title: Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345

abstract:
  We investigate whether a pc-scale jet of 3C345 is dominated by a normal
plasma or an electron-positron plasma. We present a general condition that a
jet component becomes optically thick for synchrotron self-absorption, by
extending the method originally developed by Reynolds et al. The general
condition gives a lower limit of the electron number density, with the aid of
the surface brightness condition, which enables us to compute the magnetic
field density. Comparing the lower limit with another independent constraint
for the electron density that is deduced from the kinetic luminosity, we can
distinguish the matter content. We apply the procedure to the five components
of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes
at the peak frequencies were obtainable from literature. Evaluating the
representative values of Doppler beaming factors by their equipartition values,
we find that all the five components are likely dominated by an
electron-positron plasma. The conclusion does not depend on the lower cutoff
energy of the power-law distribution of radiating particles.


title: Generalised inflation with a gravitational wave background

abstract:
  We propose a Lambda-inflation model which explains a significant part of the
COBE signal by primordial cosmic gravitational waves. The primordial density
perturbations fulfill both the constraints of large-scale microwave background
and galaxy cluster normalization. The model is tested against the galaxy
cluster power spectrum and the high-multipole angular CMB anisotropy.


title: The Broad Band Spectrum of MXB 1728-34 Observed by BeppoSAX

abstract:
  We report on the results of a broad band (0.1-100 keV) spectral analysis of
the bursting atoll source MXB 1728-34 observed by the BeppoSAX satellite. Three
bursts were present during this observation. The spectrum during the bursts can
be fitted by a blackbody with a temperature of 2 keV. From the bursts we also
estimate a distance to the source of 5.1 kpc. MXB 1728-34 was in a rather soft
state during the BeppoSAX observation. The persistent spectrum is well fitted
by a continuum consisting of a soft blackbody emission and a comptonized
spectrum. We interpreted the soft component as the emission from the accretion
disk. Taking into account a spectral hardening factor of 1.7, we estimated that
the inner disk radius is $R_{\rm in} \sqrt{\cos i} \sim 20$ km, where i is the
inclination angle. The comptonized component could originate in a spherical
corona, with temperature of 10 keV and optical depth of 5, surrounding the
neutron star. A broad gaussian emission line at 6.7 keV is observed in the
spectrum, probably emitted in the ionized corona or in the inner part of the
disk. Another emission line is present at 1.66 keV.


title: Reconstructing the History of Star Formation in Rich Cluster Cores

abstract:
  We address the current crucial issues on the formation and evolution of
cluster galaxies: ie., connection between the Butcher-Oemler effect, assembly
of cluster galaxies, truncation of star formation, and the origin of S0
galaxies.
  We construct the field corrected colour-magnitude (CM) diagrams for 7 CNOC
clusters (0.23<z<0.43) and Coma, and illustrate the evolution of the complete
cluster population down to the present-day based on the model in which star
formation is truncated when the galaxies infall from the surrounding field.
  We show that the blue galaxies are incorporated into the present-day tight CM
relation as they fade and become redder after the truncation, which is possibly
responsible for producing faint S0's (>M*+1). Truncation of star formation is,
however, found to be relatively milder (with a time scale of 1 Gyr) than
suggested by the viorent processes such as ram-pressure stripping and/or
mergers/harassment.
  The BO effect is after all found to be a combination of three effects,
namely, increasing field star formation activity, increasing galaxy infall
rate, and the truncatin of star formation after the accretion. Our approach
naturally leads to the history of galaxy assembly and `global' star foramtion
for `cluster' galaxies.


title:
The X-ray transient XTE J1118+480: Multiwavelength observations of a
  low-state mini-outburst

abstract:
  We present multiwavelength observations of the newly discovered X-ray
transient XTE J1118+480 obtained in the rising phase of the 2000 April
outburst. This source is located at unusually high Galactic latitude and in a
very low absorption line of sight. This made the first EUVE spectroscopy of an
X-ray transient outburst possible. Together with our HST, RXTE, and UKIRT data
this gives unprecedented spectral coverage. We find the source in the low hard
state. The flat IR-UV spectrum appears to be a combination of optically thick
disk emission and flat spectrum emission, possibly synchrotron, while at higher
energies, including EUV, a typical low hard state power-law is seen. EUVE
observations reveal no periodic modulation, suggesting an inclination low
enough that no obscuration by the disk rim occurs. We discuss the nature of the
source and this outburst and conclude that it may be more akin to
mini-outbursts seen in GRO J0422+32 than to a normal X-ray transient outburst.


title:
Discovery of X-ray Emission from G328.4+0.2, a Crab-Like Supernova
  Remnant

abstract:
  G328.4+0.2 is a moderately small (5 arcmin x 5arcmin) Galactic radio
supernova remnant (SNR) at a distance of at least 17 kpc that has been long
suggested to be Crab-like. Here we report on the detection with ASCA of the
X-ray emission from the SNR. The X-ray source is faint with an observed flux of
(6.0 +/- 0.8)E-13 erg/s/cm^2 over the 2-10 keV band. The emission is heavily
cut-off at low energies and no flux is detected below 2 keV. Spectral analysis
confirms that the column density to the source is indeed large, N_H ~ 1E23
atoms/cm^2, and consistent with the total column density of hydrogen through
the Galaxy at this position. Good fits to the spectrum can be obtained for
either thermal plasma or nonthermal power-law models, although the lack of
detected line emission as well as other evidence argues against the former
interpretation. The power-law index we find, \alpha_P = 2.9 (+0.9,-0.8), is
consistent with other Crab-like SNRs. In the radio band G328.4+0.2 is nearly as
luminous as the Crab Nebula, yet in the X-ray band luminosity it is some 70
times fainter. Nevertheless its inferred soft X-ray band luminosity is greater
than all but the brightest pulsar-powered synchrotron nebulae and implies that
G328.4+0.2 contains a rapidly spinning, as yet undetected, pulsar that is
losing energy at a rate of approximately 1E38 erg/s.


title: Asteroids in the Inner Solar System I - Existence

abstract:
  Ensembles of in-plane and inclined orbits in the vicinity of the Lagrange
points of the terrestrial planets are integrated for up to 100 million years.
The integrations incorporate the gravitational effects of Sun and the eight
planets (Pluto is neglected). Mercury is the least likely planet, as it is
unable to retain tadpole orbits over 100 million year timescales. Both Venus
and the Earth are much more promising, as they possess rich families of stable
tadpole and horseshoe orbits. Our survey of Trojans in the orbital plane of
Venus is undertaken for 25 million years. Some 40% of the survivors are on
tadpole orbits. For the Earth, the integrations are pursued for 50 million
years. The stable zones in the orbital plane are larger for the Earth than for
Venus, but fewer of the survivors are tadpoles. Both Venus and the Earth also
have regions in which inclined test particles can endure near the Lagrange
points. For Venus, only test particles close to the orbital plane are stable.
For the Earth, there are two bands of stability, one at low inclinations (i <
16 degrees) and one at moderate inclinations (between 24 degrees and 34
degrees). The inclined test particles that evade close encounters are primarily
moving on tadpole orbits. Our survey of in-plane test particles near the
Martian Lagrange points shows no survivors after 60 million years. Low
inclination test particles do not persist, as their inclinations are quickly
increased until the effects of a secular resonance with Jupiter cause
de-stabilisation. Numerical integrations of inclined test particles for
timespans of 25 million years show stable zones for inclinations between 14 and
40 degrees.


title: Dense gas in the dust lane of Centaurus A

abstract:
  The interstellar medium of Centaurus A (NGC 5128) has been studied
extensively in recent years, using mostly molecular lines tracing low to medium
density gas (500 to several $10^3$ cm$^{-3}$). The amount and distribution of
the dense molecular gas was largely unknown. Here we present new millimeter
data of the HCN(1-0), CS(2-1), and CS(3-2) rotational transitions towards the
nearby radio galaxy Centaurus A observed with the SEST on La Silla, Chile. We
obtained spectra of the HCN(1-0) emission which traces dense 10$^4$ cm$^{-3}$
molecular gas at the center and along the prominent dust lane at offset
positions $\pm60^{\prime \prime}$ and $\pm100^{\prime \prime}$. We also
obtained a few spectra of CS(2-1) and (3-2) tracing densities of $\sim10^5$
cm$^{-3}$. The emission in these lines is weak and reaches a few mK at the
available angular resolutions of 54$^{\prime \prime}$ - 36$^{\prime \prime}$.
At the central position, the integrated intensity ratio I(HCN)/I(CO) peaks at
0.064, and decreases to $\sim$0.02 to 0.04 in the dust lane.


title:
Constrains on parameters of magnetic field decay for accreting isolated
  neutron stars

abstract:
  The influence of exponential magnetic field decay (MFD) on the spin evolution
of isolated neutron stars is studied. The ROSAT observations of several X-ray
sources, which can be accreting old isolated neutron stars, are used to
constrain the exponential and power-law decay parameters. We show that for the
exponential decay the ranges of minimum value of magnetic moment, $\mu_b$, and
the characteristic decay time, $t_d$, $\sim 10^{29.5}\ge \mu_b \ge 10^{28} {\rm
G} {\rm cm}^3$, $\sim 10^8\ge t_d \ge 10^7 {\rm yrs}$ are excluded assuming the
standard initial magnetic moment, $\mu_0=10^{30} {\rm G} {\rm cm}^3$. For these
parameters, neutron stars would never reach the stage of accretion from the
interstellar medium even for a low space velocity of the stars and a high
density of the ambient plasma. The range of excluded parameters increases for
lower values of $\mu_0$.
  We also show, that, contrary to exponential MFD, no significant restrictions
can be made for the parameters of power-law decay from the statistics of
isolated neutron star candidates in ROSAT observations.
  Isolated neutron stars with constant magnetic fields and initial values of
them less than $\mu_0 \sim 10^{29} {\rm G} {\rm cm}^3$ never come to the stage
of accretion.
  We briefly discuss the fate of old magnetars with and without MFD, and
describe parameters of old accreting magnetars.


title: Multi-Read Out Data Simulator

abstract:
  We present a data simulation package designed to create a series of simulated
data samples for a detector with non-destructive sampling capability. The
original intent of this software was to provide a method for generating
simulated images for the Next Generation Space Telescope, but it is general
enough to apply to almost any non-destructive detector or instrument.
MultiDataSim can be used to generate "practice" sampling strategies for an
instrument or field-of-view, and thus can be used to identify optimal
observation strategies.


