title: Black Holes Must Die

abstract:
  In light of recent evidence suggesting a nonzero present-day cosmological
constant, Adams, Mbonye, & Laughlin (1999) have considered the evolution of
black holes in the presence of vacuum energy. Using the assumption that Lambda
remains constant with time, and a conjecture based on a paper by Mallett
(1986), they reach the remarkable conclusion that black holes with current mass
greater than about 2*10^(-9) Msun will not Hawking evaporate in the distant
future, but will instead absorb vacuum energy and grow to roughly the de Sitter
horizon size. In this letter we reexamine black hole evaporation in the
presence of vacuum energy, and find instead that all known black holes will
eventually evaporate.


title: Polarized mm And sub-mm Emission From Sgr A* At The Galactic Center

abstract:
  The recent detection of significant linear polarization at mm and sub-mm
wavelengths in the spectrum of Sgr A* (if confirmed) will be a useful probe of
the conditions within several Schwarzschild radii ($r_S$) of the event horizon
at the Galactic Center. Hydrodynamic simulations of gas flowing in the vicinity
of this object suggest that the infalling gas circularizes when it approaches
within $5-25 r_S$ of the black hole. We suggest that the sub-mm ``excess'' of
emission seen in the spectrum of Sgr A* may be associated with radiation
produced within the inner Keplerian region and that the observed polarization
characteristics provide direct evidence for this phenomenon. The overall
spectrum from this region, including the high-energy component due to
bremsstrahlung and inverse Compton scattering processes, is at or below the
recent {\it Chandra} measurement, and may account for the X-ray source if it
turns out to be the actual counterpart to Sgr A*.


title:
Effects of dust extinction on optical spectroscopic properties for
  starburst galaxies in distant clusters

abstract:
  Recent observational studies on galaxies in distant clusters discovered a
significant fraction of possible dusty starburst galaxies with the so-called
`e(a)' spectra that are characterized by strong H$\delta$ absorption and
relatively modest [OII] emission. We numerically investigate spectroscopic and
photometric evolution of dusty starburst galaxies in order to clarify the
origin of the e(a) spectra. We found that if a young starburst population is
preferentially obscured by dust than an old one in a dusty starburst galaxy,
the galaxy shows e(a) spectrum. It is therefore confirmed that the selective
dust extinction, which is first suggested by Poggianti & Wu (2000) and means
the strongest dust extinction for the youngest stellar population among stellar
populations with different ages, is critically important to reproduce
quantitatively the observed e(a) spectra for the first time in the present
numerical study. We furthermore discuss what physical process is closely
associated with this selective dust extinction in cluster environment.


title:
Distance Constraints for High Velocity Clouds from Optical Emission
  Lines

abstract:
  We report results from a survey of high velocity clouds and the Magellanic
Stream for faint, diffuse optical recombination emission lines. We detect
H-alpha emission with surface brightness from 41 to 1680 milli-Rayleighs (mR)
from HVCs, and from <40 to 1360 mR in the MS. A simple model for the
photoionizing radiation emergent from the Galaxy, normalized to the HVCs A and
M with known distances, predicts distances from a few to 40 kpc, placing the
faintest HVCs in the Galactic halo, too far away for a Galactic fountain. This
model cannot explain the bright and spatially varying H-alpha in the Magellanic
Stream, which requires another source of ionization. However, we do not find
any HVCs super-faint in H-alpha; even with another ionization source, we
conclude that the detected HVCs are not more than 2--4 times the distance of
the MS (100-200 kpc).


title: A Statistical Study of Emission Lines from High Redshift Radio Galaxies

abstract:
  We have compiled a sample of 165 radio galaxies from the literature to study
the properties of the extended emission line regions and their interaction with
the radio source over a large range of redshift 0<z<5.2. For each source, we
have collected radio (size, lobe distance ratio and power) and spectroscopic
parameters (luminosity, line width and equivalent width) for the four brightest
UV lines. We also introduce a parameter A_{Ly-alpha} measuring the asymmetry of
the Ly-alpha line. Using these 18 parameters, we examine the statistical
significance of all 153 mutual correlations, and find the following significant
correlations: (i) Ly-alpha asymmetry A_{Ly-alpha} with radio size and redshift,
(ii) line luminosity with radio power, (iii) line luminosities of UV lines with
each other, and (iv) equivalent widths of UV lines with each other. Using
line-ratio diagnostic diagrams, we examine the ionization mechanism of the
extended emission line regions in HzRGs. The high ionization lines seem to
confirm previous results showing that AGN photo-ionization provides the best
fit to the data, but are inconsitent with the CII/CIII ratio, which favour the
highest velocity shock ionization models. We note that the CII line is 5 times
more sensitive to shock ionization than the high ionization UV lines, and show
that a combination of shock and photo-ionization provides a better overall fit
to the integrated spectra of HzRGs. Because most HzRGs have radio sizes <~150
kpc, their integrated spectra might well contain a significant contribution
from shock ionized emission. [abridged]


title: Cosmic concordance and the fine structure constant

abstract:
  Recent measurements of a peak in the angular power spectrum of the cosmic
microwave background appear to suggest that geometry of the universe is close
to being flat. But if other accepted indicators of cosmological parameters are
also correct then the best fit model is marginally closed, with the peak in the
spectrum at larger scales than in a flat universe. Such observations can be
reconciled with a flat universe if the fine structure constant had a lower
value at earlier times, which would delay the recombination of electrons and
protons and also act to suppress secondary oscillations as observed. We discuss
evidence for a few percent increase in the fine structure constant between the
time of recombination and the present.


title:
Using Perturbative Least Action to Reconstruct Redshift Space
  Distortions

abstract:
  In this paper, we present a redshift space reconstruction scheme which is
analogous to and extends the Perturbative Least Action (PLA) method described
by Goldberg & Spergel (2000). We first show that this scheme is effective in
reconstructing even nonlinear observations. We then suggest that by varying the
cosmology to minimize the quadrupole moment of a reconstructed density field,
it may be possible to lower the errorbars on the redshift distortion parameter,
$\beta$ as well as to break the degeneracy between the linear bias parameter,
$b$, and $\Omega_M$. Finally, we discuss how PLA might be applied to realistic
redshift surveys.


title: The Extreme Scattering Event Toward 1741-038: H I Absorption

abstract:
  We report multi-epoch VLA H I absorption observations of the source 1741-038
(OT-068) before and during an extreme scattering event (ESE). Observations at
four epochs, three during the ESE, were obtained. We find no changes in the
equivalent width, maximum optical depth, or velocity of maximum optical depth
during the ESE, but we do find a secular trend of decreasing maximum optical
depth between our observations and ones by other observers a decade prior. The
resulting limit on the H I column density change during the ESE for a structure
with a spin temperature T_s is 6.4 x 10^{17} cm^{-2} (T_s/10 K). Tiny-scale
atomic structures (TSAS), with a column density N_H ~ 3 x 10^{18} cm^{-2}, are
ruled out marginally by this limit, though geometric arguments may allow this
limit to be relaxed. Galactic halo molecular clouds, that are opaque in the H I
line, cannot be excluded because the observed velocity range covers only 25% of
their allowed velocity range.


title: The Effect of the (2+1)-Dimensional Gravity in the Spiral Galaxy

abstract:
  The slowly decreasing rotational velocity of the Milky Way suggests the
existence of the dark matter. One finds that the effect of the dark matter in a
galaxy can be described by a $(2+1)$-dimensional fluid model. The stability
analysis for the corresponding fluid model is discussed in details in this
paper. It is found that the pressure term plays an important role in the
stability of the spiral arms and counteracts the increasing mass of the
observed galaxy as the radial distance increases. When the fluid region ends,
the $ nearly $ constant rotational velocity of the distant stars require no
additional mass if the spatial dimension in the remote region is close to two.
This indicates that the galaxies, we are interested, could be explained by a
$(2+1)$-dimensional model. Possible implications are also discussed in this
paper.


title:
Kinematics and morphology of the Narrow-Line Region in the Seyfert
  galaxy NGC1386

abstract:
  We present a high spatial and spectral resolution 2-D echelle spectrogram of
the Narrow-Line Region in the Seyfert 2 galaxy NGC1386. This Seyfert galaxy was
observed with CASPEC in the wavelength range 5270-7725 Angstrom which covers
the H-alpha and the [N II] lines. With the use of spatially high resolved
images taken with the WFPC2 aboard the Hubble Space Telescope we could identify
individual components of the Narrow-Line Region in our spectra. A Gaussian
decomposition of the spectra revealed 9 distinct emission-line complexes. The
brightest component is blue-shifted by -120+-10 km/s with respect to the
systemic velocity and shows an offset of -1.6" relative to the nucleus of the
galaxy. The true nucleus of NGC1386 has a much lower apparent H-alpha
luminosity than this component. The nucleus is probably highly absorbed.
Although the majority of the Narrow-Line Region components follows a regular
velocity field, we find evidence for a separate kinematic component. The
Narrow-Line Region is aligned anti-parallel to the radio-jet which propagates
from the center of NGC1386 to the south.


title: Mixing through shear instabilities

abstract:
  In this paper we present the results of numerical simulations of the
Kelvin-Helmholtz instability in a stratified shear layer. This shear
instability is believed to be responsible for extra mixing in differentially
rotating stellar interiors and is the prime candidate to explain the abundance
anomalies observed in many rotating stars. All mixing prescriptions currently
in use are based on phenomenological and heuristic estimates whose validity is
often unclear. Using three-dimensional numerical simulations, we study the
mixing efficiency as a function of the Richardson number and compare our
results with some semi-analytical formalisms of mixing.


title:
Validation of Up-the-Ramp Sampling with Cosmic Ray Rejection on IR
  Detectors

abstract:
  We examine cosmic ray rejection methodology on data collected from InSb and
Si:As detectors. The application of an Up-the-Ramp sampling technique with
cosmic ray identification and mitigation is the focus of this study. This
technique is valuable for space-based observatories which are exposed to
high-radiation environments. We validate the Up-the-Ramp approach on
radiation-test data sets with InSb and Si:As detectors which were generated for
SIRTF. The Up-the-Ramp sampling method studied in this paper is over 99.9%
effective at removing cosmic rays and preserves the structure and photometric
quality of the image to well within the measurement error.


title:
Blue horizontal branch stars in metal-rich globular clusters. II. 47 Tuc
  and NGC 362

abstract:
  Atmospheric parameters (effective temperature, surface gravity) and radial
velocities are derived for 12 candidate blue horizontal branch (HB) stars in
the globular clusters 47 Tuc and NGC 362, which so far have been known to
contain primarily red HB stars. The spectroscopic targets were selected from
the catalog of hot stars detected in these clusters at 1600 A using the
Ultraviolet Imaging Telescope (UIT). Spectroscopic analyses of these stars
reveal, however, that one of the four HB candidate targets in 47 Tuc, and five
out of the eight targets in NGC 362 are probably background stars belonging to
the Small Magellanic Cloud. With the exception of the photometric binary
MJ38529 in 47 Tuc, the parameters of those stars that are probable members of
47 Tuc and NGC 362 agree well with canonical HB evolution. The three hot stars
in 47 Tuc all have 10,000 K < Teff < 15,000 K and include one photometric
binary, which suggests that they might have a different physical origin than
the dominant red HB population. The somewhat cooler blue HB stars in NGC 362
show more continuity with the dominant red HB population and might simply arise
from red giants with unusually high mass loss.


