title:
Hubble Space Telescope Observations of the Gravitationally Lensed
  Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging Polarimetry and
  Evidence for Microlensing of a Scattering Region

abstract:
  We report the results of HST WFPC2 broadband F555W and F702W photometric and
F555W polarimetric observations of the "Cloverleaf" QSO H1413+1143. This is a
four-component gravitationally-lensed broad absorption line (BAL) QSO.
Observations were obtained at two epochs in March 1999 and June 1999 separated
by about 100 days. The goal of our program was to detect any relative changes
among the components and between the two epochs. Over this time baseline we
detected an approximately 0.07 mag dimming in component D of the lensed image,
which we interpret as evidence for microlensing. In March 1999 we find
significant evidence for a difference in the relative linear polarization of
component D in comparison to the other three components; in June 1999 the
combined polarization of the Cloverleaf components was lower. In March 1999 the
apparently microlensed component D has a rotated polarization position angle
and a somewhat higher degree of polarization than the other three components.
We suggest that this difference in polarization is due to microlensing
magnification of part of a scattered-light (i.e. polarized) continuum-producing
region. The results indicate that in the Cloverleaf the size-scale of the
polarized scattered-light region exceeds about 10^{16} cm but lies interior to
the region producing the broad emission lines (< 10^{18} cm).


title: Chandra X-ray Sources in M101

abstract:
  A deep (98.2 ks) Chandra Cycle-1 observation has revealed a wealth of
discrete X-ray sources as well as diffuse emission in the nearby face-on spiral
galaxy M101. From this rich dataset we have created a catalog of the 110
sources from the S3 chip detected with a significance of >3 sigma,
corresponding to a flux of ~1.0E-16 ergs/cm/cm/s and a luminosity of 1.0E36
ergs/s for a distance to M101 of 7.2 Mpc. The sources display a distinct
correlation with the spiral arms and include a variety of X-ray binaries,
supersoft sources, supernova remnants, and other objects of which only ~27 are
likely to be background sources. There are only a few sources in the interarm
regions, and most of these have X-ray colors consistent with that of background
AGNs. The derived log N-log S relation for the sources in M101 (background
subtracted) has a slope of -0.80+/-0.05 over the range of 1.0E36 - 1.0E38
ergs/s. The nucleus is resolved into 2 nearly identical X-ray sources, each
with a 0.5-2.0 keV flux of 4.0E37 ergs/s. One of these sources coincides with
the optical nucleus, and the other coincides with a cluster of stars 110 pc to
the south.


title: Relationship of Black Holes to Bulges

abstract:
  Supermassive black holes appear to be uniquely associated with galactic
bulges. The mean ratio of black hole mass to bulge mass was until recently very
uncertain, with ground based, stellar kinematical data giving a value roughly
an order of magnitude larger than other techniques. The discrepancy was
resolved with the discovery of the M-sigma relation, which simultaneously
established a tight corrrelation between black hole mass and bulge velocity
dispersion, and confirmed that the stellar kinematical mass estimates were
systematically too large due to failure to resolve the black hole's sphere of
influence. There is now excellent agreement between the various techniques for
estimating the mean black hole mass, including dynamical mass estimation in
quiescent galaxies; reverberation mapping in active galaxies and quasars; and
computation of the mean density of compact objects based on integrated quasar
light. Implications of the M-sigma relation for the formation of black holes
are discussed.


title: M33: A Galaxy with No Supermassive Black Hole

abstract:
  Galaxies that contain bulges appear to contain central black holes whose
masses correlate with the velocity dispersion of the bulge. We show that no
corresponding relationship applies in the pure disk galaxy M33. Three-integral
dynamical models fit Hubble Space Telescope WFPC2 photometry and STIS
spectroscopy best if the central black hole mass is zero. The upper limit is
1500 M_sun. This is significantly below the mass expected from the velocity
dispersion of the nucleus and far below any mass predicted from the disk
kinematics. Our results suggest that supermassive black holes are associated
only with galaxy bulges and not with their disks.


title: Morphological Measures of nonGaussianity in CMB Maps

abstract:
  We discuss the tests of nonGaussianity in CMB maps using morphological
statistics known as Minkowski functionals. As an example we test degree-scale
cosmic microwave background (CMB) anisotropy for Gaussianity by studying the
\qmask map that was obtained from combining the QMAP and Saskatoon data. We
compute seven morphological functions $M_i(\dt)$, $i=1,...,7$: six \mf and the
number of regions $N_c$ at a hundred $\dt$ levels. We also introduce a new
parameterization of the morphological functions $M_i(A)$ in terms of the total
area $A$ of the excursion set. We show that the latter considerably
decorrelates the morphological statistics and makes them more robust because
they are less sensitive to the measurements at extreme levels. We compare these
results with those from 1000 Gaussian Monte Carlo maps with the same sky
coverage, noise properties and power spectrum, and conclude that the \qmask map
is neither a very typical nor a very exceptional realization of a Gaussian
field. At least about 20% of the 1000 Gaussian Monte Carlo maps differ more
than the \qmask map from the mean morphological parameters of the Gaussian
fields.


title:
The Gaseous Extent of Galaxies and the Origin of Lya Absorption Systems.
  V. Optical and Near-Infrared Photometry of Lya-absorbing Galaxies at z < 1

abstract:
  (Abridged) We present results of a program to obtain and analyze HST WFPC2
images and ground-based images of galaxies identified in an imaging and
spectroscopic survey of faint galaxies in fields of HST spectroscopic target
QSOs. We confirm and improve the results presented by Lanzetta et al. (1995)
and Chen et al. (1998) that (1) extended gaseous envelopes are a common and
generic feature of galaxies of a wide range of luminosity and morphological
type, (2) the extent of tenuous gas (N(H I) > 10^{14} cm^{-2} around galaxies
scales with galaxy B-band luminosity as r\propto L_B^{0.39+/-0.09}, and (3)
galaxy interactions do not play an important role in distributing tenuous gas
around galaxies in most cases. We further demonstrate that (4) the gaseous
extent of galaxies scales with galaxy K-band luminosity as r\propto
L_K^{0.28+/-0.08}, and (5) tenuous gas around typical L_* galaxies is likely to
be distributed in spherical halos of radius ~ 180 h^{-1} kpc of covering factor
of nearly unity. Because galaxies of all morphological types possess extended
gaseous halos and because the extent of tenuous gas around galaxies scales with
galaxy K-band luminosity, we argue that galaxy mass---rather than recent
star-formation activity---is likely to be the dominant factor that determines
the extent of tenuous gas around galaxies. Nevertheless, applying the scaling
relationship between the extent of Lya absorbing gas around galaxies and galaxy
B-band luminosity, the results of our analysis also suggest that the number
density evolution of Lya absorption systems may serve to constrain the
evolution of the comoving galaxy B-band luminosity density (at least for the
redshift interval between z~0 and z~1 that has been studied in our survey).