title:
Removal of the calcium underabundance in cool metal rich Galactic disk
  dwarfs

abstract:
  An apparent Ca underabundance for cool metal rich disk dwarfs was derived by
Feltzing & Gustafsson (1998, A&AS, 129, 237). This was suggested to be a NLTE
effect, following the prediction by Drake (1991, MNRAS, 251, 369). New NLTE
calculations with MARCS atmospheres and opacities (Thor\'en, P., 2000, A&A, in
preparation) show that deviations from LTE are very small and can not explain
the underabundance. It is shown that the underabundance was primarily due to
erroneously calculated atomic line broadening parameters (van der Waals
broadening). Part of the underabundance was also due to the decision not to
change photometrically determined stellar parameters to satisfy the Fe I
excitation balance.


title: Asteroids in the Inner Solar System II - Observable Properties

abstract:
  This paper presents synthetic observations of long-lived, coorbiting
asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed by
taking the limiting semimajor axes, differential longitudes and inclinations
for long-lived stability provided by simulations. The intervals are randomly
populated with values to create initial conditions. These orbits are
re-simulated to check that they are stable and then re-sampled every 2.5 years
for 1 million years. The Mercurian sample contains only horseshoe orbits, the
Martian sample only tadpoles. For both Venus and the Earth, the greatest
concentration of objects on the sky occurs close to the classical Lagrange
points at heliocentric ecliptic longitudes of 60 and 300 degrees. The
distributions are broad especially if horseshoes are present in the sample. The
full-width half maximum (FWHM) in heliocentric longitude for Venus is 325
degrees and for the Earth is 328 degrees. The mean and most common velocity of
these coorbiting satellites coincides with the mean motion of the parent
planet, but again the spread is wide with a FWHM for Venus of 27.8 arcsec/hr
and for the Earth of 21.0 arcsec/hr. For Mars, the greatest concentration on
the sky occurs at heliocentric ecliptic latitudes of 12 degrees. The peak of
the velocity distribution occurs at 65 arcsec/hr, significantly less than the
Martian mean motion, while its FWHM is 32.3 arcsec/hr. The case of Mercury is
the hardest of all, as the greatest concentration occurs at heliocentric
longitudes close to the Sun.


title: Quintessence and CMB

abstract:
  A particular kind of quintessence is considered, with equation of motion
$p_Q/\rho_Q = -1$, corresponding to a cosmological term with time-dependence
$\Lambda(t) = \Lambda(t_0) (R(t_0)/R(t))^{P}$ which we examine initially for $0
\leq P < 3$. Energy conservation is imposed, as is consistency with big-bang
nucleosynthesis, and the range of allowed $P$ is thereby much restricted to $0
\leq P < 0.2$. The position of the first Doppler peak is computed analytically
and the result combined with analysis of high-Z supernovae to find how values
of $\Omega_m$ and $\Omega_{\Lambda}$ depend on $P$.


title: Radio Properties of the Supernova Remnant N157B

abstract:
  A new investigation of the supernova remnant (SNR) N157B was carried out with
the Australia Telescope Compact Array. Radio continuum images of the entire 30
Doradus region have been made at 3.5 and 6 cm wavelength with a resolution of
2". These data allow a high resolution study of the spectral index distribution
and polarization properties of both N157B and the nearby 30 Doradus nebula (the
latter will be reported in a subsequent paper). N157B is an extended Crab-type
SNR which may be beginning the transition to a composite remnant. There is
little apparent fine structure and the brightest radio region is several
parsecs from the probable position of the X-ray pulsar. The SNR has a radio
spectral index of -0.19 and is significantly polarized at 3.5 cm but not at
longer wavelengths.


title: FUSE Spectroscopy of High Velocity Cloud Complex C

abstract:
  We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the
sightline toward the Seyfert 1 galaxy Markarian 876, which passes through high
velocity cloud (HVC) complex C. This sight line demonstrates the ability of
FUSE to measure ionic absorption lines in Galactic HVCs. High velocity
absorption is clearly seen in both members of the O VI doublet. This is the
first detection of O VI in a neutral hydrogen HVC. One component of HVC complex
C is resolved in multiple Fe II lines from which we derive N(Fe II)/N(H I)=0.48
(Fe/H)_solar. This value of N(Fe II)/N(H I) implies that the metallicity of
complex C along this sightline may be higher than that along the Mrk 290
sightline (0.1 solar) found by Wakker et al. (1999). On the other hand, if the
metallicity of complex C is also 0.1 solar along this line of sight, the
observed value of N(Fe II)/(N(H I) suggests there may be a significan t amount
of H+ along the line of sight. In any case, little, if any, iron can be
depleted into dust grains if the intrinsic metallicity of complex C is
subsolar. Absorption from complex C is also seen in C II, N I, and N II, and
upper limits based on non-detections can be determined for Ar I, P II, and Fe
III. Although molecular hydrogen in the Milky Way is obvious in the FUSE data,
no H_2 absorption is seen in the high velocity cloud to a limit
N(H_2)<2.0x10^14 cm^-2. Future FUSE observations of extragalactic objects
behind Galactic high velocity clouds will allow us to better constrain models
of HVC origins.


title: Turbulence in the Solar Photosphere

abstract:
  The precise nature of photospheric flows, and of the transport effects they
give rise to, has been the subject of intense debate in the last decade. Here
we attempt to give a brief review of the subject emphasizing interdisciplinary
(solar physics - turbulence theory) aspects, key open questions, and recent
developments.


title: How to fool CMB parameter estimation

abstract:
  With the release of the data from the Boomerang and MAXIMA-1 balloon flights,
estimates of cosmological parameters based on the Cosmic Microwave Background
(CMB) have reached unprecedented precision. In this paper I show that it is
possible for these estimates to be substantially biased by features in the
primordial density power spectrum. I construct primordial power spectra which
mimic to within cosmic variance errors the effect of changing parameters such
as the baryon density and neutrino mass, meaning that even an ideal measurement
would be unable to resolve the degeneracy. Complementary measurements are
necessary to resolve this ambiguity in parameter estimation efforts based on
CMB temperature fluctuations alone.


title: Dynamics of Cosmic Necklaces

abstract:
  We perform numerical simulations of cosmic necklaces (systems of monopoles
connected to two strings each) and investigate the conditions under which
monopoles annihilate. When the total monopole energy is large compared to the
string energy, we find that the string motion is no longer periodic, and thus
the strings will be chopped up by self intersection. When the total monopole
energy is much smaller than the string energy, the string motion is periodic,
but that of the monopoles is not, and thus the monopoles travel along the
string and annihilate with each other.


title: The Solar Core and Solar Neutrinos

abstract:
  The long-standing deficit of measured versus predicted solar neutrino fluxes
is re-examined in light of possible astrophysical solutions. In the last
decade, solar neutrino flux and helioseismic measurements have greatly
strengthened the case for non-astrophysical solutions. But some model-
independent tests remain open.


title:
The Evolution of Magnetic Field and Spin Period of Accreting Neutron
  Stars

abstract:
  Based on the accretion induced magnetic a field decay model, in which a
frozen field and an incompressible fluid are assumed, we obtain the following
results. (1) An analytic relation between the magnetic field and spin period,
if the fastness parameter of the accretion disk is neglected.
  The evolutionary tracks of accreting neutron stars in the P-B diagram in our
model are different from the equilibrium period lines when the influence of the
fastness parameter is taken into account. (2) The theoretical minimum spin
period of an accreting neutron star is $\max (1.1{\rm ms}(\frac{\Delta
M}{M_{\odot}})^{-1} R^{-5/14}_6 I_{45}(\frac{M}{M_{\odot}})^{-1/2}, 1.1{\rm ms}
(\frac{M}{M_{\odot}})^{-1/2} R^{17/14}_6)$, independent of the accretion rate
(X-ray luminosity) but dependent on the total accretion mass $\Delta M$.
However, the minimum magnetic field depends on the accretion rate. (3) The
magnetic field strength decreases faster with time than the period.


title:
The Discovery of a Luminous z=5.80 Quasar from the Sloan Digital Sky
  Survey

abstract:
  We present observations of SDSSp J104433.04--012502.2, a luminous quasar at
z=5.80 discovered from Sloan Digital Sky Survey (SDSS) multicolor imaging data.
This object was selected as an i'-band dropout object, with i*=21.8 +/- 0.2,
z*=19.2 +/- 0.1. It has an absolute magnitude M1450 = -27.2 (H_0 =50 km/s/Mpc,
q0 = 0.5). The spectrum shows a strong and broad Ly alpha emission line, strong
Ly alpha forest absorption lines with a mean continuum decrement D_A = 0.91,
and a Lyman Limit System at z=5.72. The spectrum also shows strong OI and SiIV
emission lines similar to those of quasars at z<= 5, suggesting that these
metals were produced at redshift beyond six. The lack of a Gunn-Peterson trough
in the spectrum indicates that the universe is already highly ionized at z ~
5.8. Using a high-resolution spectrum in the Ly alpha forest region, we place a
conservative upper limit of the optical depth due to the Gunn-Peterson effect
of tau < 0.5 in regions of minimum absorption. The Ly alpha forest absorption
in this object is much stronger than that in quasars at z<= 5. The object is
unresolved in a deep image with excellent seeing, implying that it is unlensed.
The black hole mass of this quasar is ~3 x 10^9 M_solar if we assume that it is
radiating at the Eddington luminosity and no lensing amplification, implying
that it resides in a very massive dark matter halo. The discovery of one quasar
at M_1450 < -27 in a survey area of 600 deg^2 is consistent with an
extrapolation of the observed luminosity function at lower redshift. The
abundance and evolution of such quasars can provide sensitive tests of models
of quasar and galaxy formation.


title:
Can EGRET's Gamma Ray Sources > 100 MeV Be Seen with Single Secondary
  Cosmic Muons from Gammas > 30 GeV?