title: The Broad-Line and Narrow-Line Regions of the LINER NGC 4579

abstract:
  We report the discovery of an extremely broad H-alpha emission line in the
LINER nucleus of NGC 4579. From ground-based observations, the galaxy was
previously known to contain a Type 1 nucleus with a broad H-alpha line of FWHM
= 2300 km/s and FWZI ~ 5000 km/s. New spectra obtained with the Hubble Space
Telescope and a 0.2 arcsec-wide slit reveal an H-alpha component with FWZI ~
18,000 km/s. The line is not obviously double-peaked, but it does possess
shoulders on the red and blue sides which resemble the H-alpha profiles of
double-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggests
that the very broad H-alpha profile in NGC 4579 may represent emission from an
accretion disk. Three such objects have been found recently in two HST programs
which have targeted a total of 30 galaxies, demonstrating that double-peaked or
extremely broad-line emission in LINERs must be much more common than would be
inferred from ground-based surveys. The ratio of the narrow [S II] 6716, 6731
lines shows a pronounced gradient indicating a steep rise in density toward the
nucleus. The direct detection of a density gradient within the inner arcsecond
of the narrow-line region confirms expectations from previous observations of
linewidth-critical density correlations in several LINERs.


title: ASCA Observations of GX 354-0 and KS 1731-260

abstract:
  We report on ASCA observations of the low mass X-ray binaries GX 354-0 and KS
1731-260. The spectrum of GX 354-0 is best described as a power-law or a
Comptonized spectrum with tau ~ 5 and kT ~ 8 keV and a residual at ~6.5 keV.
The residual may be a disk reflection or a Compton broadened Gaussian line from
the hot inner ADAF-like coronal region. The absorption column density to the
source is 2.9e22 cm^-2. No soft thermal component was detected. The spectrum
from KS 1731-260 is softer and it is best fit with a two component model with a
column density of 1.1e22 cm^-2. The likely interpretation is emission from a
Comptonizing cloud with an optical depth tau>12 and either a neutron star or a
disk blackbody emission. We discuss the likely location of the Comptonizing
cloud for both sources within the context of several proposed emission models.


title: Development of Gold Contacted Flip-chip Detectors with IMARAD CZT

abstract:
  We present initial results from our evaluation of a gold-contacted pixellated
detector using cadmium zinc telluride substrate produced by IMARAD Imaging
Systems. The Horizontal Bridgman (HB) grown crystals from IMARAD have been
shown to produce high resolution photopeaks, but they are also seen to have
large leakage current. Our previous tests with IMARAD CZT showed that the use
of indium anodes and gold cathode improved the resistivity compared to the
standard indium-contacted detectors. We seek to test whether simple evaporated
gold contacts alone could also reduce the leakage current and thus improve the
spectral resolution, especially in the 10-100 keV energy range. We have
fabricated several metal-semiconductor-metal (MSM) detectors with a 4x4 array
of pixels on 10x10 mm substrates. Measurements of the detectors' leakage
current, spectral response, and temperature sensitivity are presented and
compared to IMARAD's ohmic contact detector and gold contact MSM detectors made
of High Pressure Bridgman (HPB) material. Finally, we show preliminary results
from a tiled flip-chip pixellated detector made using the IMARAD detectors.


title: Star Formation History in the Nicmos Northern Hubble Deep Field

abstract:
  This paper presents the star formation history in the NICMOS Northern Deep
HDF. It uses the techniques of photometric redshifts and extinctions to correct
for extinction of the ultra-violet flux. It presents a new method for
correcting for surface brightness diming. It also predicts the 850 micron
fluxes of the objects for comparison with SCUBA measurements


title: A New Angle on Gravitational Clustering

abstract:
  We describe a new approach to gravitational instability in large-scale
structure, where the equations of motion are written and solved as in field
theory in terms of Feynman diagrams. The basic objects of interest are the
propagator (which propagates solutions forward in time), the vertex (which
describes non-linear interactions between waves) and a source with prescribed
statistics which describes the effect of initial conditions. We show that loop
corrections renormalize these quantities, and discuss applications of this
formalism to a better understanding of gravitational instability and to
improving non-linear perturbation theory in the transition to the non-linear
regime. We also consider the role of vorticity creation due to shell-crossing
and show using N-body simulations that at small (virialized) scales the
velocity field reaches equipartition, i.e. the vorticity power spectrum is
about twice the divergence power spectrum.


title:
Protoplanetary disks around Herbig Ae/Be stars: Indications from ISO
  spectroscopy

abstract:
  An analysis of solid-state features in infrared spectra of 46 Herbig Ae/Be
stars is presented. The presence of solid-state emission bands is compared to
other indicators of circumstellar material, such as Halpha emission, optical
variability and sub-mm continuum fluxes. The correlation between these
different indicators is weak, if present at all, in our sample. However, a
strong dependence on spectral type of the central star seems to be present:
stars with spectral type earlier than B9 show either amorphous silicate in
absorption or infrared spectra dominated by PAH emission, whereas more than 70%
of the stars of later spectral type show silicate emission. We conclude that
the infrared spectrum of Herbig Be stars is in general dominated by emission
from the circumstellar envelope, whereas the lower-mass Herbig Ae stars show a
spectrum that is dominated by a disk that is passively heated by the central
star.


title: HEXTE Detections of Hard X-Ray Tails in Sco X-1

abstract:
  We report the detection of a non-thermal hard X-ray component from Sco X-1
based upon the analysis of 20-220 keV spectra obtained with the HEXTE
experiment on-board the RXTE satellite. We find that the addition of a
power-law component to a thermal bremsstrahlung model is required to achieve a
good fit in 5 of 16 observations analyzed. Using PCA data we were able to track
the movement of the source along the Z diagram, and we found that the presence
of the hard X-ray tail is not confined to a specific Z position. However, we do
observe an indication that the power law index hardens with increasing mass
accretion rate, as indicated from the position on the Z diagram. We find that
the derived non-thermal luminosities are at order of 10% of that derived for
the brightest of the atoll sources.


title:
Infrared L Band Observations of the Trapezium Cluster: A Census of
  Circumstellar Disks and Candidate Protostars

abstract:
  We report the results of a sensitive near-infrared JHKL imaging survey of the
Trapezium cluster in Orion. We use the JHKL colors to obtain a census of
infrared excess stars in the cluster. Of (391) stars brighter than 12th
magnitude in the K and L bands, 80 +/- 7% are found to exhibit detectable
infrared excess on the J-H, K-L color-color diagram. Examination of a subsample
of 285 of these stars with published spectral types yields a slightly higher
infrared excess fraction of 85%. We find that 97% of the optical proplyds in
the cluster exhibit excess in the JHKL color-color diagram indicating that the
most likely origin of the observed infrared excesses is from circumstellar
disks. We interpret these results to indicate that the fraction of stars in the
cluster with circumstellar disks is between 80-85%. Moreover, we find that the
probability of finding an infrared excess/protoplanetary disk around a star is
independent of stellar mass over essentially the entire range of the stellar
mass function down to the hydrogen burning limit. We identify 78 stars in our
sample characterized by K-L colors suggestive of deeply embedded protostellar
objects. If even a modest fraction fraction (i.e., ~ 50%) of these objects are
protostars, then star formation could be continuing in the molecular ridge at a
rate comparable to that which produced the foreground Trapezium cluster.


title:
Cosmological-Model-Parameter Determination from Satellite-Acquired Type
  Ia and IIP Supernova Data

abstract:
  We examine the constraints that satellite-acquired Type Ia and IIP supernova
apparent magnitude versus redshift data will place on cosmological model
parameters in models with and without a constant or time-variable cosmological
constant $\Lambda$. High-quality data which could be acquired in the near
future will result in tight constraints on these parameters. For example, if
all other parameters of a spatially-flat model with a constant $\Lambda$ are
known, the supernova data should constrain the non-relativistic matter density
parameter $\Omega_0$ to better than 1% (2%, 0.5%) at 1$\sigma$ with neutral
(worst case, best case) assumptions about data quality.


title:
The MACHO Project Hubble Space Telescope Follow-Up: Preliminary Results
  on the Location of the Large Magellanic Cloud Microlensing Source Stars

abstract:
  We attempt to determine whether the MACHO microlensing source stars are drawn
from the average population of the LMC or from a population behind the LMC by
examining the HST color-magnitude diagram (CMD) of microlensing source stars.
We present WFPC2 HST photometry of eight MACHO microlensing source stars and
the surrounding fields in the LMC. The microlensing source stars are identified
by deriving accurate centroids in the ground-based MACHO images using
difference image analysis (DIA) and then transforming the DIA coordinates to
the HST frame. We consider in detail a model for the background population of
source stars based on that presented by Zhao, Graff & Guhathakurta. In this
model, the source stars have an additional reddening <E(B-V)> = 0.13 mag and a
slightly larger distance modulus <Delta mu> ~ 0.3 mag than the average LMC
population. We also investigate a series of source star models, varying the
relative fraction of source stars drawn from the average and background
populations and the displacement of the background population from the LMC. Due
to the small number of analyzed events the distribution of probabilities of
different models is rather flat. A shallow maximum occurs at a fraction s_LMC ~
0.8 of the source stars in the LMC. This is consistent with the interpretation
that a significant fraction of observed microlensing events are due to lenses
in the Milky Way halo, but does not definitively exclude other models.


title: Lyman Continuum Emission from Galaxies at z~3.4

abstract:
  We report the detection of significant Lyman continuum flux in the composite
spectrum of 29 Lyman break galaxies (LBGs) with redshifts <z> = 3.40+/-0.09.
After correction for opacity due to intervening absorption using a new
composite QSO spectrum evaluated at the same redshift, the ratio of emergent
flux density at 1500 \AA in the rest frame to that in the Lyman continuum is
L(1500)/L(900) = 4.6 +/- 1.0. If the relative intensity of the inferred
escaping Lyman continuum radiation is typical of LBGs at z ~ 3 (the galaxies in
this sample are drawn from the bluest quartile of LBG spectral energy
distributions due to known selection effects), then observed LBGs produce about
5 times more H-ionizing photons per unit co-moving volume than QSOs at z ~ 3.
The associated contribution to the metagalactic ionizing radiation field is
J_{\nu}(912) = 1.2+/-0.3 x 10^{-21} ergs s^{-1} cm^{-2} Hz^{-1} sr^{-1} at z ~
3, very close to most estimates of the radiation field background based on the
``proximity effect''. A preliminary analysis of the density of faint QSOs in
our Lyman break galaxy survey indicates that the standard extrapolated QSO
luminosity function may slightly over-predict the QSO contribution to
J_{\nu}(912) at z ~ 3. We briefly discuss the implications of a
galaxy-dominated UV background at high redshifts.