title: Source Regions of Coronal Mass Ejections

abstract:
  Observations of the solar corona with the Large Angle Spectrometric
Coronograph (LASCO) and Extreme ultraviolet Imaging Telescope (EIT) instruments
on the Solar and Heliospheric Observatory (SOHO) provide an unprecedented
opportunity to study coronal mass ejections (CMEs) from their initiation
through their evolution out to 30 \rsun. The objective of this study is to gain
an understanding of the source regions from which the CMEs emanate. To this
end, we have developed a list of 32 CMEs whose source regions are located on
the solar disk and are well observed in EIT 195 {\AA} data during the period
from so lar minimum in January 1996 through the rising part of the cycle in May
1998. We compare the EIT source regions with photospheric magnetograms from the
Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak
Observatory and also with H$\alpha$ data from various sources. The overall
results of our study show that 41% of the CME related transients observed are
associated with active regions and have no prominence eruptions, 44% are
associated with eruptions of prominences embedded in active regions and 15% are
associated with eruptions of prominences outside active regions. Those CMEs
that do not involve prominence eruptions originate in active regions both with
and without prominences. We describe 6 especially well observed events. These
case studies suggest that active region CMEs (without eruptive prominences) are
associated with active regions with lifetimes between 11--80 days. They are
also often associated with small scale emerging or cancelling flux over
timescales of 6--7 hours. CMEs associated with active region prominence
eruptions, on the other hand, are typically associated with old active regions
with lifetimes $\sim$ 6-7 months.


title:
A model of spectral galaxy evolution including the effects of nebular
  emission

abstract:
  This paper presents a new spectral evolutionary model of galaxies, properly
taking the effects of nebular emission and pre-main sequence evolution into
account. The impact of these features in different photometric filters is
evaluated, along with the influence that variations in the physical conditions
of the gas may have on broadband colours, line ratios and equivalent widths.
Inclusion of nebular emission is demonstrated to radically change the predicted
ultraviolet, optical and near-infrared colours during active star formation.
Pre-main sequence evolution is also seen to give a non-negligible contribution
to the luminosity in the near-infrared during the first few millions years of
evolution and should not be omitted when very young systems are being modelled.
Finally, we present a comparison of our predictions to observations and two
other recent codes of evolutionary synthesis.


title:
Preparation of the COROT space mission: fundamental stellar parameters
  determinations from photometric and spectroscopic analyses for COROT
  potential target candidates

abstract:
  We present a sample of 9 nearby F-type stars with detailed spectroscopic
analyses to investigate the Basel Stellar Library (BaSeL) in two photometric
systems simultaneously, UBV Johnson and uvby Stromgren. The sample corresponds
to potential targets of the central seismology programme of the COROT space
experiment, which have been recently observed at Observatoire de Haute-Provence
(OHP, France). The atmospheric parameters Teff, [Fe/H], and log g obtained from
the BaSeL models are compared with spectroscopic determinations as well as with
results of other photometric calibrations. Moreover, new rotational velocity
determinations are also derived from the spectroscopic analysis and compared
with previous results compiled in the SIMBAD database. All the methods
presented give consistent solutions, and the agreement between Templogg and
BaSeL for the hottest stars of the sample could be especially useful in view of
the well known difficulty of spectroscopic determinations for fast rotating
stars. Finally, we present current and future developments of the BaSeL models
for a systematic application to all the COROT targets. (Abridged)


title: Double Bars, Inner Disks, and Nuclear Rings in Barred Galaxies

abstract:
  We present results of a high-resolution imaging survey of barred S0--Sa
galaxies which demonstrate that the central regions of these galaxies are
surprisingly complex. We see many inner bars --- small, secondary bars
(typically less than a kiloparsec in radius) located inside of, and probably
rotating faster than, the large primary bars. These are present in about one
quarter to one third of all our sample. In contrast to some theoretical
expectations, they do not seem to enhance AGN activity significantly. A third
of barred S0's appear to host kiloparsec-scale disks within their bars; but the
frequency of such inner disks is much lower in our S0/a and Sa galaxies. In
addition, we find one example of a triple barred galaxy, and two cases of
purely stellar nuclear rings --- probably the fossil remnants of past
circumnuclear starbursts.
  We comment briefly on results from an ongoing analysis of known double-barred
systems, extending to Hubble types as late as Sbc, and discuss their
characteristic sizes and orientations.


title: Future supernova probes of quintessence

abstract:
  We investigate the potential of a future supernovae data set, as might be
obtained by the proposed SNAP satellite, to discriminate between two possible
explanations for the observed dimming of the high redshift type IA supernovae,
namely either (i) a cosmological evolution for which the expansion of the
universe has been accelerating for a substantial range of redshifts
$z\goesas1$; or (ii) an unexpected supernova luminosity evolution over such a
redshift range. By evaluating Bayes factors we show that within the context of
spatially flat model universes with a dark energy the future SNAP data set
should be able to discriminate these two possibilities. Our calculations assume
particular cosmological models with a quintessence field in the form of a
dynamical pseudo Nambu--Goldstone boson (PNGB), and a simple empirical model of
the evolution of peak luminosities of the supernovae sources which has been
recently discussed in the literature. We also show that the fiducial SNAP data
set, simulated with the assumption of no source evolution, is able to
discriminate the PNGB model from a number of other spatially flat quintessence
models which have been widely studied in the literature, namely those with
inverse power--law, simple exponential and double--exponential potentials.


title:
Five Years of Magellanic Clouds Research: A Newsletter Editors'
  Perspective

abstract:
  We analyze the topical and demographic evolution of Magellanic Clouds
research over the past five years based on submissions of abstracts of refereed
papers to the electronic Magellanic Clouds Newsletter
(http://www.astro.uiuc.edu/projects/mcnews/MCNews.html).


title: A variable star survey of the open cluster M37

abstract:
  A CCD photometric study of the dense galactic open cluster M37 is presented
and discussed. The majority of the analysed data are time-series measurements
obtained through an R_C filter. The observations were carried out on seven
nights between December 1999 and February 2000, and have led to the discovery
of 7 new variable stars in the field. Three of them have been unambiguously
identified as W UMa-type eclipsing binaries, while two more are monoperiodic
pulsating stars, most probably high-amplitude delta Scuti-type variables. The
remaining two stars seem to be long-period eclipsing binaries without firm
period determination. Johnson B and V frames have been used to construct a new
colour-magnitude (CM) diagram of the cluster, and to find the locations of the
new variable stars. The pulsating variables are most likely background objects.
The CM diagram is fitted with recent isochrones yielding the main parameters of
the cluster.


title: A Search for Supernova-Remnant Masers Toward Unidentified EGRET Sources

abstract:
  Supernova remnants expanding into adjacent molecular clouds are believed to
be sites of cosmic ray acceleration and sources of energetic gamma-rays. Under
certain environmental conditions, such interactions also give rise to unusual
OH masers in which the 1720 MHz satellite line dominates over the more common
1665/7 MHz emission. Motivated by the apparent coincidence of a handful of
EGRET sources with OH(1720 MHz) maser-producing supernova remnants, we have
carried out a search using the Very Large Array for new OH(1720 MHz) masers
within the error regions of 11 unidentified EGRET sources at low Galactic
latitude. While a previously known maser associated with an HII region was
serendipitously detected, initial results indicate that no new masers were
found down to a limiting flux of, typically, 50 mJy. We discuss the
implications of this result on the nature of the unidentified Galactic EGRET
sources.


title: Some Constraints on The Formation of Globular Clusters

abstract:
  We explore the constraints on globular cluster formation provided by the
observed conditions in starbursts where globulars are currently forming, and by
the observed properties of young and old globular clusters. We note that the
pressure in the ISM of starbursts and mergers implies that molecular clouds in
these environments have radii similar to those of globular clusters. Such
molecular clouds are therefore viable precursors to globular clusters if the
star formation efficiency in the clouds is high. A high star formation
efficiency may be a consequence of the high density and associated high binding
energy and short dynamical timescale of molecular clouds in such environments.
We also note that the apparent lack of a mass-radius relationship in young and
old globular cluster systems places important constraints on globular cluster
formation models. This is because molecular clouds are observed to follow a
virial scaling relation between mass and radius. We suggest that a variable
star formation efficiency may weaken or eliminate the mass-radius relation of
molecular clouds as they fragment to form globular clusters. We attribute the
absence of young globular clusters in the disks of ordinary galaxies such as
the Milky Way to the relatively low ambient pressures in such systems.