abstract:
  The high energy gamma ray sources provided by experiment EGRET on the Compton
Gamma Ray Observatory are examined, testing Project GRAND's ability to detect
primary gamma rays by means of studying secondary muons. There is ~1.5% chance
that a 100 GeV primary cosmic gamma ray will produce a muon at detection level
(Fasso & Poirier, 1999), a probability which increases with increasing gamma
energy. Project GRAND has 80 square meters of muon detector which identifies
secondary muons >0.1 GeV and measures their angles to 0.26 deg (projected angle
in the XZ and YZ planes). Data taken during the last two years are analyzed. A
table of EGRET's gamma ray sources is examined (The Third EGRET Catalog of High
Energy Gamma Ray Sources (EGRET webpage, 1999). EGRET's flux (>0.1 GeV),
angular information, and spectral index were extrapolated to GRAND's energy
region (>30 GeV). Then the geometrical acceptance was calculated for each of
these events. Thus, GRAND's sensitivity to each of EGRET's sources was
predicted. A product of extrapolated flux and GRAND's detection sensitivity
yields an overall parameter indicating GRAND's relative sensitivity to each
source, assuming an energy dependence given by EGRET's spectral index. The 14
sources with the best extrapolated detection efficiency were selected to be
examined with the data.


title:
Confirmation of a moving component in the H-alpha emission line of
  LSI+61303

abstract:
  We report our attempts to detect and confirm a narrow moving component in the
H-alpha emission line of the radio emitting Be/X-ray binary LSI+61 303 (V615
Cas, GT0236+610). The existence of this spectral feature was already suspected
in the past. As a result, we find that this component does exist and that its
radial velocity varies in agreement with the radio period of the system. We
interpret it tentatively as due to a denser region, or bulge, orbiting near the
outer edge of the H-alpha emitting disk.


title:
Could the Unusual Optical Afterglow of GRB 000301c Arise from a
  Non-relativistic Shock with Energy Injection?

abstract:
  Recent observations on the GRB 000301c afterglow show that three breaks
appear in the R-band light curve, and in particular the decay slope at late
times is as steep as -3.0. This unusual afterglow is clearly inconsistent with
the standard afterglow shock model. Here we propose a non-standard model for
the unusual R-band afterglow of GRB 000301c. In this model, an
ultra-relativistic shock in a dense medium ("dirty environment")rapidly evolved
to the non-relativistic phase in initial 1 day. During such a phase, the shock
happened to be caught up with by two energetic shells ejected from the central
engine at two different times, and the shock was refreshed, leading to two
flattenings of the light curve. After each interaction between the shock and
shell, the afterglow decayed as $\propto t^{-3.0}$ if the electron distribution
index of the shocked medium, $p\approx 3.4$, derived from the optical spectrum.
Therefore, this model can provide an excellent explanation for the flattening
and steepening features of the GRB 000301c optical afterglow light curve. We
further point out that the energy injection shells ejected from the central
engine at later times may be material shells (e.g., in the massive star
progenitor models related to black holes) or radiation shells (e.g., in the
millisecond pulsar progenitor models).


title: The parallax distorsion via a weak microlensing effect

abstract:
  Parallax measurements allow distances to celestial objects to be determined.
Coupled with measurement of their position on the celestial sphere, it gives a
full three-dimensional picture of the location of the objects relative to the
observer. The distortion of the parallax value of a remote source affected by a
weak microlensing is considered. This means that the weak microlensing leads to
distortion of the distance scale. It is shown that the distortions to appear
may change strongly the parallax values in case they amount to several
microseconds of arc. In particular, at this accuracy many measured values of
the parallaxes must be negative.


title:
Antiprotons Annihilation in the Galaxy As A Source of Diffuse Gamma
  Background

abstract:
  The existence of antimatter domains in baryon asymmetrical Universe can
appear as the cosmological consequence of particle theory in inflationary
models with non-homogeneous baryosynthesis. Such a domain can survive in the
early Universe and form globular cluster of antimatter stars in our Galaxy. The
model of antimatter pollution of Galaxy and annihilation with matter gas is
developed. The proton-antiproton annihilation gamma flux is shown to reproduce
the observed galactic gamma background measured by EGRET. From comparison with
observational data the estimation on the maximally allowed amount of antimatter
stars, possibly present in our Galaxy, is found.


title:
Galactic Observations at 31, 42 and 144~GHz with the Mobile Anisotropy
  Telescope

abstract:
  We present multi-frequency maps of a portion of the Galactic Plane centered
on a declination of -60 degrees with resolutions ranging from 0.2 to 0.9
degrees. The maps are optimized to detect unresolved source emission and are
cross-calibrated against the planet Jupiter. We discuss six millimeter-bright
regions, three of which are visible in all bands, and list measured flux
densities. Variability is limited to less than 3.8% for all sources seen at 31
and 42 GHz and less than 10% at 144 GHz. Fractional polarization limits smaller
than 0.08 are measured for all sources seen at 31 and 42 GHz. No fractional
polarization limits are reported at 144 GHz.


title:
Gamma-Ray Emissions from Pulsars: Spectra of the TEV Fluxes from
  Outer-Gap Accelerators

abstract:
  We study the gamma-ray emissions from an outer-magnetospheric potential gap
around a rotating neutron star. Migratory electrons and positrons are
accelerated by the electric field in the gap to radiate copious gamma-rays via
curvature process. Some of these gamma-rays materialize as pairs by colliding
with the X-rays in the gap, leading to a pair production cascade. Imposing the
closure condition that a single pair produces one pair in the gap on average,
we explicitly solve the strength of the acceleration field and demonstrate how
the peak energy and the luminosity of the curvature-radiated, GeV photons
depend on the strength of the surface blackbody and the power-law emissions.
Some predictions on the GeV emission from twelve rotation-powered pulsars are
presented. We further demonstrate that the expected pulsed TeV fluxes are
consistent with their observational upper limits. An implication of high-energy
pulse phase width versus pulsar age, spin, and magnetic moment is discussed.


title:
ROSAT/ASCA Observations of a Serendipitous BL Lac Object PKS 2316-423:
  The Variable High-Energy Tail of Synchrotron Radiation

abstract:
  We present the analysis of archival data from ROSAT and ASCA of a
serendipitous BL Lac object PKS 2316-423. Because of its featureless
non-thermal radio/optical continuum, PKS 2316-423 has been called as a BL Lac
candidate in the literature. PKS 2316-423 was evidently variable over the
multiple X-ray observations, in particular, a variable high-energy tail of the
synchrotron radiation is revealed. The X-ray spectral analysis provides further
evidence of the synchrotron nature of its broad-band spectrum: a steep and
downward curving spectrum between 0.1--10 keV, typical of high-energy peaked BL
Lacs (HBL). The spectral energy distribution (SED) through radio-to-X-ray
yields the synchrotron radiation peak at frequency Vp=7.3 10^{15} Hz, with
integrated luminosity of Lsyn=2.1 10^{44} ergs s^{-1}. The averaged SED
properties of PKS 2316-423 are very similar to those ``intermediate'' BL Lac
objects (IBL) found recently in several deep surveys, such as Deep X-ray Radio
Blazar, Radio-Emitting X-ray, and ROSAT-Green Bank surveys. We suggest that PKS
2316-423 is an IBL though it also shows some general features of a HBL.
Actually, this double attribute of PKS 2316-423 provides a good test of the
prediction that an IBL object can show either synchrotron or inverse-Compton
characteristics in different variability states.


title: On cooling flows and the Sunyaev-Zel'dovich effect

abstract:
  We study the effect of cooling flows in galaxy clusters on the
Sunyaev-Zel'dovich (SZ) distortion and the possible cosmological implications.
The SZ effect, alongwith X-ray observations of clusters, is used to determine
the Hubble constant, $H_{\circ}$. Blank sky surveys of SZ effect are being
planned to constrain the geometry of the universe through cluster counts. It is
also known that a significant fraction of clusters has cooling flows in them,
which changes the pressure profile of intracluster gas. Since the SZ decrement
depends essentially on the pressure profile, it is important to study possible
changes in the determination of cosmological parameters in the presence of a
cooling flow. We build several representative models of cooling flows and
compare the results with the corresponding case of gas in hydrostatic
equilibrium. We find that cooling flows can lead to an overestimation of the
Hubble constant. Specifically, we find that for realistic models of cooling
flow with mass deposition (varying $\dot m$ with radius), there is of the order
$\sim 10 %$ deviation in the estimated value of the Hubble constant (from that
for gas without a cooling flow) even after excluding $ \sim 80 %$ of the
cooling flow region from the analysis. We also discuss the implications of
using cluster counts from SZ observations to constrain other cosmological
parameters, in the presence of clusters with cooling flows.


title:
Near-infrared adaptive optics observations of galaxy clusters: Abell 262
  at z=0.0157, J1836.3CR at z=0.414, and PKS 0743-006 at z=0.994

abstract:
  We report on high angular resolution near-infrared (NIR) observations of
three galaxy clusters at different redshifts using adaptive optics (AO). In the
case of the barred spiral \object{UGC 1347} in Abell 262 we presented the first
AO results obtained using a laser guide star. The observations have been
carried out with the MPE/MPIA adaptive optics laser guide star system ALFA and
the ESO AO system ADONIS combined with the SHARP II+ camera built at MPE. The
three clusters are well suited for high resolution investigations since bright
field stars for tip-tilt or wavefront sensing are located close to the line of
sight to cluster galaxies. In summary our high angular resolution NIR data
combined with other information clearly indicates star formation activity or
interaction between cluster members at all three redshifts. The results and
implications for future high angular resolution adaptive optics observations
are discussed in the framework of current galaxy and cluster evolution models.


title:
The role of NCO reaction chain on the He ignition in degenerate stellar
  structures

abstract:
  The role played by NCO reaction in the onset of the He flash in the He core
of a RGB star and in low mass CO WDs accreting H/He rich matter is
investigated.


title:
Spectroscopic confirmation of a white dwarf companion to the B star 16
  Dra

abstract:
  Using an Extreme Ultraviolet Explorer (EUVE) spectrum, we confirm the
identification of a white dwarf companion to the B9.5V star 16 Dra (HD150100),
and constrain its surface temperature to lie between 29,000K and 35,000K. This
is the third B star + white dwarf non-interacting Sirius-type binary to be
confirmed, after y Pup (HR2875, HD59635) and theta Hya (HR3665, HD79469). 16
Dra and its white dwarf companion are members of a larger resolved proper
motion system including the B9V star 17 Dra A (HD150117). The white dwarf must
have evolved from a progenitor more massive than this star, i.e. ~3.7 solar
masses. White dwarf companions to B stars are important since they set an
observational limit on the maximum mass for white dwarf progenitors, and can
potentially be used to investigate the high mass ends of the initial-final mass
relation and the white dwarf mass-radius relation.