title:
Construction and Testing of a Pixellated CZT Detector and Shield for a
  Hard X-ray Astronomy Balloon Flight

abstract:
  We report on the construction and laboratory testing of pixellated CZT
detectors mounted in a flip-chip, tiled fashion and read out by an ASIC, as
required for proposed hard X-ray astronomy missions. Two 10 mm x 10 mm x 5 mm
detectors were fabricated, one out of standard eV Products high-pressure
Bridgman CZT and one out of IMARAD horizontal Bridgman CZT. Each was fashioned
with a 4 x 4 array of gold pixels on a 2.5 mm pitch with a surrounding guard
ring. The detectors were mounted side by side on a carrier card, such that the
pixel pitch was preserved, and read out by a 32-channel VA-TA ASIC from IDE AS
Corp. controlled by a PC/104 single-board computer. A passive shield/collimator
surrounded by plastic scintillator encloses the detectors on five sides and
provides a ~40deg field of view. Thus this experiment tests key techniques
required for future hard X-ray survey instruments. The experiment was taken to
Ft Sumner, NM in May 2000 in preparation for a scientific balloon flight aboard
the joint Harvard-MSFC EXITE2/HERO payload. Although we did not receive a
flight opportunity, and are currently scheduled to fly in September 2000, we
present our calibration data in the flight configuration together with data
analysis techniques and simulations of the expected flight background spectrum.


title: Modern Supernova Search

abstract:
  Supernovae play a critical role in observational cosmology as well as in
astrophysics of stars and galaxies. Recent era has seen dramatic progress in
the research of supernovae. Several programs to search systematically
supernovae in nearby to distant galaxies have been very successful. Recent
progresses in the modern supernova search are reviewed.


title: Morphological Number Counts of Galaxies in the Hubble Deep Field South

abstract:
  We present a study of photometric properties of the galaxies in the Hubble
Deep Field South (HDFS) based on the released WFPC2 images obtained with the
Hubble Space Telescope (HST). We have classified about 340 galaxies with $I<26$
mag in the HDFS as well as about 400 galaxies in the Hubble Deep Field North
(HDFN) using the visual classification supplemented by inspection of the
surface brightness profiles of the galaxies. Galaxy population statistics and
morphological number counts for the HDFS are found to be similar to be those
for the HDFN. We have also determined photometrically the redshifts of the
galaxies with $I<26$ mag in the HDFS and the HDFN using the empirical training
set method. Redshift distribution, color-redshift relation, and
magnitude-redshift for each type of galaxies are investigated.


title: Cosmology with Varying Constants

abstract:
  I motivate and discuss some recent work on theories with varying constants,
and consider some possible observational consequences and tests. Particular
emphasis is given to models which can (almost) exactly mimic the predictions of
standard inflationary models.


title:
Small-scale structures in Compact Steep-Spectrum and GHz-Peaked-Spectrum
  radio sources

abstract:
  We determine the small-scale structure for a large sample of Compact Steep
Spectrum (CSS) and Gigahertz Peaked Spectrum (GPS) sources and a sample of
larger radio sources at 327 MHz using the technique of Inter-Planetary
Scintillation (IPS) with the Ooty Radio Telescope. Our observations provide
structural information on angular scales ranging from about 50 to a few hundred
milliarcsec. We estimate the size and flux density of the scintillating
components from the IPS observations. The fraction of flux density of the
hotspots estimated from both the IPS observations as well as from
interferometric observations for larger sources from the literature exhibits no
significant dependence on either the radio luminosity or linear size for the
high-luminosity sources. We examine the collimation of radio jets using the
sizes of hotspots from both IPS and interferometric observations. The hotspot
sizes do not exhibit a significant dependence on the overall linear size for
the larger sources, although the CSS and GPS sources were earlier found to
evolve in a self-similar way. The IPS observations show evidence of
larger-scale structures compared to the known VLBI-scale structures in 8 CSS
and GPS radio sources. We discuss the origin of these structures. We also
examine the spectra of compact components in GPS sources using both IPS and
interferometric measurements, and attempt to distinguish between different
processes for explaining their low-frequency spectra.


title: On the degree of dust extinction in major mergers

abstract:
  We numerically investigate how fundamental properties of the spectral energy
distribution (SED) of a major gas-rich galaxy merger with dusty starburst are
determined by the initial orbital configuration of the merger. We found that an
infrared luminous galaxy with dusty starburst formed by a nearly
retrograde-retrograde merger suffers the most remarkable dust extinction of
stellar light and consequently shows very red colors. Considering that a
retrograde-retrograde merger does not produce strong and long tidal tails, this
result suggests that a luminous infrared galaxy without clear signs of
interaction and merging shows very large internal dust extinction and redder
colors.These numerical results furthermore imply that the morphology of a
luminous infrared galaxy can correlate with the degree of internal dust
extinction and thus with the shape of the SED, principally because the
morphology of a merger also depends strongly on the initial orbital
configuration of the merger.


title: The Origins of Disk Heating

abstract:
  By making spectral absorption-line observations of disk galaxies at
intermediate inclinations, we have been able to determine the amplitude of
their constituent stars' random motions in three dimensions. This full measure
of the shape of the velocity ellipsoid is a useful diagnostic for determining
the "heating" mechanism responsible for creating the random motions. The
analysis implies that the main heating process varies with galaxy type, with
minor mergers dominating the heating in early-type disk galaxies, and spiral
density waves the most important mechanism in late-type systems.


title: The X-Ray Absorber in Broad Absorption Line Quasars

abstract:
  Recent observations of Broad Absorption Line (BAL) quasars demonstrated that
the soft X-ray emission of these objects is extremely weak and convincing
evidence for very strong absorption by a high column density (~ 10^23.5 cm^-2)
was obtained for PG 1411+442, even though it is one of the few BAL QSOs
strongly detected in soft X-rays. This paper examines the ionization status and
geometry of the X-ray absorber by combining the properties of the UV lines with
the X-ray continuum absorption. We show that the gas has to have large column
densities in ions of major UV absorption lines, such as CIV, NV, OVI and Ne
VIII, in order to have sufficient opacity around 0.2 to 0.35 keV. The UV
absorption lines have to be saturated if the X-ray absorber intersects the line
of sight to the UV continuum emission region. A uniformly covering UV and X-ray
absorption model can be constructed for PG 1411+442 but in some other soft
X-ray detected BAL QSOs, such as PG 1001+054, the observed line optical depth
is much lower than expected from the X-ray absorbing material. We propose a
scheme in which a substantial fraction of the line of sight to the continuum
source may be covered by either an optically thick flow or clouds in a narrow
velocity range, but in which the total covering factor of either the whole flow
or all clouds is close to unity.


title: Observational signatures of X-ray irradiated accretion disks

abstract:
  Reflection of X-rays from cool material around a black hole is one of the few
observational diagnostics of the accretion flow geometry. Models of this
reflected spectrum generally assume that the accretion disk can be
characterized by material in a single ionization state. However, several
authors have recently stressed the importance of the classic ionization
instability for X-ray irradiated gas in hydrostatic balance. This instability
leads to a discontinuous transition in the vertical structure of the disk,
resulting in a hot ionized skin above much cooler material. If the Compton
temperature of the skin is high then even iron is completely ionized, and the
skin does not produce any spectral features. These new models, where the
ionization structure of the disk is calculated self-consistently, require an
excessive amount of computing power and so are difficult to use in directly
fitting observed X-ray spectra. Instead, we invert the problem by simulating
X-ray spectra produced by the new reflection models, and then fit these with
the old, single zone reflection models, to assess the extent to which the
derived accretion geometry depends on the reflection model used. We find that
the single zone ionization models can severely underestimate the covering
fraction of the ``cold'' material as seen from the X-ray source if the optical
depth in the ionized skin is of order unity, and that this can produce an
apparent correlation between the covering fraction and the X-ray spectral index
similar in nature to that reported by Zdziarski, Lubinski and Smith (1999).


title:
Spectroscopy of the candidate luminous blue variable at the center of
  the ring nebula G79.29+0.46

abstract:
  We report optical and near-infrared spectra of the central star of the radio
source G79.29+0.46, a candidate luminous blue variable. The spectra contain
numerous narrow (FWHM < 100 km/s emission lines of which the low-lying hydrogen
lines are the strongest, and resemble spectra of other LBVc's and B[e]
supergiants. A few prominent infrared lines are unidentified. The terminal wind
speed is determined from H alpha to be 110 km/s. The strength of H alpha
implies the presence of a very dense wind. Extended emission from H alpha and
[N II] was detected but appears to be associated with the Cygnus X region
rather than the radio source. Both diffuse interstellar bands and interstellar
absorption lines are present in the optical spectrum of the central star,
suggesting that there are both diffuse and molecular cloud components to the
extinction and implying a minimum distance of 1 kpc and minimum luminosity of
\~10^5 L(sun) for the star. The new spectra and their analysis indicate a low
excitation, dense, and slowly expanding wind and support the LBVc
classification.


title:
On the Association of Gamma-ray Bursts with Massive Stars: Implications
  for Number Counts and Lensing Statistics

abstract:
  Recent evidence appears to link gamma-ray bursts (GRBs) to star-forming
regions in galaxies at cosmological distances. If short-lived massive stars are
the progenitors of GRBs, the rate of events per unit cosmological volume should
be an unbiased tracer (i.e. unaffected by dust obscuration and surface
brightness limits) of the cosmic history of star formation. Here we use
realistic estimates for the evolution of the stellar birthrate in galaxies to
model the number counts, redshift distribution, and time-delay factors of GRBs.
We present luminosity function fits to the BATSE log N-log P relation for
different redshift distributions of the bursts. Our results imply about 1-2
GRBs every one million Type II supernovae, and a characteristic
`isotropic-equivalent' burst luminosity in the range 3-20 x 1e51 ergs/s (for
H_0=65 km/s/Mpc). We compute the rate of multiple imaging of background GRBs
due to foreground mass condensations in a Lambda-dominated cold dark matter
cosmology, assuming that dark halos approximate singular isothermal spheres on
galaxy scales and Navarro-Frenk-White profiles on group/cluster scales, and are
distributed in mass according to the Press-Schechter model. We show that the
expected sensivity increase of Swift relative to BATSE could result in a few
strongly lensed individual bursts detected down to a photon flux of 0.1
phot/s/cm^2 in a 3-year survey. Because of the partial sky coverage, however,
it is unlikely that the Swift satellite will observe recurrent events (lensed
pairs).