title: The local Poisson hypothesis for solar flares

abstract:
  The question of whether flares occur as a Poisson process has important
consequences for flare physics. Recently Lepreti et al. presented evidence for
local departure from Poisson statistics in the Geostationary Operational
Environmental Satellite (GOES) X-ray flare catalog. Here it is argued that this
effect arises from a selection effect inherent in the soft X-ray observations;
namely that the slow decay of enhanced flux following a large flare makes
detection of subsequent flares less likely. It is also shown that the power-law
tail of the GOES waiting-time distribution varies with the solar cycle. This
counts against any intrinsic significance to the appearance of a power law, or
to the value of its index.


title:
The European Large Area ISO Survey VI - Discovery of a new hyperluminous
  infrared galaxy

abstract:
  We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in
the course of the European Large Area ISO Survey (ELAIS). This object has been
detected by ISO at 6.7, 15, and 90 microns, and is found to be a broad-line,
radio-quiet quasar at a redshift: z = 1.099. From a detailed multi-component
model fit of the spectral energy distribution, we derive a total infrared
luminosity: L_IR (1-1000 microns) ~ 1.0 x 10E13 h_65^-2 L_sun (q_0 = 0.5), and
discuss the possible existence of a starburst contributing to the far-IR
output. Observations to date present no evidence for lens magnification. This
galaxy is one of the very few HyLIGs with an X-ray detection. On the basis of
its soft X-ray properties, we suggest that this broad-line object may be the
face-on analogue of narrow-line, Seyfert-like HyLIGs.


title:
Measurement of the Cherenkov light spectrum and of the polarization with
  the HEGRA-IACT-system

abstract:
  The HEGRA system of Imaging Atmospheric Cherenkov Telescopes (IACTs) detects
Cherenkov light produced by air showers. The concept of stereoscopic
observation with the five HEGRA telescopes allows the reconstruction of various
shower parameters, for example the shower direction, the location of the shower
core and the energy of cosmic rays. One of the telescopes was modified so that
measurements of the spectrum and the polarization of Cherenkov light with the
HEGRA system were possible. The experimental setup is described and preliminary
results presented.


title: The Heating of the Intra Cluster Medium

abstract:
  X-ray observations indicate that non-gravitational processes play a key role
in determining the distribution of the diffuse, X-ray emitting gas in clusters
of galaxies (ICM). The effect of non-gravitational processes is imprinted in
the ICM as an entropy minimum. Preheating models assume that the entropy
minimum is present in the cosmic baryons well before collapse. On the other
hand, observations of baryons in Ly_alpha clouds show only a modest extra
heating, ruling out the presence of such an entropy plateau in the majority of
low-density baryons at high z. The problem is avoided in the internal heating
scenario, where the heating occurs only inside virialized structures. However,
for internal heating the energy needed to build the entropy minimum is in
excess of 1 keV per particle. It is not clear which kind of source can heat the
baryons: SNae seem to be inefficient by a factor of 3 or more. This energy
crisis must be solved by other sources (like AGNs), unless we are missing some
key aspect of the heating mechanism. The main questions for the next years will
be: when and where is the excess entropy produced, and by which mechanism?


title: BeppoSAX observations of Mrk 841 and Mrk335

abstract:
  We present and discuss BeppoSAX observations of Mrk841 and Mrk335, two
Seyfert 1 galaxies in which previous observations have established the presence
of soft excesses. We confirm the soft excess in both sources, even if for
Mrk~841 a warm absorber provides a fit almost as good as the one with a true
excess. As far as the hard X-ray continuum is concerned, a Comptonization model
provides a fit as good as a power law and a physically sound solution for
Mrk841. For Mrk335, the Comptonization model gives a result which is somewhat
better on statistical ground, but rather problematic on physical ground. The
most interesting results regard the reprocessing components. For Mrk841 we find
a very large reflection continuum but an almost normal iron line equivalent
width even if, within the errors, a solution in which both components are a
factor ~2 larger than expected for an accretion disc is still marginally
acceptable. If this is the case, an anisotropy of the primary emission seems
the best explanation. On the contrary, in Mrk335 we find a very large iron line
EW but a reflection component not accordingly large. In this case, the best
solution seems to be in terms of reflection from an ionized disc.


title: The beaming pattern and spectrum of inverse Compton radiation in blazars

abstract:
  By including Klein-Nishina effects, we generalize previous calculations of
the beaming pattern of photons produced by inverse Compton scattering. For an
isotropic distribution of soft photons upscattered by nonthermal electrons with
a power-law density distribution embedded in a plasma moving with relativistic
bulk speed we show that the observed radiation intensity is proportional to
D^(3+p), where D is the Doppler boosting factor, and p the electron
distribution index. This agrees with previous computations performed in the
Thomson limit, where the observed spectral index is a=(p-1)/2 and the beaming
pattern D^(4+2a). Independent of D, Klein-Nishina effects limit the location of
the peak energy of the observed spectral energy distribution such that e_{peak}
less than 1/e_0, where e_0 is the energy of the seed photons in units of mc^2.
Assuming that the seed photons originate in the broad line region, we
demonstrate that the GeV emission of blazars is significantly modified by
Klein-Nishina effects, the spectrum being softer than that calculated in the
Thomson limit. We further show that the change in spectral index of the inverse
Compton emission across the peak energy can exceed the value of 0.5 predicted
by computations performed in the Thomson limit. The model spectra agree with
OSSE and COMPTEL limits on this break without invoking the effects of
differential absorption at the edge of a gamma-ray photosphere.


title:
Implications of O and Mg abundances in metal-poor halo stars for stellar
  iron yields

abstract:
  Inhomogeneous chemical evolution models of galaxies which try to reproduce
the scatter seen in element-to-iron ratios of metal-poor halo stars are heavily
dependent on theoretical nucleosynthesis yields of core-collapse supernovae.
Hence inhomogeneous models present themselves as a test for stellar nucleosyn-
thesis calculations. Applying an inhomogeneous chemical evolution model to our
Galaxy reveals a number of shortcomings of existing theoretical nucleosynthesis
yields. One problem is the predicted scatter in [O/Fe] and [Mg/Fe] which is too
large compared to the one observed in metal-poor halo stars. This can be either
due to the O or Mg yields or due to the Fe yields (or both). However, O and Mg
are alpha-elements that are produced mainly during hydrostatic burning and thus
are not affected by the theoretical uncertainties afflicting the collapse and
explosion of a massive star. Stellar iron yields, on the other hand, depend
heavily on the choice of the mass-cut between ejecta and proto neutron star and
are therefore very uncertain. We present Fe yield distributions as function of
progenitor mass that are consistent with the abundance distribution of metal-
poor halo stars and are in agreement with observed Ni yields of SNe II with
known progenitor masses. The iron yields of lower-mass SNe II (in the range
10-20 Msol) are well constrained by those observations. Present observations,
however, do not allow to determine a unique solution for higher-mass SNe.
Nevertheless, the main dependence of the stellar iron yield as function of
progenitor mass may be derived and can be used as constraint for future
supernova/hypernova models. The results are of importance for the earliest
stages of galaxy formation when the ISM is dominated by chemical
inhomogeneities and the instantaneous mixing approximation is not valid.