title: Stellar Populations in the Nucleus of NGC 6764

abstract:
  We present first results of near-infrared integral field spectroscopy of the
central 8''$\times$8'' of the Wolf-Rayet nucleus of the barred spiral galaxy
NGC 6764. In addition to stellar CO and Na I absorption lines as well as
recombination lines of H and He I the K-band spectrum shows strong emission
from molecular hydrogen. Analysis of the stellar nuclear light using population
synthesis in conjunction with NIR spectral synthesis suggests either the
presence of two starbursts with ages of $\sim$ 5 Myrs and $\sim$ 20 Myrs or
continuous star formation with an star formation rate of $\sim$ 0.4 \solm
yr^{-1} over the past 1 Gyr.


title:
Exhaustive Study of Cosmic Microwave Background Anisotropies in
  Quintessential Scenarios

abstract:
  Recent high precision measurements of the CMB anisotropies performed by the
BOOMERanG and MAXIMA-1 experiments provide an unmatched set of data allowing to
probe different cosmological models. Among these scenarios, motivated by the
recent measurements of the luminosity distance versus redshift relation for
type Ia supernovae, is the quintessence hypothesis. It consists in assuming
that the acceleration of the Universe is due to a scalar field whose final
evolution is insensitive to the initial conditions. Within this framework we
investigate the cosmological perturbations for two well-motivated potentials:
the Ratra-Peebles and the SUGRA tracking potentials. We show that the solutions
of the perturbed equations possess an attractor and that, as a consequence, the
insensitivity to the initial conditions is preserved at the perturbed level.
Then, we study the predictions of these two models for structure formation and
CMB anisotropies and investigate the general features of the multipole moments
in the presence of quintessence. We also compare the CMB multipoles calculated
with the help of a full Boltzmann code with the BOOMERanG and MAXIMA-1 data. We
pay special attention to the location of the second peak and demonstrate that
it significantly differs from the location obtained in the cosmological
constant case. Finally, we argue that the SUGRA potential is compatible with
all the recent data with a standard values of the cosmological parameters. In
particular, it fits the MAXIMA-1 data better than a cosmological constant or
the Ratra-Peebles potential.


title:
The discovery of quiescent X-ray emission from SAX J1808.4-3658, the
  transient 2.5ms pulsar

abstract:
  We report on a 20 ks BeppoSAX observation of the transient 2.5 ms X-ray
pulsar SAX J1808.4-3658 in its quiescent state. A source at a level of ~ 3 x
10^-3 c/s was detected with the BeppoSAX/MECS at a position consistent with
that of SAX J1808.4-3658. The inferred 0.5-10 keV luminosity was to that
measured from other quiescent low mass X-ray transients hosting an old neutron
star. This result is discussed in the light of the propeller and radio pulsar
shock emission models for the quiescent emission of these systems.


title: An Overview of the SPOrt Experiment

abstract:
  The Sky Polarization Observatory is an experiment selected by ESA for the
Early Opportunity Phase onboard the International Space Station. SPOrt is the
first payload specifically designed for polarization measurements, it will
provide near full sky maps of the sky polarized emission at four microwave
frequencies between 22 and 90 GHz. Current design of SPOrt will be presented,
together with an overview of the scientific goals of the experiment.


title: Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14

abstract:
  We present evidence of a 6.4 keV emission line during a burst from the soft
gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE)
monitored this source extensively during its outburst in the summer of 1998. A
strong burst observed on August 29, 1998 revealed a number of unique
properties. The burst exhibits a precursor and is followed by a long (~ 1000 s)
tail modulated at the 5.16 s stellar rotation period. The precursor has a
duration of 0.85 s and shows both significant spectral evolution as well as an
emission feature centered near 6.4 keV during the first 0.3 s of the event,
when the X-ray spectrum was hardest. The continuum during the burst is well fit
with an optically thin thermal bremsstrahlung (OTTB) spectrum with the
temperature ranging from about 40 to 10 keV. The line is strong, with an
equivalent width of 400 eV, and is consistent with Fe K-alpha fluorescence from
relatively cool material. If the rest-frame energy is indeed 6.4 keV, then the
lack of an observed redshift indicates that the source is at least 80 km above
the neutron star surface. We discuss the implications of the line detection in
the context of models for SGRs.


title: The Robustness of Inflation to Changes in Super-Planck-Scale Physics

abstract:
  We calculate the spectrum of density fluctuations in models of inflation
based on a weakly self-coupled scalar matter field minimally coupled to
gravity, and specifically investigate the dependence of the predictions on
modifications of the physics on length scales smaller than the Planck length.
These modifications are encoded in terms of modified dispersion relations.
Whereas for some classes of dispersion relations the predictions are unchanged
compared to the usual ones which are based on a linear dispersion relation, for
other classes important differences are obtained, involving tilted spectra,
spectra with exponential factors and with oscillations. We conclude that the
predictions of inflationary cosmology in these models are not robust against
changes in the super-Planck-scale physics.


title:
X-Ray and Optical Variability in NGC 4051 and the Nature of Narrow-Line
  Seyfert 1 Galaxies

abstract:
  We report on the results of a three-year program of coordinated X-ray and
optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid
continuum variations observed in the X-ray spectra are not detected in the
optical, although the time-averaged X-ray and optical continuum fluxes are
well-correlated. Variations in the flux of the broad Hbeta line are found to
lag behind the optical continuum variations by 6 days (with an uncertainty of
2-3 days), and combining this with the line width yields a virial mass estimate
of about 1.1 million solar masses, at the very low end of the distribution of
AGN masses measured by line reverberation. Strong variability of He II 4686 is
also detected, and the response time measured is similar to that of Hbeta, but
with a much larger uncertainty. The He II 4686 line is almost five times
broader than Hbeta, and it is strongly blueward asymmetric, as are the
high-ionization UV lines recorded in archival spectra of NGC 4051. The data are
consistent with the Balmer lines arising in a low to moderate inclination
disk-like configuration, and the high-ionization lines arising in an outflowing
wind, of which we observe preferentially the near side. Previous observations
of the narrow-line region morphology of this source suggest that the system is
inclined by about 50 degrees, and if this is applicable to the broad
Hbeta-emitting region, a central mass of about 1.4 million solar masses can be
inferred. During the third year of monitoring, both the X-ray continuum and the
He II 4686 line went into extremely low states, although the optical continuum
and the Hbeta broad line were both still present and variable. We suggest that
the inner part of the accretion disk may have gone into an advection-dominated
state, yielding little radiation from the hotter inner disk.


title: The Detection of Wind Variability in Magellanic Cloud O Stars

abstract:
  We present Far Ultraviolet Explorer (FUSE) spectra for three Magellanic Cloud
O stars (Sk 80, Sk -67 05 and Sk -67 111) with repeated observations. The data
demonstrate the capabilities of FUSE to perform time-resolved spectroscopy on
extragalactic stars. The wavelength coverage of FUSE provides access to
resonance lines due to less abundant species, such as sulfur, which are
unsaturated in O supergiants. This allows us to examine wind variability at all
velocities in resonance lines for stars with higher mass loss rates than can be
studied at longer (lambda > 1150 A) wavelengths. The FUSE wavelength range also
includes resonance lines from ions which bracket the expected dominant
ionization stage of the wind. Our observations span 1-4 months with several
densely sampled intervals of 10 hours or more. These observations reveal wind
variability in all of the program stars and distinctive differences in the
ionization structure and time scales of the variability. Sk -67 111
demonstrates significant wind variability on a time scale less than 10 hours
and the coolest O star (Sk -67 05) exhibits the largest variations in O VI.


title:
An Exploration of the Paradigm for the 2-3 Hour Period Gap in
  Cataclysmic Variables

abstract:
  We critically examine the basic paradigm for the origin of the 2-3 hr period
gap in cataclysmic variables (CVs). We carry out an extensive population
synthesis study of CVs starting from ~ 3 x 10^6 primordial binaries, and
evolving some ~ 2 x 10^4 surviving systems through their CV phase. In
particular we study current-epoch distributions of CVs in the $\dot M-P_{orb}$,
R_{2}-P_{orb}, M_{2}-P_{orb}, q-P_{orb}, T_{eff}-P_{orb}, and L_{2}-P_{orb}
planes, where $\dot M$ is the mass transfer rate, q is the mass ratio M_2/M_1,
and M_2, R_2, T_{eff}, and L_2 are the donor star mass, radius, effective
temperature, and luminosity, respectively. This work presents a new perspective
on theoretical studies of the long-term evolution of CVs. In particular, we
show that if the current paradigm is correct, the secondary masses in CVs just
above the period gap should be as much as ~ 50% lower than would be inferred if
one assumes a main-sequence radius-mass relation for the donor star.


title: The (anti)correlation of the sub-mm and X-ray background sources

abstract:
  The connection between the sub-mm and the hard X-ray backgrounds is studied
by comparing data at 2-10 keV and at 850um for a sample of 34 sources at fluxes
(or limiting fluxes) which resolve most of the background in the two bands.
These data were obtained with new SCUBA observations and by correlating data
sets available from the literature. None of the 11 hard X-ray (2-10 keV)
sources has a counterpart at 850um, with the exception of a faint Chandra
source, which is a candidate type 2 QSO at high redshift. These data indicate
that 2-10 keV sources brighter than 10^-15 erg s-1 cm-2, which make at least
75% of the background in this band, contribute for less than 7% to the
submillimetric background. Out of the 24 SCUBA sources 23 are undetected by
Chandra. These data indicate that most of these SCUBA sources must be powered
either by starburst activity, or by an AGN which is obscured by a column Nh >
10^25 cm-2, with a reflection efficiency in the hard X-rays significantly lower
than 1% in most cases.