title:
RXTE observations of Seyfert-2 galaxies: evidence for spectral
  variability

abstract:
  We present a series of RXTE observations of the nearby obscured Seyfert
galaxies ESO103-G35, IC5063, NGC4507 and NGC7172. The period of monitoring
ranges from seven days for NGC7172 up to about seven months for ESO103-G035.
The spectra of all galaxies are well fit with a highly obscured (N_H>10^23
cm-2) power-law and an Fe line at 6.4 keV. We find strong evidence for the
presence of a reflection component in ESO103-G35 and NGC4507. The observed flux
presents strong variability on day timescales in all objects. Spectral
variability is also detected in the sense that the spectrum steepens with
increasing flux similar to the behaviour witnessed in some Seyfert-1 galaxies.


title:
Imaging the Universe in 3D with the VLT: The Next Generation Field
  Spectrometer SPIFFI

abstract:
  We present SPIFFI, the integral field spectrometer for the VLT. This
instrument allows simultaneous observation of infrared spectra in more than
1000 image points of a two dimensional field. With its set of four gratings and
a pixel scale that can be varied by a factor of ten, SPIFFI provides high
flexibility, and at the same time offers the unique possibility of diffraction
limited imaging spectroscopy at an 8m-class telescope, when fed by the adaptive
optics system MACAO. We outline the scientific drivers for building such an
instrument, the concept of image slicing, the optical design, and the
implementation of SPIFFI.


title: Electromagnetic radiation from superconducting string cusps

abstract:
  Cusps in superconducting cosmic strings produce strongly beamed
electromagnetic radiation. To calculate the energy emitted requires taking into
account the effect of the charge carriers on the string motion, which has
previously been done only heuristically. Here, we use the known exact solution
to the equations of motion for the case where the current is chiral to update
previous calculations for the total energy, spectrum and angular distribution
in that case. We analyze the dependence of the radiated energy on the cusp
parameters, and discuss which types of cusp dominate the total radiation
emitted from an ensemble.


title: Study of ammonia emission in the NGC 6334 region

abstract:
  The region centered in the NGC 6334 I(N) radio continuum source was surveyed
in an extension of 6 arcmin in right ascension and 12 arcmin in declination, in
the NH3(J,K) = (1,1) transition, using the Itapetinga radio telescope. The
spectra show non-LTE behavior, and gradients of velocity and line-width were
detected along the region. A detailed analysis of the spectra showed that the
surveyed region is composed of at least three overlapped sources related to
regions that are in different stages of star formation: NGC 6334 I, associated
with an already known molecular bipolar outflow, NGC 6334 I(N)w, the brightest
ammonia source, coincidental with the continuum source NGC 6334 I(N), and NGC
6334 I(N)e, weaker, more extended and probably less evolved than the others.
The physical parameters of the last two sources were calculated in non-LTE
conditions, assuming that their spectra are the superposition of the narrow
line spectra produced by small dense clumps. The H2 density, NH3 column
density, kinetic temperature, diameter and mass of the clumps were found to be
very similar in the two regions, but the density of clumps is lower in the
probably less evolved source NGC 6334 I(N)e. Differences between the physical
parameters derived assuming LTE and non-LTE conditions are also discussed in
this work.


title: Absolute dimensions of the unevolved B-type eclipsing binary GG Orionis

abstract:
  We present photometric observations in B and V as well as spectroscopic
observations of the detached, eccentric 6.6-day double-lined eclipsing binary
GG Ori, a member of the Orion OB1 association. Absolute dimensions of the
components, which are virtually identical, are determined to high accuracy
(better than 1% in the masses and better than 2% in the radii) for the purpose
of testing various aspects of theoretical modeling. We obtain M(A) = 2.342 +/-
0.016 solar masses and R(A) = 1.852 +/- 0.025 solar radii for the primary, and
M(B) = 2.338 +/- 0.017 solar masses and R(B) = 1.830 +/- 0.025 solar radii for
the secondary. The effective temperature of both stars is 9950 +/- 200 K,
corresponding to a spectral type of B9.5. GG Ori is very close to the ZAMS, and
comparison with current stellar evolution models gives ages of 65-82 Myr or 7.7
Myr depending on whether the system is considered to be burning hydrogen on the
main sequence or still in the final stages of pre-main sequence contraction. We
have detected apsidal motion in the binary at a rate of dw/dt = 0.00061 +/-
0.00025 degrees per cycle, corresponding to an apsidal period of U = 10700 +/-
4500 yr. A substantial fraction of this (approximately 70%) is due to the
contribution from General Relativity.


title: Does Pulsar B1757--24 Have a Fallback Disk?

abstract:
  Radio pulsars are thought to spin-down primarily due to torque from magnetic
dipole radiation (MDR) emitted by the time-varying stellar magnetic field as
the star rotates. This assumption yields a `characteristic age' for a pulsar
which has generally been assumed to be comparable to the actual age. Recent
observational limits on the proper motion of pulsar B1757-24, however, revealed
that the actual age (>39 kyr) of this pulsar is much greater than its MDR
characteristic age (16 kyr) - calling into question the assumption of pure MDR
spin-down for this and other pulsars. To explore the possible cause of this
discrepancy, we consider a scenario in which the pulsar acquired an accretion
disk from supernova ejecta, and the subsequent spin-down occurred under the
combined action of MDR and accretion torques. A simplified model of the
accretion torque involving a constant mass inflow rate at the pulsar
magnetosphere can explain the age and period derivative of the pulsar for
reasonable values of the pulsar magnetic field and inflow rate. We discuss
testable predictions of this model.


title: Optical Variability of the T Tauri Star HH30

abstract:
  We report results of VRI photometric monitoring of the T Tauri star plus disk
system HH30. We find that HH30 is highly variable over timescales of a few days
with Delta V~1.5 mag, Delta I~1.1 mag. Furthermore we find hints of periodicity
with periodograms indicating possible periods of 11.6 and 19.8 days. The VRI
photometry is available through the anonymous ftp service. We model the
variability with Monte Carlo radiation transfer simulations for a spotted star
plus disk system and find that the large variability is best reproduced with a
single hot spot and circumstellar grains that are larger than typical
interstellar grains. The apparent existence of a single hot spot and the need
for larger, more forward throwing grains is consistent with previous modeling
of HST imagery.


title: A New Look at Simple Inhomogeneous Chemical Evolution

abstract:
  A rudimentary, one-zone, closed-box model for inhomogeneous chemical
evolution is offered as an alternative reference than the Simple model in the
limit of no mixing. The metallicity distribution functions (MDFs) of Galactic
halo and bulge stars can be matched by varying a single evolutionary parameter,
nQ. Q is the filling factor of contaminating regions and n is the number of
star-forming generations. Therefore, Q and n have equivalent roles, and
combinations of n and Q yield systems with different metallicities at any given
age. The model also revises interpretation of observed MDFs. Unevolved systems
probe the parent distribution of metal production f(z), for example, the
high-metallicity tail of the halo distribution agrees with a power-law f(z).


title:
Recent X-ray Observations of Disk Galaxies: Tracing the Dynamic
  Interstellar Medium

abstract:
  I review recent results from our deep ROSAT and Chandra observations of two
galaxies, M101 and NGC 4631, in fields of exceptionally low Galactic
extinction. Large amounts of X-ray-emitting gas are detected in these galaxies.
Such gas is produced primarily in massive star forming regions and have an
average characteristic temperature of a few times $10^6$ K. Cooler gas ($\sim
10^6$ K) is found typically outside galactic disks and may represent outflows
from blown-out superbubbles. Propagation of star formation, driven by the
expansion of hot gas, appears to be operating in giant HII complexes. A
substantial fraction of photo-evaporated gas in such complexes may be
mass-loaded into hot gas, which explains their large X-ray luminosities. These
processes likely play an important role in determining the global properties of
the interstellar medium, especially the disk/halo interaction.


title:
Effects of Environment and Energy Injection on Gamma-Ray Burst
  Afterglows

abstract:
  There is growing evidence that some long gamma-ray bursts (GRBs) arise from
the core collapse of massive stars, and thus it is inevitable that the
environments of these GRBs are preburst stellar winds or dense media. We
studied, for the first time, the wind model for afterglows based on the
Blandford-McKee self-similar solution of a relativistic shock, and suggested
that GRB 970616 is an interactor with a stellar wind. We also proposed a dense
medium model for some afterglows, e.g., the steepening in the light curve of
the R-band afterglow of GRB 990123 may be caused by the adiabatic shock which
has evolved from an ultrarelativistic phase to a nonrelativistic phase in a
dense medium. We further discussed the dense medium model in more details, and
investigated the effects of synchrotron self absorption and energy injection. A
shock in a dense medium becomes nonrelativistic rapidly after a short
relativistic phase. The afterglow from the shock at the nonrelativistic stage
decays more rapidly than at the relativistic stage. Since some models for GRB
energy sources predicted that a strongly magnetic millisecond pulsar may be
born during GRB formation, we discussed the effect of such a pulsar on the
evolution of the nonrelativistic shock through magnetic dipole radiation. We
found that in the pulsar energy injection case, the dense medium model fits
very well all the observational data of GRB 980519. Recently, we combined the
dense medium model with the pulsar energy injection effect to provide a good
fit to the optical afterglow data of GRB 000301C.


title: Biased Galaxy Formation And Measurements Of Beta

abstract:
  Measurements of the cosmological density parameter Omega using techniques
that exploit the gravity-induced motions of galaxies constrain, in linear
perturbation theory, the degenerate parameter combination beta = Omega^{0.6}/b,
where the linear bias parameter b is the ratio of the fluctuation amplitudes of
the galaxy and mass distributions. However, the relation between the galaxy and
mass density fields depends on the complex physics of galaxy formation, and it
can in general be non-linear, stochastic, and perhaps non-local. The
one-parameter linear bias model is almost certainly oversimplified, which leads
to the obvious question: What is the quantity beta that is actually measured by
different techniques? To address this question, we estimate beta from galaxy
distributions that are constructed by applying a variety of locally biased
galaxy formation models to cosmological N-body simulations. We compare the
values of beta estimated using three different techniques: a density-density
comparison similar to the POTENT analysis, a velocity-velocity comparison
similar to the VELMOD analysis, and an anisotropy analysis of the
redshift-space power spectrum. In most cases, we find that beta estimated using
all three methods is similar to the asymptotic value of
Omega^{0.6}/b_{sigma}(R) at large R, where b_{sigma}(R) is the ratio of rms
galaxy fluctuations to rms mass fluctuations on scale R. Thus, something close
to the conventional interpretation of beta continues to hold even for complex
bias models. Moreover, we find that beta estimates made using these three
methods should, in principle, agree with each other. It is thus unlikely that
non-linear or scale-dependent bias is responsible for the discrepancies that
exist among current measurements of beta from different techniques.