title: Rotating Skyrmion Stars

abstract:
  In a previous paper, using an equation of state of dense matter representing
a fluid of Skyrmions we constructed the corresponding non-rotating compact-star
models in hydrostatic equilibrium; these are mostly fluid stars (the Skyrmion
fluid) thus naming them {\it Skyrmion Stars}.
  Here we generalize our previous calculations by constructing equilibrium
sequences of rotating Skyrmion stars in general relativity using the computer
code {\it RNS} developed by Stergioulas. We calculated their masses and radii
to be 0.4 \le M/M_{\odot} \le 3.45, and 13.0 {\rm km}\le R\le 23.0 {\rm km},
respectively (R being the circumferential radius of the star). The period of
the maximally rotating Skyrmion stars is calculated to be 0.8 {\rm ms}\le P \le
2.0 {\rm ms}. We find that a gap (the height between the star surface and the
inner stable circular orbit) starts to appear for M\sim 2.0M_{\odot}.
Specifically, the Skyrmion star mass range with an existing gap is calculated
to be 1.8 < M/ M_{\odot} < 3.0 with the corresponding orbital frequency 0.8
{\rm kHz} < \nu_{\rm ISCO} < 1.3 {\rm kHz}. We apply our model to the 4U
1820-30 low mass X-ray binary and suggest a plausible Skyrmion star candidate
in the 4U 1636-53 system. We discuss the difficulties encountered by our model
in the 4U 0614+09 case with the highest known Quasi-Periodic Oscillation
frequency of 1329 Hz. A comparative study of Skyrmion stars and models of
neutron stars based on recent/modern equations of state is also presented.


title:
Absolute kinematics of radio source components in the complete S5 polar
  cap sample I. First and second epoch maps at 8.4 GHz

abstract:
  We observed the thirteen extragalactic radio sources of the S5 polar cap
sample at 8.4 GHz with the Very Long Baseline Array, on 1997.93 and 1999.41. We
present the maps from those two epochs and briefly discuss the morphological
changes experimented by some of the radio sources in the 1.4 yr elapsed. These
results correspond to the first two epochs at 8.4 GHz of a program directed to
study the absolute kinematics of the radio source components of the members of
the sample by means of phase delay astrometry at 8.4, 15 and 43 GHz.


title:
Large scale ionization of the Radio Arc region by the Quintuplet and the
  Arches cluster

abstract:
  (Short version) We present an analysis of selected fine structure lines
observed ISO toward the Radio Arc in the Galactic center region (GCR). We study
the density of the ionized gas and the large scale ionization structure in a
region of ~30x30 pc^2 by means of the NeIII 15.6 mum/NeII 12.8 mum and NIII 57
mum/NII 122 mum line ratios. The electron densities (n_e) derived from the OIII
lines ratio indicate the presence of diffuse ionized material with n_e of
\~10^{1.8-2.6} cm^{-3}. The NIII/NII ratio show two clear gradients, one
pointing toward the Quintuplet cluster and the other pointing toward the Arches
cluster. The model used to explain the ionization structure shows that the
large scale ionization of the whole region can be accounted for by the UV
radiation produced by the Quintuplet and the Arches cluster. Any other
ionization mechanism should play a minor role. We also investigate the
influence of the clusters on the bubble of warm dust seen in the MSX infrared
images. The warm dust is well correlated with the ionized gas indicating that
the dust is also heated by the radiation from both clusters. Furthermore, the
elliptical rather than circular symmetry of some structures like the Thermal
Filaments can also be explained when one considers the combined effects of both
the Arches and the Quintuplet clusters. The bubble is filled with continuum
emission of hard X rays and with emision from the 6.4 keV line of neutral or
low ionized Fe.


title: QSO hosts and companions at higher redshifts

abstract:
  This review presents the current state of work on QSO hosts and companions at
redshifts above 1. This includes the properties of QSO host galaxies, such as
size, scale length, and luminosity, and morphology, as they appear to change
with redshift and radio activity. This leads to a view of how the properties of
galaxies that host QSOs change with cosmic time. I also review studies of the
galaxy companions to QSOs at higher redshifts, and studies of the emission line
gas in and around higher redshift QSOs. These topics should see great progress
in the next decade.


title:
A photometric and spectroscopic study of dwarf and giant galaxies in the
  Coma cluster -- III. Spectral ages and metallicities

abstract:
  (abr.) We present the analysis of the spectroscopic catalog of galaxies in
the Coma cluster from Mobasher et al. This catalog comprises ~300 spectra of
cluster members with magnitudes M_B=-20.5 to -14 in two areas of ~1 X 1.5 Mpc
towards the center and the SW region of the cluster. In this paper the analysis
is restricted to the 257 galaxies with no emission lines in their spectra. The
strength of the age-sensitive indices is found to correlate with galaxy
magnitude over the whole magnitude range. Similarly, the metallicity-sensitive
indices anticorrelate with magnitude. By comparing the observed indices with
model grids based on the Padova isochrones, we derive luminosity-weighted ages
and metallicities. We present the distributions of ages and metallicities for
galaxies in various magnitude bins. The mean metallicity decreases with galaxy
magnitude and, at a given luminosity, appears to be generally lower for
galaxies in the SW region of Coma as compared to the center of the cluster. A
broad range of ages, from younger than 3 Gyr to older than 9 Gyr, is found in
galaxies of any magnitude. However, systematic trends of age with luminosity
are present among galaxies in the central field. In the central Mpc of Coma, a
large fraction of galaxies at any luminosity (50-60% of the giants, >30 % of
the dwarfs) show no evidence in their central regions of star formation
occurred at redshift z<2, while the proportion of galaxies with significant
star formation occurring at intermediate (0.35<z<2) and low (z<0.35) redshifts
is found to depend on galaxy luminosity. Faint galaxies with young
luminosity-weighted ages appear to have a bimodal metallicity distribution
that, if confirmed, would point to a composite formation scenario. Finally, we
present an interpretation of the index-magnitude relations observed.


title:
VLBA Observations and Effelsberg Monitoring of a Flaring Water Maser in
  Mrk 348

abstract:
  We report on single-dish monitoring as well as extremely high angular
resolution observations of the flaring H2O maser in the Seyfert 2 galaxy Mrk
348. The H2O line is redshifted by ~130 km/s with respect to the systemic
velocity, is very broad, with a FWHM of 130 km/s, and has no detectable high
velocity components within 1500 km/s on either side of the strong line.
Monitoring observations made with the Effelsberg 100m telescope show that the
maser varies significantly on timescales as short as one day. VLBA observations
indicate that the maser emission arises entirely from a region less than 0.25
pc in extent, located toward a continuum component thought to be associated
with the receding jet.


title: Continuous stellar mass-loss in N-body models of galaxies

abstract:
  We present an N-body computer code - aimed at studies of galactic dynamics -
with a CPU-efficient algorithm for a continuous (i.e. time-dependent) stellar
mass-loss. First, we summarize available data on stellar mass-loss and derive
the long-term (20 Gyr) dependence of mass-loss rate of a coeval stellar
population. We then implement it, through a simple parametric form, into a
particle-mesh code with stellar and gaseous particles. We perform several tests
of the algorithm reliability and show an illustrative application: a 2D
simulation of a disk galaxy, starting as purely stellar but evolving as
two-component due to gradual mass-loss from initial stars and due to star
formation. In a subsequent paper we will use the code to study what changes are
induced in galactic disks by the continuous gas recycling compared to the
instantaneous recycling approximation, especially the changes in star formation
rate and radial inflow of matter.