title:
Light Element Abundance Patterns in the Orion Association: I) HST
  Observations of Boron in G-dwarfs

abstract:
  The boron abundances for two young solar-type members of the Orion
association, BD -6 1250 and HD 294297, are derived from HST STIS spectra of the
B I transition at 2496.771 A. The best-fit boron abundances for the target
stars are 0.13 and 0.44 dex lower than the solar meteoritic value of log
e(B)=2.78. An anticorrelation of boron and oxygen is found for Orion when these
results are added to previous abundances obtained for 4 B-type stars and the
G-type star BD -5 1317. An analysis of the uncertainties in the abundance
calculations indicates that the observed anticorrelation is probably real. The
B versus O relation observed in the Orion association does not follow the
positive correlation of boron versus oxygen which is observed for the field
stars with roughly solar metallicity. The observed anticorrelation can be
accounted for by a simple model in which two poorly mixed components of gas
(supernova ejecta and boron-enriched ambient medium) contribute to the new
stars that form within the lifetime of the association. This model predicts an
anticorrelation for Be as well, at least as strong as for boron.


title:
Spherically Symmetric Simulation with Boltzmann Neutrino Transport of
  Core Collapse and Post-Bounce Evolution of a 15 Solar Mass Star

abstract:
  We present a spherically symmetric, Newtonian core-collapse simulation of a
15 solar mass star with a 1.28 solar mass iron core. The time-, energy-, and
angle-dependent transport of electron neutrinos and antineutrinos was treated
with a new code which iteratively solves the Boltzmann equation and the
equations for neutrino number, energy and momentum to order O(v/c) in the
velocity v of the stellar medium. The supernova shock expands to a maximum
radius of 350 km instead of only about 240 km as in a comparable calculation
with multi-group flux-limited diffusion (MGFLD) by Bruenn, Mezzacappa, & Dineva
(1995). This may be explained by stronger neutrino heating due to the more
accurate transport in our model. Nevertheless, after 180 ms of expansion the
shock finally recedes to a radius around 250 km (compared to about 170 km in
the MGFLD run). The effect of an accurate neutrino transport is helpful, but
not large enough to cause an explosion of the considered 15 solar mass star.
Therefore postshock convection and/or an enhancement of the core neutrino
luminosity by convection or reduced neutrino opacities in the neutron star seem
necessary for neutrino-driven explosions of such stars. We find an electron
fraction Y_e > 0.5 in the neutrino-heated matter, which suggests that the
overproduction problem of neutron-rich nuclei with mass numbers around A = 90
in exploding models may be absent when a Boltzmann solver is used for the
electron neutrino and antineutrino transport.


title:
Detecting Ultra High Energy Neutrinos by Upward Tau Airshowers and Gamma
  Flashes

abstract:
  Tau Air-showers are the best trace of rarest Ultra High Energy neutrinos UHE
$\nu_{\tau}$, $\bar\nu_{\tau}$ and $\bar{\nu}_e$ at PeV and higher energy.
$\tau$ Air-showers may generate billion times amplified signals by their
secondaries . Horizontal amplified $\tau$ air-showers by $\nu_{\tau} N$ and UHE
$\bar\nu_{e} e$ at PeV emerging from mountain chain might be the most
power-full imprint. Upward UHE $\nu_{\tau} N$ interaction on Earth crust at
horizontal edge and from below, their consequent UHE $\tau$ air-showers beaming
toward high mountains should flash $\gamma$,$\mu$,X and optical detectors on
the top.
  Upward $\tau$ air-shower may hit nearby satellite flashing them by short,
hard, diluted $\gamma-$burst at the edge of Gamma Ray Observatory BATSE
threshold. We identify these events with recent (1994) discovered upward
Terrestrial Gamma Flashes (TGF) and we probed their UHE $\tau$ - UHE $\nu_\tau$
origin. From these TGF data approximated UHE $\nu_\tau$ flux and $\Delta
m_{\nu_\mu \nu_\tau}$ sever lower bound are derived. Partial TGF Galactic
signature is also manifest within known 47 TGF events clustered within three
degrees from the Galactic plane at ${\simeq 2\cdot 10^{-3}}$probability. Well
known $X-\gamma-\mathrm{TeV}$ active galactic and extragalactic sources have
found probable counterpart in TGF arrival directions. Detection of elusive UHE
$\nu_\tau$ seem finally achieved.


title:
Neutrino, Neutron, and Cosmic Ray Production in the External Shock Model
  of Gamma Ray Bursts

abstract:
  The hypothesis that ultra-high energy (>~ 10^19 eV) cosmic rays (UHECRs) are
accelerated by gamma-ray burst (GRB) blast waves is assumed to be correct.
Implications of this assumption are then derived for the external shock model
of gamma-ray bursts. The evolving synchrotron radiation spectrum in GRB blast
waves provides target photons for the photomeson production of neutrinos and
neutrons. Decay characteristics and radiative efficiencies of the neutral
particles that escape from the blast wave are calculated. The diffuse
high-energy GRB neutrino background and the distribution of high-energy GRB
neutrino events are calculated for specific parameter sets, and a scaling
relation for the photomeson production efficiency in surroundings with
different densities is derived. GRBs provide an intense flux of high-energy
neutrons, with neutron-production efficiencies exceeding ~ 1% of the total
energy release. The radiative characteristics of the neutron beta-decay
electrons from the GRB "neutron bomb" are solved in a special case. Galaxies
with GRB activity should be surrounded by radiation halos of ~ 100 kpc extent
from the outflowing neutrons, consisting of a nonthermal optical/X-ray
synchrotron component and a high-energy gamma-ray component from
Compton-scattered microwave background radiation. The luminosity of sources of
GRBs and relativistic outflows in L* galaxies such as the Milky Way is at the
level of ~10^40+-1 ergs/s. This is sufficient to account for UHECR generation
by GRBs. We briefly speculate on the possibility that hadronic cosmic rays
originate from the subset of supernovae that collapse to form relativistic
outflows and GRBs. (abridged)


title:
Constraining the cosmic equation of state from old galaxies at high
  redshift

abstract:
  New limits on the cosmic equation of state are derived from age measurements
of three recently reported old high redshift galaxies (OHRG). The results are
based on a flat FRW type cosmological model driven by nonrelativistic matter
plus a smooth component parametrized by its equation of state $p_{x} =
\omega\rho_{x}$ ($\omega \geq -1$). The range of $\omega$ is strongly dependent
on the matter density parameter. For $\Omega_{M} \sim 0.3$, as indicated from
dynamical measurements, the age estimates of the OHRG restricts the cosmic
parameter to $\omega\leq - 0.27$. However, if $\Omega_{M}$ is the one suggested
by some studies of field galaxies, i.e, $\Omega_{M} \simeq 0.5$, only a
cosmological constant ($\omega=-1$) may be compatible with these data.


title: The Effect of the Cosmic Web on Cluster Weak Lensing Mass Estimates

abstract:
  In modern hierarchical theories of structure formation, rich clusters of
galaxies form at the vertices of a weblike distribution of matter, with
filaments emanating from them to large distances and with smaller objects
forming and draining in along these filaments. The amount of mass contained in
structure near the cluster can be comparable to the collapsed mass of the
cluster itself. As the lensing kernel is quite broad along the line of sight
around cluster lenses with typical redshifts near z=0.5, structures many Mpc
away from the cluster are essentially at the same location as the cluster
itself, when considering their effect on the cluster's weak lensing signal. We
use large-scale numerical simulations of structure formation in a
Lambda-dominated cold dark matter model to quantify the effect that large-scale
structure near clusters has upon the cluster masses deduced from weak lensing
analysis. A correction for the scatter in possible observed lensing masses
should be included when interpreting mass functions from weak lensing surveys.


title: Gamma-ray burst afterglows as probes of galactic and intergalactic dust

abstract:
  The amount and properties of high-redshift galactic and intergalactic (IG)
dust are largely unknown, but could be investigated using multi-wavelength
photometry of high-z objects that have a known intrinsic spectrum. Observations
of gamma-ray burst (GRB) afterglows appear to support the theoretical model of
an adiabatic blast wave expanding into an external medium. In this model, the
synchrotron peak flux is independent of frequency, providing a flat spectrum
when observed over time, and therefore allowing straightforward measurement of
the relative attenuation of afterglow flux in widely separated bands. Applying
this method to dust extinction, we show that for a sample of afterglows which
have been corrected by galactic extinction, comparison between the number
counts of peak fluxes in X-ray versus optical can provide constraints on an
intergalactic component of dust. A similar technique can probe the
redshift-dependence of extinction in GRB-forming regions without requiring an
assumed relation between extinction and reddening by the dust. Probing
systematic changes in extinction with redshift - particularly in IG and/or
non-reddening dust - is crucial to a proper interpretation of the Type Ia
Supernova Hubble diagram and similar observations, and useful in understanding
GRB progenitor environments.


title: Properties of Cosmic Shock Waves in Large Scale Structure Formation

abstract:
  We have examined the properties of shock waves in simulations of large scale
structure formation for two cosmological scenarios (a SCDM and a LCDM with
Omega =1). Large-scale shocks result from accretion onto sheets, filaments and
Galaxy Clusters (GCs) on a scale of circa 5 Mpc/h in both cases. Energetic
motions, both residual of past accretion history and due to current asymmetric
inflow along filaments, generate additional, common shocks on a scale of about
1 Mpc/h, which penetrate deep inside GCs. Also collisions between substructures
inside GCs form merger shocks. Consequently, the topology of the shocks is very
complex and highly connected. During cosmic evolution the comoving shock
surface density decreases, reflecting the ongoing structure merger process in
both scenarios. Accretion shocks have very high Mach numbers (10-10^3), when
photo-heating of the pre-shock gas is not included. The typical shock speed is
of order v_{sh}(z) =H(z)lambda_{NL}(z), with lambda_{NL}(z) the wavelength
scale of the nonlinear perturbation at the given epoch. However, the Mach
number for shocks occuring within clusters is usually smaller (3-10), due to
the fact that the intracluster gas is already hot. Statistical fits of shock
speed around GCs as a function of GCs temperature give power-law's in accord
with 1-D predictions. However, a very different result is obtained for fits of
the shock radius, reflecting the very complex shock structures forming in 3-D
simulations. The in-flowing kinetic energy across such shocks, giving the power
available for cosmic-ray acceleration, is comparable to the cluster X-ray
luminosity emitted from a central region of radius 0.5 Mpc/h. Considering their
large size and long lifetimes, those shocks are potentially interesting sites
for cosmic-ray acceleration, if modest magnetic fields exist within them.