title:
Can luminosity distance measurements probe the equation of state of dark
  energy

abstract:
  Distance measurements to Type Ia supernovae (SNe Ia) at cosmological
distances indicate that the Universe is accelerating and that a large fraction
of the critical energy density exists in a component with negative pressure.
Various hypotheses on the nature of this ``dark energy'' can be tested via
their prediction for the equation of state of this component. If the dark
energy is due to a scalar field, its equation of state will in general vary
with time and is related to the potential of the field. We review the intrinsic
degeneracies of luminosity distance measurements and compute the expected
accuracies that can be obtained for the equation of state parameter from a
realistic high statistic SNe Ia experiment.


title:
Science User Scenarios for a Virtual Observatory Design Reference
  Mission: Science Requirements for Data Mining

abstract:
  The knowledge discovery potential of the new large astronomical databases is
vast. When these are used in conjunction with the rich legacy data archives,
the opportunities for scientific discovery multiply rapidly. A Virtual
Observatory (VO) framework will enable transparent and efficient access,
search, retrieval, and visualization of data across multiple data repositories,
which are generally heterogeneous and distributed. Aspects of data mining that
apply to a variety of science user scenarios with a VO are reviewed. The
development of a VO should address the data mining needs of various
astronomical research constituencies. By way of example, two user scenarios are
presented which invoke applications and linkages of data across the catalog and
image domains in order to address specific astrophysics research problems.
These illustrate a subset of the desired capabilities and power of the VO, and
as such they represent potential components of a VO Design Reference Mission.


title:
Structure and evolution of the inner Milky Way galaxy: results from
  ISOGAL

abstract:
  The DENIS/ISOGAL near/mid-IR survey of the Milky Way for the first time
probes stellar populations in the innermost obscured regions of our galaxy.
Ages, metallicities and extinction-corrected luminosities are derived for these
stars individually. An old metal-rich population dominates in the inner
galactic Bulge, but there are also indications for the presence of a younger
population. The inner Bulge has a tri-axial shape, as traced by depth effects
on the observed luminosity distributions.


title:
Possible direct method to determine the radius of a star from the
  spectrum of gravitational wave signals

abstract:
  We computed the spectrum of gravitational waves from a dust disk star of
radius R inspiraling into a Kerr black hole of mass M and specific angular
momentum a. We found that when R is much larger than the wave length of the
quasinormal mode, the spectrum has several peaks and the separation of peaks
$\Delta\omega$ is proportional to $R^{-1}$ irrespective of M and a. This
suggests that the radius of the star in coalescing binary black hole - star
systems may be determined directly from the observed spectrum of gravitational
wave. This also suggests that the spectrum of the radiation may give us
important information in gravitational wave astronomy as in optical astronomy.


title: The M(BH)-Sigma Relation for Supermassive Black Holes

abstract:
  We investigate the differences in the M(BH)-sigma relation derived recently
by Ferrarese & Merritt (2000) and Gebhardt et al. (2000). The shallower slope
found by the latter authors (3.75 vs. 4.8) is due partly to the use of a
regression algorithm that ignores measurement errors, and partly to the value
of the velocity dispersion adopted for a single galaxy, the Milky Way. A
steeper relation is shown to provide a better fit to black hole masses derived
from reverberation mapping studies. Combining the stellar dynamical, gas
dynamical, and reverberation mapping mass estimates, we derive a best-fit
relation M(BH) = 1.30 (+/- 0.36) X 10^8 (sigma_c/200)^{4.72(+/- 0.36)}, where
M(BH) is in solar masses, and sigma in km/s.


title: A Submillimeter Study of the Star-Forming Region NGC7129

abstract:
  New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps
of the NGC7129 star forming region are presented, complemented by C18O J=3-2
spectra at several positions within the mapped region. The maps include the
Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and
several other pre-stellar sources embedded within the molecular ridge.
  The SCUBA maps help us understand the nature of the pre-main sequence stars
in this actively star forming region. A deeply embedded submillimeter source,
SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar
core or possibly a protostar. The highest continuum peak emission is identified
with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234,
and also responsible for both the optical jet and the molecular outflow. The
gas and dust masses are found to be consistent, suggesting little or no CO
depletion onto grains. The dust emissivity index is lower towards the dense
compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding
cloud, implying small size grains in the PDR ridge, whose mantles have been
evaporated by the intense UV radiation.


title: Photometric Properties of the Arp 220 Super Star Clusters

abstract:
  We investigate the photometric properties of six super stellar clusters
(SSCs) seen in both the optical and near-infrared Hubble Space Telescope images
of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs are
located in the central 0.5 kpc region. The remaining three are in the
circumnuclear region between 0.5 kpc and 2.5 kpc from the centre. Comparing the
observed spectral energy distributions (SEDs) of the SSCs with the Starburst99
models of Leitherer et al., we confirm that all the three nuclear SSCs are
heavily obscured ($A_V \sim 10$ mag). Considering the results from this
comparison in conjunction with measurements of the near-infrared CO absorption
index and of millimetre CO line widths and luminosities, we estimate the ages
of the nuclear SSCs to be $10^7 - 10^8$ yrs. The bolometric luminosity of the
three nuclear SSCs is at most one-fifth of the total bolometric luminosity of
Arp 220. On the other hand, the circumnuclear SSCs have little internal
extinction ($A_V \leq$ 1 mag). These contribute negligibly to the total
bolometric luminosity.


title: Distribution of dust and stars in the Galaxy

abstract:
  Using far-infrared 240 micron and near-infrared K band data from the
COBE/DIRBE instrument, we model the Galactic stellar and dust distribution.
Making the assumption that the Galaxy is transparent in the 240 micron band,
the dust emission is modeled using the following components: a warped
exponential disk of scale length 0.26 R_sun, a spiral arm component as mapped
by HII regions, and a feature coinciding with the local (Orion) arm. The dust
distribution is used to calculate absorption in the K band, and the stellar
emission is likewise modeled with a warped exponential disk, with a scale
length of 0.29 R_sun, and a spiral arm component. Models of the K band emission
in the Galactic plane indicate that in this waveband a two arm spiral dominates
the nonaxisymmetric emission. The warp is evident in both the dust and stellar
component, and is found to start within the Solar Circle.


title: Opportunities for future supernova studies of cosmic acceleration

abstract:
  We investigate the potential of a future supernova dataset, as might be
obtained by the proposed SNAP satellite, to discriminate among different ``dark
energy'' theories that describe an accelerating Universe. We find that many
such models can be distinguished with a fit to the effective
pressure-to-density ratio, $w$, of this energy. More models can be
distinguished when the effective slope, $dw/dz$, of a changing $w$ is also fit,
but only if our knowledge of the current mass density, $\Omega_m$, is improved.
We investigate the use of ``fitting functions'' to interpret luminosity
distance data from supernova searches, and argue in favor of a particular
preferred method, which we use in our analysis.


title: An HST Lensing Survey of X-ray Luminous Galaxy Clusters: I. A383

abstract:
  We analyse the mass distribution in the core of A383 (z=0.188), one of 12
X-ray luminous clusters at z~0.2 selected for a comprehensive and unbiased
study of the mass distribution in massive clusters. Deep HST imaging reveals a
wide variety of gravitationally lensed features in A383, including a giant arc
formed from the strongly-lensed images of 2 background galaxies, 2 radial arcs,
several multiply-imaged arcs and numerous arclets. Based upon the constraints
from the various lensed features, we construct a detailed mass model for the
central regions of the cluster, taking into account both the cluster-scale
potential and perturbations from individual cluster galaxies. Keck spectroscopy
of one component of the giant arc identifies it as a star-forming galaxy at
z=1.01 and provides an accurate measurement of the cluster mass within the
radius of the giant arc (65kpc) of (3.5+/-0.1)*10^13 Mo. Using the weak shear
measured from our HST observations we extend our mass model to determine a mass
of (1.8+/-0.2)*10^14 Mo within a radius of 250kpc. On smaller scales we employ
the radial arcs as probes of the shape of the mass distribution in the cluster
core (r<20kpc), and find that the mass profile is more peaked than a single NFW
profile. The optical and X-ray properties of A383 indicate the presence of a
central cooling flow, for which we derive a mass deposition rate of >200 Mo/yr.
We also use the X-ray emission from A383 to obtain independent estimates of the
total mass within projected radii of 65 and 250kpc: (4.0+/-1.4)*10^13 Mo and
(1.2+/-0.5)*10^14 Mo, which are consistent with the lensing measurements.
[Abridged]


title:
ISO-SWS calibration and the accurate modelling of cool-star atmospheres:
  I. Method

abstract:
  A detailed spectroscopic study of the ISO-SWS data of the red giant Alpha Tau
is presented, which enables not only the accurate determination of the stellar
parameters of Alpha Tau, but also serves as a critical review of the ISO-SWS
calibration.
  This study is situated in a broader context of an iterative process in which
both accurate observations of stellar templates and cool star atmosphere models
are involved to improve the ISO-SWS calibration process as well as the
theoretical modelling of stellar atmospheres. Therefore a sample of cool stars,
covering the whole A0 -- M8 spectral classification, has been observed in order
to disentangle calibration problems and problems in generating the theoretical
models and corresponding synthetic spectrum.
  By using stellar parameters found in the literature large discrepancies were
seen between the ISO-SWS data and the generated synthetic spectrum of Alpha
Tau. A study of the influence of various stellar parameters on the theoretical
models and synthetic spectra, in conjunction with the Kolmogorov-Smirnov test
to evaluate objectively the goodness-of-fit, enables us to pin down the stellar
parameters with a high accuracy: Teff = 3850 +/- 70 K, log g = 1.50 +/- 0.15, M
= 2.3 +/- 0.8 Msun, z = -0.15 +/- 0.20 dex, microturbulence = 1.7 +/- 0.3 km/s,
12C/13C= 10 +/- 1, abundance of C = 8.35 +/- 0.20 dex, abundance of N= 8.35 +/-
0.25 dex, abundance of O = 8.83 +/- 0.15 dex and the angular diameter is 20.77
+/- 0.83 mas. These atmospheric parameters were then compared with the results
provided by other authors using other methods and/or spectra.