title: A possible X-ray jet from the starburst galaxy NGC6217

abstract:
  Deep ROSAT PSPC and HRI observations of the nuclear starburst, UV flat
spectrum spiral NGC6217 reveal a jet-like X-ray filament extending out 2.7'
(18.8 kpc) to the SW of the galaxy. Radio images of NGC6217 show an extent in
the same direction, giving further evidence for a one-sided X-ray jet
interpretation of this feature. It's X-ray spectrum is harder than that of
NGC6217 and the luminosity in the 0.5-2.0 keV band ~1.7 E39 erg\s. We compare
our findings to parameters of other X-ray jets from other active galaxies. We
also give positions of a total of 91 X-ray sources detected in the field to a
limiting 0.5-2.0 keV flux of ~2.2E-15 erg\cm**2\s and propose optical and radio
identifications. Some of these sources have been identified in the RIXOS
program.


title: Remarks on the Theory of Cosmological Perturbation

abstract:
  It is shown that the power spectrum defined in the Synchronous Gauge can not
be directly used to calculate the predictions of cosmological models on the
large-scale structure of universe, which should be calculated directly by a
suitable gauge-invariant power spectrum or the power spectrum defined in the
Newtonian Gauge.


title: The z=5.8 Quasar SDSSp J1044-0125: A Peek at Quasar Evolution?

abstract:
  The newly discovered z=5.8 quasar SDSSp J104433.04-012502.2 was recently
detected in X-rays and found to be extremely X-ray weak. Here we present the
hardness ratio analysis of the XMM-Newton observation. We consider various
models to explain the detection in the soft X-ray band and non-detection in the
hard band, together with its X-ray weakness. We show that the source may have a
steep power-law slope, with an absorber partially covering the continuum. This
may be X-ray evidence to support the argument of Mathur (2000) that narrow line
Seyfert 1 galaxies, which show steep power-law slopes, might be the low
redshift, low luminosity analogues of the high redshift quasars. Heavily
shrouded and steep X-ray spectrum quasars may indeed represent the early stages
of quasar evolution (Mathur 2000, Fabian 1999) and SDSSp J104433.04-012502.2 is
possibly giving us a first glimpse of the physical evolution of quasar
properties.


title: Old Stellar Populations of the Small Magellanic Cloud

abstract:
  We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field
in the outer SMC. For NGC 121, we measure a true distance modulus of (m-M)0 =
18.96 +/- 0.04 (distance of 61.9 +/- 1.1 kpc), age of 10.6 +/- 0.5 Gyr,
metallicity of [Fe/H] = -1.03 +/- 0.06, and initial mass of 4.1 +/- 0.4 x 10^5
Msun, assuming a Salpeter IMF with lower cutoff at 0.1 Msun. In the outer SMC
field, we find evidence of stars covering a wide range of ages -- from 2 Gyr
old to at least 9-12 Gyr old. We have measured the distance, extinction, and
star formation history (past star formation rates and enrichment history) using
a CMD fitting algorithm. The distance modulus of the SMC is measured to be
(m-M)0 = 18.88 +/- 0.08, corresponding to a distance of 59.7 +/- 2.2 kpc. The
overall star formation rate appears to have been relatively constant over this
period, although there may be small gaps in the star forming activity too small
to be resolved. The lack of current star-forming activity is a selection
effect, as the field was intentionally chosen to avoid recent activity. The
mean metallicity of this field has increased from an average of [Fe/H] = -1.3
+/- 0.3 for stars older than 8 Gyr to [Fe/H] = -0.7 +/- 0.2 in the past 3 Gyr.


title: HI in the shell elliptical NGC 3656

abstract:
  VLA neutral hydrogen observations of the shell elliptical NGC 3656 reveal an
edge-on, warped minor axis gaseous disk (M_HI ~ 2.10^9 Msun) extending 7 kpc.
HI is also found outside the optical image, on two complexes to the North-East
and North-West that seem to trace an outer broken HI disk or ring, or possibly
one or two tidal tails.
  Integral-field optical fiber spectroscopy at the region of the bright
southern shell of NGC 3656 has provided a determination of the stellar
velocities of the shell. The shell has traces of HI with velocities bracketing
the stellar velocities, providing evidence for a dynamical association of HI
and stars at the shell. Within the errors the stars have systemic velocity,
suggesting a possible phase wrapping origin for the shell.
  We detect five dwarf galaxies with HI masses ranging from 2.10^8 Msun to
2.10^9 Msun all within 180 kpc from NGC 3656 and all within the velocity range
(450 \kms) of the HI of NGC 3656. For the NGC 3656 group to be bound requires a
total mass of 3-7.4x10^{12} Msun, yielding a mass to light ratio from 125 to
300.
  The overall HI picture presented by NGC 3656 supports the hypothesis of a
disk-disk merger origin, or possibly an ongoing process of multiple merger with
nearby dwarfs.


title: Discovery of Pulsed X-rays from the SMC Transient RX J0052.1-7319

abstract:
  Coherent 65 mHz pulsations in the X-ray flux of the Small Magellantic Cloud
(SMC) transient source RX J0052.1-7319 have been detected by us in an analysis
of ROSAT data. We report on the pulsations we detected in ROSAT HRI data and
simultaneous detection of these pulses in hard X-rays using BATSE data. The
BATSE data show an outburst of the source lasting 60 days. We report on optical
observations of the candidate companion, and a new source position we
determined from the HRI data, which is consistent with the candidate's
location. From the measured fluxes and observed frequency derivatives we
exclude the possiblity that the pulsar is in the foreground of the SMC, and
show that an accretion disk is present during the outburst, which peaked near
Eddington luminosity.


title: Heating of Gas in Galaxy Groups and Clusters

abstract:
  Was the diffuse gas in galaxy groups and clusters heated at high redshift
before it entered a massive halo, or was the heating produced inside collapsed
objects by SNII accompanying normal star formation? We compare here two
radically different models corresponding to the two scenarios described above.
Our results indicate that internal heating by SNII works better than the
extreme version of external heating that we adopt in reproducing the observed
L-T and entropy-T relations.


title: 'Stable' QPOs and Black Hole Properties from Diskoseismology

abstract:
  We compare our calculations of the frequencies of the fundamental g, c, and
p--modes of relativistic thin accretion disks with recent observations of high
frequency QPOs in X-ray binaries with black hole candidates. These classes of
modes encompass all adiabatic perturbations of such disks. The frequencies of
these modes depend mainly on only the mass and angular momentum of the black
hole; their weak dependence on disk luminosity is also explicitly indicated.
Identifying the recently discovered relatively stable QPO pairs with the
fundamental g and c modes provides a determination of the mass and angular
momentum of the black hole. For GRO J1655-40, $M=5.9\pm 1.0 M_\sun$,
$J=(0.917\pm 0.024)GM^2/c$, in agreement with spectroscopic mass
determinations. For GRS 1915+105, $M=42.4\pm 7.0 M_\sun$, $J=(0.926\pm
0.020)GM^2/c$ or (less favored) $M=18.2\pm 3.1 M_\sun$, $J=(0.701\pm
0.043)GM^2/c$. We briefly address the issues of the amplitude, frequency width,
and energy dependence of these QPOs.


title: Experimental hints of Gravity in Large Extra Dimensions?

abstract:
  Recent conjectures suggest the universe may have large extra dimensions,
through which gravity propagates. This implies gross departures from Newton's
law of gravity at small length scales. Here I consider some implications for
particle dynamics on scales comparable to the compactification radius, $R_c
\ltorder 1$ mm. During planet formation, coalescence of micron sized dust
grains to planetesimals is a rate critical step. Blum et al (2000) found dust
grain aggregates form low fractal dimension structures in microgravity,
consistent with high angular momentum coalescence. I consider the effects of
non-Newtonian gravity on dust aggregation on scales less than $R_c$ and show
they naturally coalesce into low dimensional structures with high specific
angular momentum. We infer $R_c \approx 80$ microns.