title:
Acceleration of CR at Large Scale Shocks and Their Cosmological Role for
  Structure Formation in the Universe

abstract:
  We investigate the dynamical importance of a newly recognized possible source
of significant feedback generated during structure formation; namely cosmic ray
(CR) pressure. We present evidence for the existence of numerous shocks in the
hot gas of galaxy clusters (GCs). We employ for the first time an explicit
numerical treatment of CR acceleration and transport in hydro simulations of
structure formation. According to our results, CRs provide an important
fraction of the total pressure inside GCs, up to several tenths. This was true
even at high redshift (z=2), meaning that such non-thermal component could
affect the evolution of structure formation.


title:
Neutrino Degeneracy and Decoupling: New Limits from Primordial
  Nucleosynthesis and the Cosmic Microwave Background

abstract:
  We reanalyze the cosmological constraints on the existence of a net universal
lepton asymmetry and neutrino degeneracy. We show that neutrinos can begin to
decouple at higher temperatures than previous estimates due to several
corrections which diminish the neutrino reaction rate. These decoupled
neutrinos are therefore not heated as the particle degrees of freedom change.
The resultant ratio of the relic neutrino-to-photon temperatures after $e^\pm$
annihilation can then be significantly reduced by more than a factor of two
from that of the standard nondegenerate ratio. This changes the expansion rate
and subsequent primordial nucleosynthesis, photon decoupling, and structure
formation. In particular we analyze physically plausible lepton-asymmetric
models with large $\nu_\mu$ and $\nu_\tau$ degeneracies together with a
moderate $\nu_e$ degeneracy. We show that the nucleosynthesis by itself permits
very large neutrino degeneracies $0 \le \xinum$, $\xinut \le 40$, $0 \le \xinue
\le 1.4$ together with large baryon densities $0.1 \le \Omega_b \h502 \le 1$ as
long as some destruction of primordial lithium has occurred. We also show that
structure formation and the power spectrum of the cosmic microwave background
allows for the possibility of an $\Omega = 1$, $\Omega_\Lambda = 0.4$,
cosmological model for which there is both significant lepton asymmetry ($|
\xinum | = | \xinut | \approx 11$) and a relatively large baryon density
($\Omega_b \h502 \approx 0.2$). Our best-fit neutrino-degenerate,
high-baryon-content models are mainly distinguished by a suppression of the
second peak in the microwave background power spectrum. This is consistent with
the recent high resolution data from BOOMERANG and MAXIMA-1.


title:
Multi-wavelength Observations of Galaxies in the Southern Zone of
  Avoidance

abstract:
  We discuss the possibilities of extragalactic large-scale studies behind the
Zone of Avoidance (ZOA) using complementary multi-wavelength data from optical,
systematic blind HI, and near-infrared (NIR) surveys. Applying these data to
the NIR Tully-Fisher relation permits the mapping of the peculiar velocity
field across the ZOA. Here, we present results of a comparison of galaxies
identified in the rich low-latitude cluster Abell 3627 in the B-band with NIR
(DENIS) data, and cross-identifications of galaxies detected with the blind
Parkes HI Multibeam survey with NIR data - many of which are optically
invisible.


title:
The Enrichment History of the Intergalactic Medium: Measuring the CIV/HI
  Ratio in the Lyman Alpha Forest

abstract:
  We have obtained an exceptionally high S/N, high resolution spectrum of the
gravitationally lensed quasar Q1422+231 in order to investigate the metal
enrichment of the IGM. A column density distribution function (CDDF) is
determined for CIV, which is well fit by a power law with index 1.44 +/- 0.05.
Once a correction for incompleteness is applied, we find that the CDDF is
consistent with a power law down to log N(CIV) = 11.75, a factor of 10 more
sensitive than previously determined. In order to determine whether the CIV
enrichment extends to even lower column density HI clouds, we find that an
analysis of individual pixel optical depths is more robust than the stacking
technique. The results obtained from this optical depth method are compared
with analyses of simulated spectra enriched with varying CIV enrichment
recipes. From these simulations, we conclude that more CIV than is currently
directly detected in Q1422+231 is required to reproduce the optical depths
determined from the data, consistent with the conclusions drawn from
consideration of the power law distribution. (Abridged)


title: High Energy Physics and Quintessence

abstract:
  It is shown that any realistic model of quintessence should be based on
Supergravity (SUGRA) since the value of the quintessence field on the attractor
is approximately the Planck mass. Under very general assumptions, the typical
shape of a SUGRA tracking potential is derived. Cosmological implications are
investigated. In particular, it is demonstrated that, generically, the equation
of state parameter is driven to a value close to -1 in agreement with recent
observations.


title: ENEAR Redshift-Distance Survey: Cosmological Constraints

abstract:
  We present an analysis of the ENEAR sample of peculiar velocities of
elliptical galaxies, obtained with D_n-\sigma distances. We use the velocity
correlation function to analyze the statistics of the field-object's
velocities, while the analysis of the cluster data is based on the estimate of
their rms peculiar velocity, Vrms. The statistics of the model velocity field
is parameterized by the amplitude, \eta_8=\sigma_8 \Omega_m^{0.6}, and by the
shape parameter, \Gamma. From the velocity correlation statistics we obtain
\eta_8=0.51{-0.09}{+0.24} for \Gamma=0.25 at the 2\sigma level. Even though
less constraining, a consistent result is obtained by comparing the measured
Vrms of clusters to linear theory predictions. For \Gamma=0.25 we find
\eta_8=0.63{-0.19}{+0.22}$ at 1\sigma. Overall, our results point toward a
statistical concordance of the cosmic flows traced by spirals and early-type
galaxies, with galaxy distances estimated using TF and D_n-\sigma distance
indicators, respectively.


title: Planet formation is unlikely in equal mass binary systems with a ~ 50 AU

abstract:
  We show that planet formation via both gravitational collapse and core
accretion is unlikely to occur in equal mass binary systems with moderate (~ 50
AU) semi-major axes. Internal thermal energy generation in the disks is
sufficient to heat the gas everywhere so that spiral structures quickly decay
rather than grow or fragment. This same heating will inhibit dust coagulation
because the temperatures rise above the vaporization temperatures of many
volatile materials. We consider other processes not included in the model and
conclude that our temperatures are conservatively estimated (low), i.e. planet
formation is less likely in real systems than in the model.


title:
Overabundance of Calcium in the young SNR RX J0852$-$4622: evidence of
  over-production of $^{44}$Ti

abstract:
  Recently, COMPTEL has detected $\gamma$-rays of 1157 keV from $^{44}$Ti in
the direction of the SNR RX J0852$-$4622 (Iyudin et al. 1998). Since $^{44}$Ti
is a product of explosive nucleosynthesis and its half lifetime $\tau\sb{1/2}$
is about 60 yrs, RX J0852$-$4622 must be a young supernova remnant and
radiation is dominated by the ejecta rather than by interstellar matter. We
have detected an X-ray emission line at $4.1\pm 0.2$ keV which is thought to
come from highly ionized Ca. The emission line is so far only seen in the
north-west shell region of RX J0852$-$4622. The X-ray spectrum can be well
fitted with that of thin hot plasma of cosmic abundances except that of Ca,
which is overabundant by a factor of $8 \pm 5$. Assuming that most of Ca is
$^{44}$Ca, which originates from $^{44}$Ti by radioactive decay, we estimate a
total Ca mass of about $1.1\times 10^{-3}M_\odot$. Combining the amount of
$^{44}$Ca and the observed flux of the $^{44}$Ti $\gamma$-ray line, the age of
RX J0852$-$4622 is around 1000 yrs.


title: Discovery of 1RXS J171824.2-402934 as an X-ray burster

abstract:
  We report the first-time detection of a type-I X-ray burst from a position
that is consistent with that of 1RXS J171824.2-402934. The detection was made
on Sep 23, 1996, with the Wide Field Cameras on board the BeppoSAX satellite.
The burst had a peak intensity of 1.3 Crab units in 2 to 28 keV and is
relatively long (at least 3.5 min). Analysis of the burst gives clear evidence
for photospheric radius expansion. Assuming the peak luminosity to be close to
the Eddington limit, standard burst parameters and taking into account
gravitational redshift effects, the distance to the source is approximately 6.5
kpc. No other bursts from this source have been observed during the rest of the
WFC observations. The detection of a type-I burst implies that 1RXS
J171824.2-402934in all likelihood is a low-mass X-ray binary where the compact
object is a neutron star.


title: Disc heating in NGC 2985

abstract:
  Various processes have been proposed to explain how galaxy discs acquire
their thickness. A simple diagnostic for ascertaining this ``heating''
mechanism is provided by the ratio of the vertical to radial velocity
dispersion components. In a previous paper we have developed a technique for
measuring this ratio, and demonstrated its viability on the Sb system NGC 488.
Here we present follow-up observations of the morphologically similar Sab
galaxy NGC 2985, still only the second galaxy for which this ratio has been
determined outside of the solar neighbourhood. The result is consistent with
simple disc heating models which predict ratios of $\sigma_z / \sigma_R$ less
than one


title: Modeling a high mass turn down in the stellar initial mass function

abstract:
  Statistical sampling from the stellar initial mass function (IMF) for all
star-forming regions in the Galaxy would lead to the prediction of ~1000 Msun
stars unless there is a rapid turn-down in the IMF beyond several hundred solar
masses. Such a turndown is not necessary for dense clusters because the number
of stars sampled is always too small. Here we explore several mechanisms for an
upper mass cutoff, including an exponential decline of the star formation
probability after a turbulent crossing time. The results are in good agreement
with the observed IMF over the entire stellar mass range, and they give a
gradual turn down compared to the Salpeter function above ~100 Msun for normal
thermal Jeans mass, M_J. The upper mass turn down should scale with M_J in
different environments. A problem with the models is that they cannot give both
the observed power-law IMF out to the high-mass sampling limit in dense
clusters, as well as the observed lack of supermassive stars in whole galaxy
disks. Either there is a sharper upper-mass cutoff in the IMF, perhaps from
self-limitation, or the IMF is different for dense clusters than for the
majority of star formation that occurs at lower density. Dense clusters seem to
have an overabundance of massive stars relative to the average IMF in a galaxy.