title: NGC1614: A Laboratory for Starburst Evolution

abstract:
  The modest extinction and reasonably face-on viewing geometry make the
luminous IR galaxy NGC1614 an ideal laboratory for study of a powerful
starburst. HST/NICMOS observations show: 1.) deep CO stellar absorption,
tracing a starburst nucleus about 45 pc in diameter; 2.) surrounded by a ~600
pc diameter ring of supergiant HII regions revealed in Pa$\alpha$ line
emission; 3.) lying within a molecular ring indicated by its extinction shadow
in H-K; 4.) all at the center of a disturbed spiral galaxy. The luminosities of
the giant HII regions in the ring are extremely high, an order of magnitude
brighter than 30 Doradus. The relation of deep stellar CO bands to surrounding
ionized gas ring to molecular gas indicates that the luminous starburst started
in the nucleus and is propagating outward into the surrounding molecular ring.
This hypothesis is supported by evolutionary starburst modeling that shows that
the properties of NGC1614 can be fitted with two short-lived bursts of star
formation separated by 5 Myr. The total dynamical mass of the starburst region
of 1.3x10^9 Msol is mostly accounted for by the old pre-star burst stellar
population. Although our starburst models use a modified Salpeter IMF, the
tight mass budget suggests that the IMF may contain relatively more 10-30 Msol
stars and fewer low mass stars than the Salpeter function. The dynamical mass
is nearly 4 times smaller than the mass of molecular gas estimated from the
standard ratio of 12CO(1-0) to H2. A number of arguments place the mass of gas
in the starburst region at ~25% of the dynamical mass, nominally about 1/15 and
with an upper limit of 1/10 of the amount estimated from 12CO and the standard
ratio. (Abridged)


title: The WIMP annual modulation signal and non-standard halo models

abstract:
  Currently the best prospect for detecting Weakly Interacting Massive
Particles (WIMPs) is via the annual modulation, which occurs due to the Earth's
rotation around the Sun, of the direct detection signal. We investigate the
effect of uncertainties in our knowledge of the structure of the galactic halo
on the WIMP annual modulation signal. We compare the signal for three
non-standard halo models: Evans' power-law halos, Michie models with an
asymmetric velocity distribution and Maxwellian halos with bulk rotation. We
then compare the theoretical predictions of these models with the experimental
signal found by the DAMA experiment and investigate how the WIMP mass and
interaction cross section determined depend on the halo model assumed. We find
that the WIMP mass confidence limits are significantly extended to larger
masses, with the shape of the allowed region in the mass-cross section plane
depending on the model.


title: Bimodal Accretion Disks: SSD-ADAF Transitions

abstract:
  We show that, unlike the results presented previously in the literature, the
transition from an outer Shakura-Sunyaev disk (SSD) to an advection-dominated
accretion flow (ADAF) is possible for large values of the viscosity parameter
$\alpha >0.5$. The transition is triggered by thermal instability of a
radiation-pressure-supported SSD. The transition radius is close to the central
black hole. We confirm our qualitative prediction by actually constructing
global bimodal SSD-ADAF solutions.


title: Comparing Giant Molecular Clouds in M31, M33 & the Milky Way

abstract:
  We present new observations of a 2' field in the north-eastern spiral arm of
M31. In the 0.8 x 3.6 kpc mosaicked region, we have detected six distinct,
large complexes of molecular gas, most of which lie along the spiral arm dust
lane or in the vicinity of HII regions. The mean properties of these complexes
are as follows: diameter ~ 57+/-13 pc, fwhm velocity ~ 6.5+/-1.2 km/s, M(CO) ~
3.0+/-1.6 x 10^5 solar masses, peak brightness temperatures ~ 1.6--4.2 K. We
investigate the effects of spatial filtering on the quantitative comparison of
Local Group and Milky Way giant molecular clouds properties and distributions.
We also discuss different cloud identification techniques and their impact on
derived cloud properties. When we employ the same cloud identification method
and account for differences in data acquisition for M31, Milky Way, and M33, we
find that the molecular cloud complexes in all three galaxies are similar.
While the global distribution of molecular gas may vary from galaxy to galaxy,
cloud complexes are similar, suggesting that cloud formation and destruction is
determined by local physics. This work is supported by grants AST-9613716 &
AST-9981289 from the National Science Foundation.


title: 85-GHz BIMA observations of the double-hotspot radio galaxy 3C20

abstract:
  We present 85-GHz observations of the archetypal double-hotspot radio source
3C20 made with the BIMA millimetre array. The resolution of BIMA allows us to
separate the two components of the eastern hotspot. By comparing the BIMA
observations with existing VLA data, we show that the spectra of the two
hotspot components are very similar, despite the clear differences in their
radio structure and their wide separation. We discuss the implications for
models of double hotspot formation. Weak emission from the lobes of 3C20 is
detected at 85 GHz, at a level consistent with the predictions of standard
spectral ageing models.


title: The SPIFFI image slicer: Revival of image slicing with plane mirrors

abstract:
  SPIFFI (SPectrometer for Infrared Faint Field Imaging) is the integral field
spectrograph of the VLT-instrument SINFONI (SINgle Far Object Near-infrared
Investigation). SINFONI is the combination of SPIFFI with the ESO adaptive
optics system MACAO (Multiple Application Concept for Adaptive Optics) offering
for the first time adaptive optics assisted near infrared integral field
spectroscopy at an 8m-telescope. SPIFFI works in the wavelength ranger from 1.1
to 2.5 micron with a spectral resolving power ranging from R=2000 to 4500.
Pixel scale ranges from 0.25 to 0.025 seconds of arc. The SPIFFI field-of-view
consists of 32x32 pixels which are rearranged with an image slicer to a form a
long slit. Based on the 3D slicer concept with plane mirrors, an enhanced image
slicer was developed. The SPIFFI image slicer consists of two sets of mirrors,
called the 'small' and the 'large' slicer. The small slicer cuts a square field
of view into 32 slitlets, each of which is 32 pixels long. The large slicer
rearranges the 32 slitlets into a 1024 pixels long slit. The modifications to
the 3D slicer concept affect the angles of the plane mirrors of small and large
slicer and lead to an improved slit geometry with very little light losses. At
a mirror width of 0.3mm the light loss is <5%. All reflective surfaces are flat
and can be manufactured with a high surface quality. This is especially
important for the adaptive optics mode of SINFONI. We explain the concept of
the SPIFFI mirror slicer and describe details of the manufacturing process.


title: A Newly Discovered SU UMa-Type Dwarf Nova, HS 1449+6415

abstract:
  We report time-resolved photometric observations of the Hamburg Quasar
Survey-selected dwarf nova HS 1449+6415 (= RX J1450.5+6403) during the interval
from JD 2451672 to 2451724. During a long outburst with a duration of ~12 days,
we detected superhumps with a period of 0.0601(5) d, revealing that this star
is an SU UMa star. A short outburst which lasted 3 days was found about 40 days
after the onset of the superoutburst. From quiescence observations, we
determine an orbital period of 0.05898(2) d. The small outburst amplitude of
\~3.5 mag, the short orbital period, and the normal outburst cycle length
suggest that HS 1449+6415 is an intermediate object between ER UMa stars with
high mass-transfer rates and WZ Sge stars with very low mass-transfer rates.


title: HST Optical-NIR Colors of Nearby $R^{1/4}$ and Exponential Bulges

abstract:
  We have analysed $V$, $H$ and $J$ HST images for a sample of early- to
late-type spiral galaxies, and reported elsewhere the statistical frequency of
$R^{1/4}$-law and exponential bulges in our sample as a function of Hubble
type, and the frequency of occurrence and structural properties of the resolved
central nuclei hosted by intermediate- to late-type bulges and disks (see
references in the text). Here we use these data to show that: {\it (i)} The
$V-H$ color distribution of the $R^{1/4}$ bulges peaks around $<V-H> \sim 1.3$,
with a sigma $\Delta (V-H) \sim 0.1$ magnitudes. Assuming a solar metallicity,
these values correspond to stellar ages of $\approx 6 \pm 3$ Gyrs. In contrast,
the $V-H$ color distribution of the exponential bulges peaks at $<V-H> \sim
0.9$ and has a sigma $\Delta (V-H) \sim 0.4$ mags. This likely implies
significantly smaller ages and/or lower metallicities for (a significant
fraction of the stars in) the exponential bulges compared to the $R^{1/4}$-law
spheroids. {\it (ii)} Most of the central nuclei hosted by the exponential
bulges have $V-H$ and $J-H$ colors which are compatible with relatively
unobscured stellar populations. Assuming no or little dust effects, ages $\gta
1$ Gyrs are suggested for these nuclei, which in turn imply masses of about a
few 10$^6$ to a few 10$^7$ M$_\odot$, i.e., sufficient to dissolve progenitor
bars with masses consistent with those inferred for the exponential bulges by
their luminosities. {\it (iii)} While different bulge-nucleus pairs cover a
large range of $V-H$ colors, each bulge-nucleus pair has quite similar $V-H$
colors, and thus possibly similar stellar populations. (abridged)


title:
Response of circumnuclear water masers to luminosity changes in an
  active galactic nucleus

abstract:
  Circumnuclear water masers can respond in two ways to changes in the
luminosity of an active galactic nucleus. First, an increase in the X-ray
luminosity can lead to an increase in the maser emissivity; and second, an
increase in the intrinsic bolometric luminosity may result in a temporary
decrease in the difference between the gas and dust temperature and a
consequent decrease in the maser output. Whilst the latter effect can occur
over a period shorter than the thermal timescale, the former effect cannot.
Quantitative estimates of the response of the water maser emissivity to changes
in either the X-ray or bolometric luminosity are presented, together with
estimates of the relevant timescales. Either mechanism could account for recent
observations by Gallimore et al. which suggest that the water maser variability
in two widely separated regions of the circumnuclear gas in NGC 1068 have been
coordinated by a signal from the active nucleus. For either mechanism, a
minimum H2 density ~ 1.E+8 cm-3 is needed to explain the observed variability
timescale.


title: New VLBI Constraints for 0957+561 Lens Models

abstract:
  Time-delay measurements of 0957+561 based on radio monitoring now agree with
optical monitoring. Recent models incorporate many recent observations, but the
systematic uncertainties in the models still dominate the uncertainty in the
cosmological results. VLBI observations of the milli-arcsec jet structure have
provided the most important set of modeling constraints. We present new
observations of this structure, made at 18 cm with the Very Long Baseline
Array, the Very Large Array, and the Green Bank 140 ft. telescope. Compared to
the data set of Garrett et al. (1994), ours has a similar theoretical noise
level (20 microJy), but nearly twice as many baselines (66 compared to 36) and
more uniform coverage of the UV plane. Our initial maps confirm the basic jet
structures seen by Garrett et al., with comparable RMS noise (60-80 microJy),
and are in reasonable agreement with the jet structure model of Barkana et al.
(1999). The maps also hint at a new compact component leaving the core, and a
previously undetected diffuse component at the end of the jet. Further
refinements in fringe-fitting, mapping, and self-calibration should yield
significantly lower RMS noise (closer to the theoretical level). We will use a
modified form of the CalTech VLBI Modelfit program (written by Barkana et al.
1999) to determine the magnification matrix between the images. The refined
magnification matrix should provide stronger constraints on the lens model, and
thus reduce the uncertainty in the cosmological results.


title: What is the behavior of the ISM in the SMC?

abstract:
  We describe quantitatively the neutral hydrogen (HI) and dust content of the
interstellar medium (ISM) in the Small Magellanic Cloud (SMC), using the
spatial power spectrum. The velocity modification of the HI density power
spectrum is investigated and discussed.