title:
Multi-wavelength observations of the Soft Gamma Repeater SGR 1900+14
  during its April 2001 activation

abstract:
  The soft-gamma repeater SGR 1900+14 became active on 18 April 2001 after
about two years of quiescence; it had remained at a very low state of activity
since the fall of 1998, when it exhibited extraordinary flaring. We have
observed the source in the gamma and X rays with Ulysses and Chandra, and in
the radio with MERLIN. We report here the confirmation of a two component X-ray
spectrum (power law + blackbody), indicating emission from the neutron star
surface. We have determined that there is a dust halo surrounding the source
that extends up to >~ 100'' from the center of SGR 1900+14, due to scattering
in the interstellar medium.


title: O(N) quintessence

abstract:
  We study a new class of quintessence models, in which the scalar field
possesses a O(\textit{N}) internal symmetry. We give a critical condition of
instability for the potential against Q ball formation. We find that the most
widely used potentials of quintessence don't satisfy the above condition, and
therefore the O(\textit{N}) quintessence with these potential will not lead to
the Q ball formation. It is worth noting that O(\textit{N}) quintessence with
cosine-type potential is especially interesting in that the angular
contribution is not negligible.


title:
The 12C(alpha,gamma)16O Reaction Rate and the Evolution of Stars in the
  Mass Range 0.8 < M/M(sun) < 25

abstract:
  We discuss the influence of the 12C(alpha,gamma)16O$ reaction rate on the
central He burning of stars in the mass range 0.8-25 Msun, as well as its
effects on the explosive yields of a 25 Msun star of solar chemical
composition. We find that the central He burning is only marginally affected by
a change in this cross section within the currently accepted uncertainty range.
The only (important) quantity which varies significantly is the amount of C
left by the He burning. Since the C(alpha,gamma)16O is efficient in a
convective core, we have also analyzed the influence of the convective mixing
in determining the final C abundance left by the central He burning. Our main
finding is that the adopted mixing scheme does not influence the final C
abundance provided the outer border of the convective core remains essentially
fixed (in mass) when the central He abundance drops below about 0.1 dex by mass
fraction; vice versa, even a slight shift (in mass) of the border of the
convective core during the last part of the central He burning could
appreciably alter the final C abundance. Hence, we stress that it is wiser to
discuss the advanced evolutionary phases as a function of the C abundance left
by the He burning rather than as a function of the efficiency of the
12C(alpha,gamma)16O reaction rate. Only a better knowledge of this cross
section and/or the physics of the convective motions could help in removing the
degeneracy between these two components. We also prolonged the evolution of the
two 25 M_sun stellar models up to the core collapse and computed the final
explosive yields.


title: COMPTEL Observations of the Blazars 3C 454.3 and CTA 102

abstract:
  We have analyzed the two blazars of 3C 454.3 and CTA 102 using all available
COMPTEL data from 1991 to 1999. In the 10-30 MeV band, emission from the
general direction of the sources is found at the 4$\sigma$-level, being
consistent with contributions from both sources. Below 10 MeV only 3C 454.3 is
significantly detected, with the strongest evidence (5.6 $\sigma$) in the 3-10
MeV band. Significant flux variability is not observed for both sources, while
a low emission is seen most of the years in the 3-10 MeV light curve for 3C
454.3. Its time-averaged MeV spectrum suggests a power maximum between 3 to 10
MeV.


title:
Search for point sources and diffuse emission from the Galactic plane
  with the HEGRA-IACT-system

abstract:
  The HEGRA-IACT-system with a FoV of ~1.5 deg radius has been used for
surveying one quater of the Galactic disc in respect to point sources,
moderately extended sources and for diffuse emission in the energy range above
1 TeV. In total 140 h of good observation time were accumulated.
  No new source has been discoverd. Limits on the level of 20% or lower of the
Crab flux on about 87 potential sources like SNR, Pulsars and EGRET sources are
derived. A limit on the diffuse emission is given on the level of dPhi/dE(E=1
TeV) = 6.1 10^-15 ph cm-2 s-1 sr-1 Mev-1 resulting in a lower limit of 2.5 on
the spectral index for the extrapolation of the meassured EGRET flux for the
diffuse emission.


title: X-Ray Observations of the supernova remnant G21.5-0.9

abstract:
  We present the analysis of archival X-ray observations of the supernova
remnant (SNR) G21.5-0.9. Based on its morphology and spectral properties,
G21.5-0.9 has been classified as a Crab-like SNR. In their early analysis of
the CHANDRA calibration data, Slane et al. (2000) discovered a
low-surface-brightness, extended emission. They interpreted this component as
the blast wave formed in the supernova (SN) explosion. In this paper, we
present the CHANDRA analysis using a total exposure of ~150 ksec. We also
include ROSAT and ASCA observations. Our analysis indicates that the extended
emission is non-thermal -- a result in agreement with XMM observations. The
entire remnant of radius ~ 2'.5 is best fitted with a power law model with a
photon index steepening away from the center. The total unabsorbed flux in the
0.5-10 keV is 1.1E-10 erg/cm2/s with an 85% contribution from the 40" radius
inner core. Timing analysis of the High-Resolution Camera (HRC) data failed to
detect any pulsations. We put a 16% upper limit on the pulsed fraction. We
derive the physical parameters of the putative pulsar and compare them with
those of other plerions (such as the Crab and 3C 58). G21.5-0.9 remains the
only plerion whose size in X-rays is bigger than in the radio. Deep radio
observations will address this puzzle.


title: Slowly rotating superfluid Newtonian neutron star model with entrainment

abstract:
  We develop a formalism to model slowly rotating superfluid Newtonian neutron
stars. A two-fluid model is used to describe the matter, where one fluid is the
superfluid neutrons that are believed to exist in the inner crust and core of
mature neutron stars, while the other fluid is a charge neutral conglomerate of
the remaining constituents (crust nuclei, core superconducting protons,
electrons, etc). We include the entrainment effect, which is a non-dissipative
interaction between the two fluids whereby a momentum induced in one of the
fluids will cause part of the mass of the other fluid to be carried along. The
equations that describe rotational equilibria (i.e. axisymmetric and stationary
configurations) are approximated using the slow-rotation approximation; an
expansion in terms of the rotation rates of the two fluids where only terms up
to second-order are kept. Our formalism allows the neutrons to rotate at a rate
different from that of the charged constituents. For a particular equation of
state that is quadratic in the two mass-densities and relative velocities of
the fluids, we find an analytic solution to the slow-rotation equations. This
result provides an elegant generalisation to the two-fluid problem of the
standard expressions for the one-fluid polytrope ${\cal E} \propto \rho^2$. The
model equation of state includes entrainment and is general enough to allow for
realistic values for, say, mass and radius of the star. It also includes a term
that can be related to ``symmetry energy'' terms that appear in more realistic
equations of state. We use the analytic solution to explore how relative
rotation between the two fluids, the ``symmetry energy'' term, and entrainment
affect the neutron star's local distribution of particles, as well as global
quantities as the Kepler limit, ellipticity, and moments of inertia.