title: 28SiO, 29SiO and 30SiO excitation: effects of infrared line overlaps

abstract:
  We have investigated the influence of several line overlaps between 28SiO,
29SiO and 30SiO on maser emission from the envelopes of late-type stars using
the Large Velocity Gradient radiative transfer formalism modified to account
for overlaps. Our model includes: (i) 40 rotational levels for each of the v=0
to 4 vibrational states and each isotopic species; (ii) collisions with
molecular and atomic hydrogen; and (iii) radiative pumping by a shell of dust
grains surrounding the SiO masing layers.
  We have shown that several line overlaps may play a role on the excitation of
the 28SiO v=3, J=1-0 maser, and on the anomalously weak v=3, J=2-1 emission. We
suggest that 28SiO maser emission in the v=4, J=5-4 line, the only one observed
in this vibrational level, may also result from line overlaps. For 29SiO,
infrared line overlaps successfully explain observed maser emission in the v=0,
J=5-4 and v=1, 2, J=6-5 lines. 30SiO, v=0, J=2-1, and v=0, J=4-3 maser
emissions could also result from line overlaps, and we find that several
overlaps could explain the newly discovered maser line 30SiO v=1, J=1-0.
Finally, we make some predictions for new 28SiO, 29SiO and 30SiO maser lines.


title:
Formation of binary millisecond pulsars with relatively high surface
  dipole magnetic fields

abstract:
  We have carried out numerical evolutionary calculations of binary systems to
investigate the formation of binary millisecond pulsars (pulsars with white
dwarf companions). We apply the ``standard scenario'' in which the binary
pulsars are formed from low-mass and intermediate-mass X-ray binaries as well
the alternative scenario in which the neutron stars are formed by
accretion-induced collapse (AIC) of white dwarfs. The mass transfer processes
are carefully followed by taking into account a number of binary interactions.
Assuming that the magnetic fields of the neutron stars decay due to the
accretion, we calculate the pulsar surface dipole magnetic field strength at
the end of the mass transfer as a function of the final orbital period. We find
that while the observed data of the majority of pulsars are compatible with the
derived relations, we fail to produce binary pulsars with relatively high
magnetic fields and short orbital periods (such as PSR B0655+64). We conclude
that those systems are most likely formed through common-envelope phase.


title: Inertial Instability of Accretion Disks with Relativistic Electrons

abstract:
  We show that accretion disks with relativisticly hot electrons which are
coupled to cold ions is subject to inertial-type instability in which kinematic
drag between electrons and ions produces radial acceleration of electrons.


title: FUSE Observations of Interstellar Gas Towards the LMC Star Sk -67 05

abstract:
  We report on measurements of interstellar O VI, H2, P II, Si II, Ar I, and Fe
II absorption along the line of sight to Sk -67 05, a B0 Ia star in a diffuse H
II region in the western edge of the Large Magellanic Cloud (LMC). We find log
N(O VI) = 14.40 +/- 0.04 in the Milky Way (MW) component and, using the C IV
column density from previous IUE observations, N(C IV) / N(O VI) = 1.00 +/-
0.16, a value similar to other halo measurements made with FUSE. In the LMC
component, log N(O VI) = 13.89 +/- 0.05, and N(C IV) / N(O VI) < 0.4 (3 sigma),
since only an upper limit on N(C IV) is available. Along this sightline the LMC
is rich in molecular hydrogen, log N(H2) = 19.50 +/- 0.08; in the MW log N(H2)
= 14.95 +/- 0.08. A two-component fit for the excitation temperature of the
molecular gas in the LMC gives T_01 = 59 +/- 5 K for J=0,1 and T_ex = 800 +/-
330 K for J=3,4,5. For the MW, T_01 = 99 (+30/-20) K; no excitation temperature
could be determined for the higher rotational states. The MW and LMC gas-phase
[Fe/P] abundances are ~0.6 and ~0.7 dex lower, respectively, than solar system
abundances. These values are similar to [Fe/Zn] measurements for the MW and LMC
towards SN 1987A.


title:
Periodic modulation of the optical counterpart of the X-ray pulsator
  1WGA J1958.2+3232. A new intermediate polar

abstract:
  Time-resolved observations of a 6' x 6' field, containing the position error
boxes of the X-ray source 1WGA J1958.2+3232, were performed in June 1999 with
the 91 cm Catania telescope, equipped with a Photon Counting Intensified CCD.
The star recently proposed as the optical counterpart of the 1WGA J1958.2+3232,
exhibited a strong optical modulation with a period compatible with that seen
in X-ray (~12 min). The optical modulation was detected again in September and
October 1999. These results confirm the identification of the optical
counterpart and support the classification of 1WGA J1958.2+3232 as a
cataclysmic variable, possibly an Intermediate Polar. Modulation at period
twice as large was also found in one observation run, suggesting that the true
spin period of the White Dwarf could be 24 min rather than 12 min, thus 1WGA
J1958.2+3232 appears to be, among the IPs, the slowest rotator which exhibit
double peaked spin profile.


title: Detecting the First Objects in the Mid-IR with NGST

abstract:
  We calculate the expected Mid-IR molecular hydrogen line emission from the
first objects in the universe. Due to their low masses, the stellar feedback
from massive stars is able to blowaway their gas content and collect it into a
cooling shell where H_2 rapidly forms and IR roto-vibrational (as for example
the restframe 2.12 micron) lines carry away a large fraction (up to 10%) of the
explosion energy. The fluxes from these sources are in the range
10^{-21}-10^{-17} erg/s/cm^2. The highest number counts are expected in the 20
micron band, where about 10^5 sources/deg^2 are predicted at the limiting flux
of 3 \times 10^{-18} erg/s/cm^2. Among the planned observational facilities, we
find that the best detection perspectives are offered by NGST, which should be
able to reveal about 200 first objects in one hour observation time at its
limiting flux in the above band. Therefore, Mid-IR instruments appear to
represent perfect tools to trace star formation and stellar feedback in the
high (z>5) redshift universe.


title:
X-ray Astronomy with CCDs: Calibration of the Advanced CCD Imaging
  Spectrometer and Observations of Rotation-powered Pulsars

abstract:
  (ABRIDGED)
  This dissertation concerns the use of CCDs for for X-ray astronomy. Part I of
this thesis focuses on the calibration of the Advanced CCD Imaging Spectrometer
(ACIS), one of the two primary focal plane instruments on the Chandra X-ray
Observatory. I begin by presenting a series of measurements made using
undispersed synchrotron radiation. I analyzed the results of these experiments
to extract parameters necessary to model the absolute detection efficiency of
CCDs used as reference standards for ACIS characterization. I also discuss a
novel "mesh" technique I pioneered to non-destructively measure the sub-pixel
structure of CCDs, including the channel stops and gates. Guided by the results
of the mesh experiments, I performed additional measurements to constrain
recombination effects in the channel stops.
  Part II of this thesis concerns the X-ray properties of rotation- powered
(radio) pulsars. High energy observations serve as a powerful diagnostic of the
energetics and emission mechanisms of neutron stars. I analyze ASCA and ROSAT
observations of three young pulsars which are particularly well-suited for
addressing these issues. I also present observations of the rotation-powered
pulsar with the highest known magnetic field, and describe how the results
relate to anomalous X-ray pulsars, another type of neutron star. Finally, I
analyze Chandra observations of the supernova remnant Cas A. These data fully
demonstrate the capabilities of ACIS and reveal a previously unknown point
source at the center of the remnant.


title:
HST/STIS spectroscopy of the optical outflow from DG Tau: structure and
  kinematics on sub-arcsecond scales

abstract:
  We have carried out a spatio-kinematic study of the outflow from the
classical T Tauri star DG Tau using the Space Telescope Imaging Spectrograph
(STIS) on board the Hubble Space Telescope (HST). A series of seven spatially
offset long-slit spectra spaced by 0.07'' were obtained along the axis of the
outflow to build up a 3-D intensity-velocity ``cube'' in various forbidden
emission lines (FELs) and Ha. Here we present high spatial resolution synthetic
line images close to the star in distinct radial velocity intervals (from ~ +50
km/s to ~ -450 km/s in four bins, each ~ 125 km/s wide). The lowest velocity
emission is also examined in finer detail (from +60 km/s to -70 km/s in five
bins ~ 25 km/s wide). We have found that the highest velocity and most highly
collimated component, i.e. the jet, can be traced from DG Tau to a distance D ~
0.7''. The jet is on the axis of a pear-shaped limb-brightened bubble which
extends between 0.4'' and 1.5'' from the source and which we interpret as a bow
shock. Other condensations are seen close to the star indicating ongoing
temporal variations in the flow. The low-velocity component of the outflow is
found to be spatially wide close to the source (~ 0.2'' at D=0.2''), in
contrast to the high velocity jet (width <~ 0.1''). We have also found evidence
to suggest that the density increases longitudinally with proximity to the
source and also laterally towards the flow axis. Thus, at least in the case of
DG Tau, the flow becomes gradually denser as it increases in velocity and
becomes more collimated. Our observations show a continous bracketing of the
higher speed central flow within the lower speed, less collimated, broader
flow, down to the lowest velocity scales. This suggests that the low and high
velocity FELs in the highly active T Tauri star DG Tau are intimately related.


title:
Magnetorotational Instability in Protoplanetary Disks. II. Ionization
  State and Unstable Regions

abstract:
  We investigate where in protoplanetary disks magnetorotational instability
operates, which can cause angular momentum transport in the disks. We
investigate the spatial distribution of various charged particles and the
unstable regions for a variety of models for protoplanetary disks taking into
account the recombination of ions and electrons at grain surfaces, which is an
important process in most parts of the disks. We find that for all the models
there is an inner region which is magnetorotationally stable due to ohmic
dissipation. This must make the accretion onto the central star non-steady. For
the model of the minimum-mass solar nebula, the critical radius, inside of
which the disk is stable, is about 20 AU, and the mass accretion rate just
outside the critical radius is 10^{-7} - 10^{-6} M_{\odot} yr^{-1}. The stable
region is smaller in a disk of lower column density. Dust grains in
protoplanetary disks may grow by mutual sticking and may sediment toward the
midplane of the disks. We find that the stable region shrinks as the grain size
increases or the sedimentation proceeds. Therefore in the late evolutionary
stages, protoplanetary disks can be magnetorotationally unstable even in the
inner regions.