title:
A Deep Multicolor Survey. VI. Near-Infrared Observations, Selection
  Effects, and Number Counts

abstract:
  I present near-infrared J (1.25um), H (1.65um), and K (2.2um) imaging
observations of 185 square arcminutes in 21 high galactic latitude fields.
These observations reach limiting magnitudes of J ~ 21 mag, H ~ 20 mag and K ~
18.5 mag. The detection efficiency, photometric accuracy and selection biases
as a function of integrated object brightness, size, and profile shape are
quantified in detail. I evaluate several popular methods for measuring the
integrated light of faint galaxies and show that only aperture magnitudes
provide an unbiased measure of the integrated light that is independent of
apparent magnitude. These J, H, and K counts and near-infrared colors are in
best agreement with passive galaxy formation models with at most a small amount
of merging (for Omega_M = 0.3, Omega_Lambda = 0.7).


title: Why is the Fraction of Four-Image Radio Lens Systems So High?

abstract:
  We investigate the frequency of two- and four-image gravitational lens
systems in the Jodrell-VLA Astrometric Survey (JVAS) and Cosmic Lens All-Sky
Survey (CLASS), and the possible implications for dark matter halo properties.
A simple lensing statistics model, which describes lens galaxies as singular
isothermal ellipsoids with a projected axis ratio distribution derived from the
surface brightness ellipticities of early-type galaxies in the Coma cluster, is
ruled out at the 98% level since it predicts too few four-image lenses (quads).
We consider a range of factors that may be increasing the frequency of radio
quads, including external shear fields, mass distributions flatter than the
light, shallow lensing mass profiles, finite core radii, satellite galaxies,
and alterations to the luminosity function for faint flat-spectrum radio
sources. We find that none of these mechanisms provide a compelling solution to
the quad problem on their own while remaining consistent with other
observational constraints.


title: A Test for the Nature of the Type Ia Supernova Explosion Mechanism

abstract:
  Currently popular models for Type Ia supernovae (SNe Ia) fall into two
general classes. The first comprises explosions of nearly pure carbon/oxygen
(C/O) white dwarfs at the Chandrasekhar limit which ignite near their centers.
The second consists of lower-mass C/O cores which are ignited by the detonation
of an accreted surface helium layer. Explosions of the latter type produce
copious Fe, Co and Ni K-alpha emission from 56Ni and 56Co decay in the
detonated surface layers, emission which is much weaker from Chandrasekhar-mass
models. The presence of this emission provides a simple and unambiguous
discriminant between these two models for SNe Ia. Both mechanisms may produce
0.1-0.6 solar masses of 56Ni, making them bright gamma-ray line emitters. The
time to maximum brightness of 56Ni decay lines is distinctly shorter in the
sub-Chandrasekhar mass class of model (approximately 15 days) than in the
Chandrasekhar mass model (approximately 30 days), making gamma-ray line
evolution another direct test of the explosion mechanism. It should just be
possible to detect K-shell emission from a sub-Chandrasekhar explosion from SNe
Ia as far away as the Virgo cluster with the XMM Observatory. A 1 to 2 square
meter X-ray telescope such as the proposed Con-X Observatory could observe
K-alpha emission from sub-Chandrasekhar mass SNe Ia in the Virgo cluster,
providing not just a detection, but high-accuracy flux and kinematic
information.


title:
Discovery of a Slow X-Ray Pulsator, AX J1740.1-2847, in the Galactic
  Center Region

abstract:
  We report the discovery of an X-ray pulsar AX J1740.1-2847 from the Galactic
center region. This source was found as a faint hard X-ray object on 7--8
  September 1998 with the ASCA Galactic center survey observation. Then,
coherent pulsations of P=729 +/- 14 sec period were detected. The
  X-ray spectrum is described by a flat power-law of ~= 0.7 photon index. The
large absorption column of log NH ~= 22.4
  (cm^-2) indicates that AX J1740.1-2847 is a distant source, larger than 2.4
kpc, and possibly near at the Galactic center region. The luminosity in the
2--10 keV band is larger than 2.5 x 10^33 erg/s, or likely to be 3.2 x 10^34
erg/s at the Galactic center distance. Although the slow pulse period does not
discriminate whether AX J1740.1-2847 is a white dwarf or neutron star binary,
the flat power-law and moderate luminosity strongly favor a neutron star
binary.


title:
Comparison of the Two Followup Observation Strategies for Gravitational
  Microlensing Planet Searches

abstract:
  There are two different strategies of followup observations for the detection
of planets by using microlensing. One is detecting the light curve anomalies
affected by the planetary caustic from continuous monitoring of all events
detected by microlensing survey programs (type I strategy) and the other is
detecting anomalies near the peak amplification affected by the central caustic
from intensive monitoring of high amplification events (type II strategy). It
was shown by Griest & Safizadeh that the type II strategy yields high planet
detection efficiency per event. However, it is not known the planet detection
rate by this strategy can make up a substantial fraction of the total rate. In
this paper, we estimate the relative planet detection rates expected under the
two followup observation strategies. From this estimation, we find that the
rate under the type II strategy is substantial and will comprise $\sim 1/4$ --
1/2 of the total rate. We also find that compared to the type I strategy the
type II strategy is more efficient in detecting planets located outside of the
lensing zone. We determine the optimal monitoring frequency of the type II
strategy to be $\sim 20$ times/night, which can be easily achieved by the
current microlensing followup programs even with a single telescope.


title:
Radio Halos of Galaxy Clusters from Hadronic Secondary Electron
  Injection in Realistic Magnetic Field Configurations

abstract:
  We investigate the possibility that radio halos of clusters of galaxies are
caused by synchrotron emission of cosmic ray electrons (CRe), which were
produced by cosmic ray protons (CRp) interacting hadronically with the
intra-cluster medium (ICM) protons. We perform cosmological
magneto-hydrodynamics (MHD) simulations to obtain a sample of ten magnetized
galaxy clusters. They provide realistic models of the gas and magnetic field
distribution, needed to predict the CRe production rates, their cooling, and
their synchrotron emissivity. We assume a CRp population within the ICM with an
energy density which has a constant ratio to thermal energy density. This ratio
is adjusted in such a way that one of the simulated clusters reproduces the
radio luminosity of the radio halo of the Coma cluster of galaxies. Our model
exhibits the observed low degree of radio polarization and has a similar radial
emission profile as the Coma cluster. We provide estimates for the expected
gamma ray and neutrino flux. The necessary CRp/thermal energy ratio is 4 ...
14% ${(E_{p,min}/GeV)}^{-0.375}$ (for the range of magnetic field strengths
suggested by Faraday measurements), where $E_{p,min}$ is the lower kinetic
energy cutoff of the CRp with spectral index $\alpha_p \approx 2.375$. Assuming
this ratio to be the same in the whole set of simulated clusters a $T_x-L_\nu$
relation is predicted which follows the observed relation well.


title:
Phenomenon of Gamma-Ray Bursts as Relativistic Detonation of Scalar
  Fields

abstract:
  In the modern Universe the existence of various forms of scalar fields is
supposed. On the one hand these fields can explain recently discovered positive
$\Lambda$-term(see e.g. Ref. \cite{ref:Sahni}), on the other hand its form
cluster systems creating gravitational wells for galaxies and their clusters.
At that a natural hypothesis is the existence of compact configurations
("stars") from scalar fields with a large enough energy density and total mass.
The hypothesis is that the energy of these fields can be converted in
relativistic plasma by an explosive way. Such process can be initiated by
collision of relativistic particles which form a relativistic microscopic
fireball. Thus effective temperature can amount to value sufficient for change
of phase for scalar fields. Then the wave of relativistic "detonation" similar
to the same process in classical physics will be spread from this source. In
this paper the parameters of such field star and process of detonation are
estimated. If the effect of the indicated change of phase (or something similar
to one) exists, it is possible to get the parameters of relativistic plasma
(macroscopic fireball) which could generate gamma - bursts. If in the modern
Universe there is such unique form of a matter as fields of high density it
would be strange for Nature not to take advantage of the possibility to convert
their energy to radiation by an explosive way.


title: Unidentified Infrared Emission Bands in the Diffuse Interstellar Medium

abstract:
  Using the Mid-Infrared Spectrometer on board the Infrared Telescope in Space
and the low-resolution grating spectrometer (PHT-S) on board the Infrared Space
Observatory, we obtained 820 mid-infrared (5 to 12 $\mu$m) spectra of the
diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina
Nebula regions. These spectra indicate that the emission is dominated by the
unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 $\mu$m.
The relative band intensities (6.2/7.7 $\mu$m, 8.6/7.7 $\mu$m, and 11.2/7.7
$\mu$m) were derived from these spectra, and no systematic variation in these
ratios was found in our observed regions, in spite of the fact that the
incident radiation intensity differs by a factor of 1500. Comparing our results
with the polycyclic aromatic hydrocarbons (PAHs) model for the UIR band
carriers, PAHs in the DIM have no systematic variation in their size
distribution, their degree of dehydrogenation is independent of the strength of
UV radiation field, and they are mostly ionized. The latter finding is
incompatible with past theoretical studies, in which a large fraction of
neutral PAHs is predicted in this kind of environment. A plausible resolution
of this discrepancy is that the recombination coefficients for electron and
large PAH positive ion are by at least an order of magnitude less than those
adopted in past theoretical studies. Because of the very low population of
neutral state molecules, photoelectric emission from interstellar PAHs is
probably not the dominant source of heating of the diffuse interstellar gas.
The present results imply constant physical and chemical properties of the
carriers of the UIR emission bands in the DIM.


title:
The impact of chemical evolution on the observable properties of stellar
  populations

abstract:
  The major effects of the chemical evolution of galaxies on the
characteristics of their stellar populations are reviewed. A few examples of
how the observed stellar properties derived from colour--magnitude diagrams can
constrain chemical evolution models are given.


title:
Cosmological Relativity: A General-Relativistic Theory for the
  Accelerating Expanding Universe

abstract:
  Recent observations of distant supernovae imply, in defiance of expectations,
that the universe growth is accelerating, contrary to what has always been
assumed that the expansion is slowing down due to gravity. In this paper a
general-relativistic cosmological theory that gives a direct relationship
between distances and redshifts in an expanding universe is presented. The
theory is actually a generalization of Hubble's law taking gravity into account
by means of Einstein's theory of general relativity. The theory predicts that
the universe can have three phases of expansion, decelerating, constant and
accelerating, but it is shown that at present the first two cases are excluded,
although in the past it had experienced them. Our theory shows that the
universe now is definitely in the stage of accelerating expansion, confirming
the recent experimental results.