title:
The Distribution of Thermal Pressures in the Interstellar Medium from a
  Survey of C I Fine-Structure Excitation

abstract:
  We used the smallest entrance aperture (0.03 arc-sec wide slit) and highest
resolution echelle gratings (E140H and E230H) of STIS on HST to record the
interstellar absorption features for 10 different multiplets of neutral carbon
at a wavelength resolving power of 200,000 in the UV spectra of 21 early-type
stars. We measured the amount of C I in each of its three fine-structure
levels, so that we could determine nT of the absorbing gas and how much it
varies in different regions. To obtain internally consistent results for all
multiplets, we had to modify the transition f-values so that generally weak
transitions were stronger than their published values. The fine-structure
populations indicate that the median thermal pressure for our entire sample is
p/k=2240 cm^-3 K, or slightly higher for temperatures that differ appreciably
from 40 K. About 15% of the gas moving at peculiar velocities shows p/k > 10^4
cm^-3 K, and this fraction drops to 1.5% for quiescent gas. Often, there are
small amounts of gas at p/k > 10^5 cm^-3 K. These ubiquitous wisps of high
pressure material probably arise from small-scale density enhancements created
by converging flows in a turbulent medium. The C I excitations indicate a
barytropic index gamma_eff > 0.90 when the gas is compressed, which is larger
than the value 0.72 expected for material in thermal equilibrium. This
indicates that the regions have a dimension r < 0.01 pc which allows them to
compress very quickly and nearly adiabatically. Appendices of this paper
present evidence that STIS can indeed achieve R = 200,000, and that telluric
oxygen absorption lines are broadened by macroscopic motions.


title: The confusion limit on astrometry with SIM

abstract:
  An important requirement for the Space Interferometry Mission (SIM) is to
carry out precision astrometry in crowded fields. This capability is crucial,
for example, to accurately measure proper motions of bright stars in nearby
galaxies. From such measurements, one can obtain distance estimates, explore
the dynamics of these systems and measure the mass of the Milky Way itself. In
this paper we investigate errors introduced by confusion, i.e. the presence of
objects other than the targeted star in the SIM field of view (FOV). Using
existing HST images of fields in M31, the LMC and the Galaxy we simulate the
background within the SIM FOV and estimate the errors in the measured position
of the target star. Our simulations account for the error contribution from
photon statistics. We also study the effects of pointing imperfections when a
field is revisited which result in errors in the measured proper motion. We use
the simulations to explore the measurement accuracy of several SIM key programs
which will require crowded field astrometry. In M31, the error in the absolute
position of the targets could be significant for all but the brightest targets.
Our results also indicate that in the case of the brightest targets in M31, and
for all likely target magnitudes in the other cases, confusion-induced proper
motion errors are well within the SIM requirements. However, targets which vary
in flux between measurements can be susceptible to enhanced proper motion
errors. We also find that for an on-source integration time of one hour, photon
noise is larger than or of comparable magnitude to the confusion-induced
position error for bright targets and dominates over proper motion error in
most cases.


title: Morphology of AGN in the central kiloparsec

abstract:
  Hubble Space Telescope observations of the central kiloparsec of AGN have
revealed a wealth of structure, particularly nuclear bars and spirals, that are
distinct from analogous features in the disks of spiral galaxies. WFPC2 and
NICMOS images of a large sample of AGN observed at high spatial resolution make
it possible to quantify the frequency and detailed properties of these
structures. Nearly all AGN have nuclear spiral dust lanes in the central
kiloparsec, while only a small minority contain nuclear bars. If these nuclear
dust spirals trace shocks in the circumnuclear, gaseous disks, they may
dissipate sufficient angular momentum to fuel the active nucleus.


title:
PSR J1016-5857: a young radio pulsar with possible supernova remnant,
  X-ray, and gamma-ray associations

abstract:
  We report the discovery of a young and energetic pulsar in the Parkes
multibeam survey of the Galactic plane. PSR J1016-5857 has a rotation period of
107 ms and period derivative of 8e-14, implying a characteristic age of 21 kyr
and spin-down luminosity of 2.6e36 erg/s. The pulsar is located just outside,
and possibly interacting with, the shell supernova remnant G284.3-1.8. Archival
X-ray data show a source near the pulsar position which is consistent with
emission from a pulsar wind nebula. The pulsar is also located inside the error
box of the unidentified EGRET source 3EG J1013-5915, for which it represents a
plausible counterpart.


title: Clusters of Extragalactic Ultra Compact HII Regions

abstract:
  We report on the detection of optically thick free-free radio sources in the
galaxies M33, NGC 253, and NGC 6946 using data in the literature. We interpret
these sources as being young, embedded star birth regions, which are likely to
be clusters of ultracompact HII regions. All 35 of the sources presented in
this article have positive radio spectral indices alpha>0 suggesting an
optically thick thermal bremsstrahlung emission arising in the HII region
surrounding hot stars. Energy requirements indicate a range of a several to
>500 O7V star equivalents powering each HII region. Assuming a Salpeter IMF,
this corresponds to integrated stellar masses of 0.1--60,000 Msun. For roughly
half of the sources in our sample, there is no obvious optical counterpart,
giving further support for their deeply embedded nature. Their luminosities and
radio spectral energy distributions are consistent with HII regions having
electron densities from 1500 cm^-3 to 15000 cm^-3 and radii of 1 - 7 pc. We
suggest that the less luminous of these sources are extragalactic ultracompact
HII region complexes, those of intermediate luminosity are similar to W49 in
the Galaxy, while the brightest will be counterparts to 30 Doradus. These
objects constitute the lower mass range of extragalactic ``ultradense HII
regions'' which we argue are the youngest stages of massive star cluster
formation yet observed. This sample is beginning to fill in the continuum of
objects between small associations of ultracompact HII regions and the massive
extragalactic clusters that may evolve into globular clusters.


title: Extreme BAL Quasars from the Sloan Digital Sky Survey

abstract:
  The Sloan Digital Sky Survey has discovered a population of broad absorption
line quasars with various extreme properties. Many show absorption from
metastable states of FeII with varying excitations; several objects are almost
completely absorbed bluewards of MgII; at least one shows stronger absorption
from FeIII than FeII, indicating temperatures T>35000 K in the absorbing
region; and one object even seems to have broad H-beta absorption. Many of
these extreme BALs are also heavily reddened, though `normal' BALs
(particularly LoBALs) from SDSS also show evidence for internal reddening.


title: Grains in Photo-Ionized Environments

abstract:
  Ever since the pioneering study of Spitzer, it has been widely recognized
that grains play an important role in the heating and cooling of photo-ionized
environments. This includes the diffuse ISM, as well as H II regions, planetary
nebulae, and photo-dissociation regions.
  A detailed code is necessary to model grains in a photo-ionized medium since
the interactions of grains with their environment include a host of
microphysical processes, and their importance can only be judged by performing
a complete simulation. In this paper we will use the spectral synthesis code
Cloudy for this purpose. A comprehensive upgrade of the grain model has been
recently incorporated in Cloudy, and certain aspects of this upgrade will be
discussed. Special emphasis will be on the new grain charge model. We will
consider in detail the physics of grains in both ionized and neutral
environments, and will present a calculation of photo-electric heating and
collisional cooling rates for a range of physical conditions and grain
materials and for a range of grain sizes (including a realistic size
distribution). We conclude with a brief discussion of the problems currently
hampering progress in this field. The new grain model will be used to model the
silicate emission in the Ney-Allen nebula, and will help us better understand
the nature of the grains in that part of the Orion complex.