title: Discovery of a New Supernova Remnant in the Direction of G69.7+1.0

abstract:
  We discovered a middle-aged supernova remnant (SNR) in the vicinity of
G69.7+1.0 using the ASCA satellite. G69.7+1.0 was identified in the 2.7 GHz
survey and classified as a shell-type SNR with a diameter of 16 arcmin. During
the ROSAT all-sky survey, the X-ray emission was detected in the direction of
G69.7+1.0. However, it extends beyond the radio shell, and an X-ray bright
region was located outside of the radio shell. A spectral study with the ASCA
and ROSAT shows a thin thermal plasma with an electron temperature of ~0.4 keV.
There is no significant variation of the spectral parameters over the field of
view, except for the lower column density of the eastern part. We also found a
large shell structure which surrounds the X-ray bright region in both optical
and radio images. We suggest that the observed X-ray emission is associated
with the large optical and radio shell, and that they are part of a new SNR,
different from the radio SNR G69.7+1.0, which we have named AX J2001+3235 or
G69.4+1.2. The large shell and the electron temperature of ~0.4 keV indicate
that AX J2001+3235 is an evolved SNR. From a comparison with the column density
of CTB 80 (G69.0+2.7), we estimate that the distance of the SNR is about 2.5
kpc.


title: First Results from the Heidelberg Dark Matter Search Experiment

abstract:
  The Heidelberg Dark Matter Search Experiment (HDMS) is a new ionization
Germanium experiment in a special design. Two concentric Ge crystals are housed
by one cryostat system, the outer detector acting as an effective shield
against multiple scattered photons for the inner crystal, which is the actual
dark matter target. We present first results after successfully running the
prototype detector for a period of about 15 months in the Gran Sasso
Underground Laboratory. We analyze the results in terms of limits on
WIMP-nucleon cross sections and present the status of the full scale
experiment, which will be installed in Gran Sasso in the course of this year.


title:
Spectroscopy of diffuse ionized gas in halos of selected edge-on
  galaxies

abstract:
  In order to examine the excitation and ionization mechanism of extraplanar
diffuse ionized gas (DIG) we have obtained optical longslit spectra of seven
edge-on spiral galaxies. In four objects the brightest emission lines can be
traced out to distances of typically 1.5 kpc above the disk. For NGC1963 and
NGC3044 line ratios such as [NII]6583/Ha or [SII]6717/Ha as well as
[OIII]5007/Hb could be measured for the halo DIG. This allows us to discuss the
DIG in the halo of these objects in the framework of diagnostic diagrams. For
these two objects, the line ratios of [OIII]5007/Hb decrease with increasing z,
different from the recently reported trend in NGC891 (Rand 1998). We find that
emission lines from the DIG in the disks are in good agreement with
photoionization models using a dilute radiation field. However, with increasing
z these models fail to predict the measured [OI]6300/Ha and HeI5876/Ha line
ratios for NGC1963. Diagnostic diagrams reveal for NGC1963 the need for a
second ionization mechanism of the halo DIG (besides photoionization). This
additional source could be shock ionization. The same diagrams demonstrate an
intermediate classification for NGC3044. Plots of [SII]/[NII] vs. emission
measure reveal significant changes towards the halo and seem to trace local
small scale density fluctuations of the extraplanar DIG.


title: Dynamical Evolution: Spirals and Bars

abstract:
  Non-axisymmetric modes like spirals and bars are the main driver of the
evolution of disks, in transferring angular momentum, and allowing mass
accretion. This evolution proceeds through self-regulation and feedback
mechanisms, such as bar destruction or weakening by a central mass
concentration, decoupling of a nuclear bar taking over the gas radial flows and
mass accretion, etc.. These internal mechanisms can also be triggered by
interaction with the environment. Recent problems are discussed, like the
influence of counter-rotation in the m=1 and m=2 patterns development and on
mass accretion by a central AGN.


title: Halo and Relic Sources in Clusters of Galaxies

abstract:
  New images of 7 radio halos and relics, obtained with the Very Large Array at
20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in
the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the
properties of the other clusters with radio halos, i.e. are luminous in X-rays,
have high temperature, and show recent merger processes. No diffuse sources are
detected in a sample of clusters showing at least a tailed radio galaxy within
300 kpc from the cluster center, indicating that the connection between tailed
radio galaxies and halos is not relevant. For these clusters we give limits to
the surface brightness and to the angular size of possible undetected diffuse
sources.


title: Flat radio-spectrum galaxies and BLLacs: Part I: core properties

abstract:
  This paper concerns the relationship of BLLacs and flat spectrum weak
emission-line galaxies. We compare the weak emission-line galaxies and the
BLLacs in a sample of 57 flat spectrum objects (Marcha et al. 1996), using
high-frequency radio and non-thermal optical flux densities, spectral indices
and polarization properties. We consider whether objects which are not
`traditional' BLLacs-due to their larger emission line strengths, and larger
CaII spectral breaks-are simply starlight diluted BLLacs. Their broad-band
spectral properties are consistent with this interpretation, but their radio
polarization may indicate more subtle effects. Comparison of the weak
emission-line galaxies and the BLLacs shows that, on average, the former have
steeper spectra between 8 and 43GHz, and are less polarized at 8.4GHz. This is
consistent with many of the weak-lined objects being at larger angles to the
line of sight than the BLLacs. In addition to this population, we indicate a
number of the weak emission-line galaxies which may be `hidden BLLacs':
relativistically boosted objects very close to the line of sight with an
apparently weak AGN.


title:
Thermal X-ray Emission and Cosmic Ray Production in Young Supernova
  Remnants

abstract:
  We have developed a simple model to investigate the modifications of the
hydrodynamics and non-equilibrium ionization X-ray emission in young supernova
remnants due to nonlinear particle acceleration. In nonlinear, diffusive shock
acceleration, the heating of the gas to X-ray emitting temperatures is strongly
coupled to the acceleration of cosmic ray ions. If the acceleration is
efficient and a significant fraction of the shock ram energy ends up in cosmic
rays, compression ratios will be higher and the shocked temperature lower than
test-particle, Rankine-Hugoniot relations predict. We illustrate how particle
acceleration impacts the interpretation of X-ray data using the X-ray spectra
of Kepler's remnant, observed by ASCA and RXTE. The thermal X-ray emission
provides important constraints on the efficiency of particle acceleration, in
complement to nonthermal emission. X-ray data from Chandra and XMM Newton, plus
radio observations, will be essential to quantify nonlinear effects.


title:
A new look at globular cluster colors in NGC 3311 and the case for
  exclusively metal-rich globular cluster systems

abstract:
  NGC 3311, the central cD galaxy in the Hydra cluster, was previously thought
to host the most metal-rich globular cluster system known. Ground-based
Washington photometry had indicated the almost complete absence of the
population of globular clusters near [Fe/H] ~ -1 dex, normally dominant in the
metallicity distribution functions of giant elliptical galaxies. Lacking the
normal metal-poor globular cluster population, NGC 3311 was an outstanding
exception among galaxies, not easily understood under any of the current
globular cluster formation scenarios. Our HST/WFPC2 data yield normal globular
cluster colors and hence metallicities for this galaxy. We find a bi-modal
color distribution with peaks at (V-I)=0.91 +/- 0.03 and 1.09 +/- 0.03,
corresponding to [Fe/H] ~ -1.5 and -0.75 dex (somewhat dependent on the choice
of the conversion relation between color and metallicity). We review the
evidence for exclusively metal-rich globular cluster systems in other galaxies
and briefly discuss the implications for our understanding of globular cluster
and galaxy formation.


title: X-ray Emission from Isolated Be Stars

abstract:
  I discuss the X-ray observations of Be stars, and how their properties
compare to non-emission B stars. I focus on several specific stars that show
high flux levels and variability but also report on several interesting survey
results. The Be X-ray properties are discussed in the context of wind-shock
X-ray emission from normal OB stars as well as in the context of general
mechanisms that have been proposed to explain the Be phenomenon. Finally, I
conclude with a discussion of the spectral diagnostics that will be available
from the new generation of X-ray telescopes.


title: Atomic and Molecular Gas near NGC3077: The Making of a New Dwarf Galaxy?

abstract:
  Using the IRAM 30m radio telescope we have mapped the tidal arm feature
south-east of NGC 3077 where we recently detected molecular gas in the CO (1-0)
and (2-1) transitions. We find that the molecular gas is much more extended
than previously thought (several kpc). The CO emission can be separated into at
least 3 distinct complexes with equivalent radii between 250pc and 700pc - the
newly detected complexes therefore range among the largest molecular complexes
in the local universe. Mass estimates based on virialization and employing an
X_CO factor yield a total mass for the complexes of order 4 x 10^7 M_sun, i.e.
more than the estimated molecular mass within NGC 3077 itself. This implies
that interactions between galaxies can efficiently remove heavy elements and
molecules from a galaxy and enrich the intergalactic medium. A comparison of
the distribution of HI and CO shows no clear correlation. However, CO is only
found in regions where the HI column density exceeds 1.1 x 10^21 cm^-2. HI
masses for the molecular complexes mapped are of the same order as the
corresponding molecular masses. Since the complexes have all the ingredients to
form stars in the future, we are thus presumably witnessing the birth of a
dwarf galaxy. This process may have dominated the creation of dwarf galaxies at
larger look-back times.


title: Orbit Fitting and Uncertainties for Kuiper Belt Objects

abstract:
  We present a procedure for determination of positions and orbital elements,
and associated uncertainties, of outer Solar System planets. The orbit-fitting
procedure is greatly streamlined compared to traditional methods because
acceleration can be treated as a perturbation to the inertial motion of the
body. These techniques are immediately applicable to Kuiper Belt Objects, for
which recovery observations are costly. Our methods produce positional
estimates and uncertainty ellipses even in the face of the substantial
degeneracies of short-arc orbit fits; the sole a priori assumption is that the
orbit should be bound or nearly so. We use these orbit-fitting techniques to
derive a strategy for determining Kuiper Belt orbits with a minimal number of
observations.


title:
Interstellar X-ray Absorption Spectroscopy of Oxygen, Neon, and Iron
  with the Chandra LETGS Spectrum of X0614+091

abstract:
  We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the
Chandra Low Energy Transmission Grating Spectrometer spectrum of the low mass
X-ray binary X0614+091. We measure the column densities in O and Ne, and find
direct spectroscopic constraints on the chemical state of the interstellar O.
These measurements probably probe a low-density line of sight through the
Galaxy and we discuss the results in the context of our knowledge of the
properties of interstellar matter in regions between the spiral arms.


title:
Intermittent behavior of cosmic mass field revealed by QSO's Ly_alpha
  forests

abstract:
  The intermittent behavior of the space-scale distribution of Ly$\alpha$
transmitted flux of QSO HS1700+64 has been analyzed via a discrete wavelet
transform. We found that there are strong indications of intermittency on
scales down to about 10 $h^{-1}$ kpc. These are: 1.) the probability
distribution function of the local fluctuations of the flux is significantly
long-tailed on small scales, and 2.) the local power spectrum of the flux shows
prominent spiky structures on small scales. Moreover, the local power spectrum
averaged on regions with different sizes shows similar spiky structures.
Therefore, the random mass density field traced by the Ly$\alpha$ forests is
rougher on smaller scales, consistent with singular clustering.