title: Properties of a Molecular Cloud in NGC 185

abstract:
  The dwarf elliptical galaxy NGC 185- the closest early-type galaxy with
detectable molecular gas- offers a unique opportunity for high angular
resolution studies of the interstellar medium in early-type galaxies. I present
interferometric images (17 pc $\times$ 14 pc resolution) of CO emission from
NGC 185. The majority of the molecular gas in NGC 185 is in one resolved cloud,
closely associated with dust and an HI structure which may be a
photodissociated envelope. The high spatial resolution also reveals a velocity
gradient across the cloud, which allows a dynamical mass estimate independent
of the H2/CO conversion factor or the virial theorem. The linear sizes,
velocity gradients, and dynamical masses of the molecular clouds in NGC 185 and
NGC 205, a similar dwarf elliptical, are comparable to those of the largest
Galactic giant molecular clouds (GMCs). If the dynamical masses of the clouds
are assumed to be good estimates of their true masses, the inferred H2/CO
conversion factor in NGC 185 is at least eight times larger than a standard
Galactic conversion factor, and the reasons for this difference are not yet
understood. In any case, it seems clear that structures similar to Galactic
GMCs can form in small elliptical or early type galaxies, even in the absence
of spiral density waves.


title: On the Normalization of the QSO's Lyman alpha Forest Power Spectrum

abstract:
  The calculation of the transmission power spectrum of QSO's Lyman alpha
absorption requires two parameters for the normalization: the continuum Fc and
mean transmission, i.e. average of e^{-tau}. Traditionally, the continuum is
obtained by a polynomial fitting truncating it at a lower order, and the mean
transmission is calculated over the entire wavelength range considered. The
flux F is then normalized by the average of Fc e^{-tau}. However, the
fluctuations in the transmitted flux are significantly correlated with the
local background flux on scales for which the field is intermittent. In this
paper, we develop a self-normalization algorithm of the transmission power
spectrum based on a multiresolution analysis. This self-normalized power
spectrum estimator needs neither a continuum fitting, nor pre-determining the
mean transmission. With simulated samples, we show that the self-normalization
algorithm can perfectly recover the transmission power spectrum from the flux
regardless of how the continuum varies with wavelength. We also show that the
self-normalized power spectrum is also properly normalized by the mean
transmission. Moreover, this power spectrum estimator is sensitive to the
non-linear behavior of the field. That is, the self-normalized power spectrum
estimator can distinguish between fields with or without the
fluctuation-background correlation. This cannot be accomplished by the power
spectrum with the normalization by an overall mean transmission. Therefore, the
self-normalized power spectrum would be useful for the discrimination among
models without the uncertainties caused by free (or fitting) parameters.


title:
Ultraviolet Spectrophotometry of Variable Early-Type Be and B stars
  Derived from High-Resolution IUE Data

abstract:
  High-dispersion IUE data encode significant information about aggregate line
absorptions that cannot be conveniently extracted from individual spectra. We
apply a new technique in which fluxes from each echelle order of a short
wavelength IUE spectrum are binned together to construct low-resolution spectra
of a rapidly varying B or Be star. The ratio of binned spectra obtained bright-
star and faint-star phases contains information about the mechanism responsible
for a star's variability, such as from pulsations or occultations of the star
by ejected matter. We model the variations caused by these mechanism by means
of model atmosphere and absorbing-slab codes. Line absorptions strength changes
are sensitive to conditions in circumstellar clouds with T = 8,000--13,000K. To
demonstrate proofs of concept, we construct spectral ratios for circumstellar
structures associated with flux variability in various Be stars: (1) Vela X1
has bow-shock wind trailing its neutron star companion and shows signatures of
gas at 13,000K or 26,000K medium in different sectors, (2) 88 Her undergoes
episodic outbursts as its UV flux fades, followed a year later by a dimming in
visible wavelengths, a result of a gray opacity that dominates as the shell
expands and cools, and (3) zeta Tau and 60 Cyg exhibit periodic spectrum and
flux changes, which match model absorptions for occulting clouds. Also, ratioed
UV spectra of strongly pulsating stars show unique spectrophotometric
signatures which can be simulated with models. An analysis of ratioed spectra
obtained for a typical sample of 18 classical Be stars known to have rapid
periodic flux variations indicates that 13 of them have ratioed spectra which
are relatively featureless or have signatures of pulsation. Ratioed spectra of
3 others in the sample are consistent with the presence of co-rotating clouds.


title: The Galaxy Octopole Moment as a Probe of Weak Lensing Shear Fields

abstract:
  In this paper, we introduce the octopole moment of the light distribution in
galaxies as a probe of the weak lensing shear field. While traditional
ellipticity estimates of the local shear derived from the quadrupole moment are
limited by the width of the intrinsic ellipticity distribution of background
galaxies, the dispersion in the intrinsic octopole distribution is expected to
be much smaller, implying that the signal from this higher order moment is
ultimately limited by measurement noise, and not by intrinsic scatter. We
present the computation of the octopole moment and show that current
observations are at the regime where the octopole estimates will soon be able
to contribute to the overall accuracy of the estimates of local shear fields.
Therefore, the prospects for this estimator from future datasets like the
Advanced Camera for Survey and the Next Generation Space Telescope are very
promising.


title:
Afterglow upper limits for four short duration, hard spectrum gamma-ray
  bursts

abstract:
  We present interplanetary network localization, spectral, and time history
information for four short-duration, hard spectrum gamma-ray bursts, GRB000607,
001025B, 001204, and 010119. All of these events were followed up with
sensitive radio and optical observations (the first and only such bursts to be
followed up in the radio to date), but no detections were made, demonstrating
that the short bursts do not have anomalously intense afterglows. We discuss
the upper limits, and show that the lack of observable counterparts is
consistent both with the hypothesis that the afterglow behavior of the short
bursts is like that of the long duration bursts, many of which similarly have
no detectable afterglows, as well as with the hypothesis that the short bursts
have no detectable afterglows at all. Small number statistics do not allow a
clear choice between these alternatives, but given the present detection rates
of various missions, we show that progress can be expected in the near future.


title: Temperature Bias and the Primordial Helium Abundance Determination

abstract:
  We study the effect that the temperature structure has on the determination
of the primordial helium abundance, Yp. We provide an equation linking T(OIII),
the temperature derived from the [OIII] lines, and T(HeII), the temperature of
the He I lines, both for HII regions with O++ only and for HII regions where a
fraction of O+ is present. By means of T(HeII), which is always smaller than
T(OIII), we derive the helium abundances of 5 objects with low and very low
metallicity (NGC 346, NGC 2363, Haro29, SBS 0335-052, and I Zw 18); these
objects were selected from the literature because they include the 3 low
metallicity objects with the best line determinations and the 2 objects with
the lowest metallicity. From these abundances we obtain that
Yp(nHc)=0.2356+-0.0020, a value 0.0088 lower than that derived by using
T(OIII). We call this determination Yp(nHc) because the collisional
contribution to the Balmer line intensities has not been taken into account.
All the recent Yp determinations in the literature have not taken into account
the collisional contribution to the Balmer line intensities. By considering the
collisional contribution to the Balmer line intensities of these five objects
we derive that Yp(+Hc)=0.2384+-0.0025.


title:
A contribution of 26Al to the O-Al anticorrelation in globular cluster
  red giants

abstract:
  We modify our combined ("deep mixing" plus "primordial") scenario explaining
the star-to-star abundance variations in globular cluster red giants in such a
way that it confirms with new experimental data: (i) the new and better
constrained (NACRE) thermonuclear reaction rates and (ii) a discovery of the
O-Na anticorrelation in stars below the main-sequence turn-off in the cluster
NGC6752. For the latter we propose that some main-sequence dwarfs in globular
clusters accrete material lost by red giant primary components of close
binaries during a common envelope event. As a consequence of the new reaction
rates, we are drawn to the conclusion that the anomalies in [Al/Fe] in globular
cluster red giants are in fact manifestations of 26Al (instead of the stable
isotope 27Al) abundance variations produced by deep mixing.