title: A Jet Model for the Afterglow Emission from GRB000301C

abstract:
  We present broad-band radio observations of the afterglow of GRB000301C,
spanning from 1.4 to 350 GHz for the period of 3 to 83 days after the burst.
This radio data, in addition to measurements at the optical bands, suggest that
the afterglow arises from a collimated outflow, i.e. a jet. To test this
hypothesis in a self-consistent manner, we employ a global fit and find that a
model of a jet, expanding into a constant density medium (ISM+jet), provides
the best fit to the data. A model of the burst occurring in a wind-shaped
circumburst medium (wind-only model) can be ruled out, and a wind+jet model
provides a much poorer fit of the optical/IR data than the ISM+jet model. In
addition, we present the first clear indication that the reported fluctuations
in the optical/IR are achromatic with similar amplitudes in all bands, and
possibly extend into the radio regime. Using the parameters derived from the
global fit, in particular a jet break time, t_{jet}=7.5 days, we infer a jet
opening angle of \theta=0.2, and consequently the estimate of the emitted
energy in the GRB itself is reduced by a factor of 50 relative to the isotropic
value, giving E=1.1 \times 10^{51} ergs.


title: Galactic Bulge Microlensing Events with Clump Giants as Sources

abstract:
  We present preliminary results of the analysis of 5 years of MACHO data on
the Galactic bulge microlensing events with clump giants as sources. In
particular, we discuss: 1) the selection of `giant' events, 2) distribution of
impact parameters, 3) distribution of event durations, 4) the concentration of
long duration events in MACHO field 104 centered on (l,b) = (3.1,-3.0). We
report the preliminary average optical depth of (2.0 +/- 0.4) x 10^{-6}
(internal) at (l,b) = (3.9,-3.8). We discuss future work and prospects for
building a coherent model of the Galaxy.


title: Hard X-ray Observation of Abell 496

abstract:
  We report the results of hard X-ray observations of Abell 496 (A496), a
nearby relaxed cluster, using the Rossi X-ray Timing Explorer (RXTE). The 3-20
keV spectrum of this cluster is well-modeled by a thermal component of kT ~ 4.1
keV plus a cooling flow with mass accretion rate of \dot{M} ~ 285 M_{\odot}
yr^{-1}. The spectrum is equally well-modeled by a multi-temperature plasma
component with a Gaussian temperature distribution of mean temperature 3.8 keV
and \sigma_{kT} ~ 0.9 keV. The metallicity is found to be approximately 1/3
solar; however, the Ni/Fe ratio is about 3.6. No significant nonthermal
emission at hard X-rays was detected for this cluster. We discuss the
implications of the models presented here and compare them with the temperature
profiles derived for this cluster using the Advanced Satellite for Cosmology
and Astrophysics (ASCA). Our results are inconsistent with declining
temperature profiles.


title:
A New Analysis Method for Reconstructing the Arrival Direction of TeV
  Gamma-rays Using a Single Imaging Atmospheric Cherenkov Telescope

abstract:
  We present a method of atmospheric Cherenkov imaging which reconstructs the
unique arrival direction of TeV gamma rays using a single telescope. The method
is derived empirically and utilizes several features of gamma-ray induced air
showers which determine, to a precision of 0.12 degrees, the arrival direction
of photons, on an event-by-event basis. Data from the Whipple Observatory's 10
m gamma-ray telescope is utilized to test selection methods based on source
location. The results compare these selection methods with traditional
techniques and three different camera fields of view. The method will be
discussed in the context of a search for a gamma-ray signal from a point source
located anywhere within the field of view and from regions of extended
emission.


title: Maximum Entropy Reconstruction of the Interstellar Medium: I. Theory

abstract:
  We have developed a technique to map the three-dimensional structure of the
local interstellar medium using a maximum entropy reconstruction technique. A
set of column densities N to stars of known distance can in principle be used
to recover a three-dimensional density field n, since the two quantities are
related by simple geometry through the equation N = C n, where C is a matrix
characterizing the stellar spatial distribution. In practice, however, there is
an infinte number of solutions to this equation. We use a maximum entropy
reconstruction algorithm to find the density field containing the least
information which is consistent with the observations. The solution obtained
with this technique is, in some sense, the model containing the minimum
structure. We apply the algorithm to several simulated data sets to demonstrate
its feasibility and success at recovering ``real'' density contrasts.
  This technique can be applied to any set of column densities whose end points
are specified. In a subsequent paper we shall describe the application of this
method to a set of stellar color excesses to derive a map of the dust
distribution, and to soft X-ray absorption columns to hot stars to derive a map
of the total density of the interstellar medium.


title: Intrinsic and Extrinsic Galaxy Alignment

abstract:
  We show with analytic models that the assumption of uncorrelated intrinsic
ellipticities of target sources that is usually made in searches for weak
gravitational lensing due to large-scale mass inhomogeneities (``field
lensing'') is unwarranted. If the orientation of the galaxy image is determined
either by the angular momentum or the shape of the halo in which it forms, then
the image should be aligned preferentially with the component of the tidal
gravitational field perpendicular to the line of sight. Long-range correlations
in the tidal field will thus lead to long-range ellipticity-ellipticity
correlations that mimic the shear correlations due to weak gravitational
lensing. We calculate the ellipticity-ellipticity correlation expected if halo
shapes determine the observed galaxy shape, and we discuss uncertainties (which
are still considerable) in the predicted amplitude of this correlation. The
ellipticity-ellipticity correlation induced by angular momenta should be
smaller. We consider several methods for discriminating between the
weak-lensing (extrinsic) and intrinsic correlations, including the use of
redshift information. An ellipticity--tidal-field correlation also implies the
existence of an alignment of images of galaxies near clusters. Although the
intrinsic alignment may complicate the interpretation of field-lensing results,
it is inherently interesting as it may shed light on galaxy formation as well
as on structure formation.


title:
On the Perils of Hyperfine Splitting: A reanalysis of Mn and Sc
  Abundance Trends

abstract:
  We investigate the impact of hyperfine splitting on stellar abundance
analyses of Mn and Sc, and find that incorrect hfs treatment can lead to
spurious abundance trends with metallicity. We estimate corrections to a recent
study by Nissen et al. (2000), and find: (1) [Mn/Fe] is described by a bimodal
distribution, with [Mn/Fe] ~ -0.3 for stars [Fe/H] < -0.7, and [Mn/Fe] ~ -0.05
for stars at higher metallicity, suggestive of a transition between halo/thick
disk and thin disk populations. (2) The large majority of stars show nearly
solar [Sc/Fe] ratios; although important deviations cannot be ruled-out.


title: Rapid Optical Followup Observations of SGR Events with ROTSE-I

abstract:
  In order to observe nearly simultaneous emission from Gamma-ray Bursts
(GRBs), the Robotic Optical Transient Search Experiment (ROTSE) receives
triggers via the GRB Coordinates Network (GCN). Since beginning operations in
March, 1998, ROTSE has also taken useful data for 10 SGR events: 8 from SGR
1900+14 and 2 from SGR 1806-20. We have searched for new or variable sources in
the error regions of these SGRs and no optical counterparts were observed.
Limits are in the range m_ROTSE ~ 12.5 - 15.5 during the period 20 seconds to 1
hour after the observed SGR events.


title:
Evidence for tidal interaction and a supergiant HI shell in the Local
  Group dwarf galaxy NGC 6822

abstract:
  We present a wide-field, high spatial and velocity resolution map of the
entire extended HI distribution of the Local Group dwarf galaxy NGC 6822. The
observations were obtained with the Australia Telescope Compact Array in
mosaicing mode. The interstellar medium of NGC 6822 is shaped by the presence
of numerous H{\sc i} holes and shells, including a supergiant shell, and the
effects of tidal interaction, in the form of a tidal arm and an infalling or
interacting HI complex. The HI shell is situated outside the optical galaxy and
occupies roughly a quarter of the area of the main HI disk. It measures 2.0
times 1.4 kpc, making it one of the largest supergiant HI shells ever found.
The giant hole shows no signs of expansion and no obvious creation mechanism is
evident from our data. If star formation was the cause, an energy equivalent of
\~100 supernovae (10^53 erg) is needed to create the hole. We derive an upper
limit for the age of order 100 Myr. The presence of a possible tidal arm
indicates that NGC 6822 may recently have undergone some interaction. An HI
complex located in the north-west of the galaxy may be the interaction partner.
We argue that it is likely that these features were created about 100 Myr ago
in an event that also enhanced the star formation rate


title:
Electrodynamic Structure of Outer Gap Accelerators: Invisibility of
  Pulsed Tev Fluxes

abstract:
  We study the structure of an outer-magnetospheric gap around a rotating
neutron star. Migratory electrons and positrons are accelerated by the electric
field exerted in the gap and radiate copious gamma-rays via curvature process.
Some of the gamma-rays materialize by colliding with the X-rays illuminating
the gap, leading to a pair production cascade. The replenished charges
partially screen the original acceleration field, which is self-consistently
solved from the Poisson equation, together with the Boltzmann equations for
gamma-rays and the continuity equations for particles. We demonstrate that it
is difficult to detect the TeV emission due to Compton upscatterings in the
gap, by the current ground-based telescopes.


title: Limits on Neutrino Masses from Large-Scale Structure

abstract:
  Massive neutrinos have a detectable effect on cosmological structure
formation, in particular on the large-scale distribution of galaxies. Adding
Hot Dark Matter to the now-standard Lambda CDM model leads to a worse fit to
large-scale structure and CMB anisotropy data. This results in a limit on the
mass of the most massive neutrino of 4 eV, assuming a power-law primordial
power spectrum.


title:
Is the Lambda CDM Model Consistent with Observations of Large-Scale
  Structure?

abstract:
  The claim that large-scale structure data independently prefers the Lambda
Cold Dark Matter model is a myth. However, an updated compilation of
large-scale structure observations cannot rule out Lambda CDM at 95%
confidence. We explore the possibility of improving the model by adding Hot
Dark Matter but the fit becomes worse; this allows us to set limits on the
neutrino mass.


title:
X-ray observations of supernova remnant G54.1+0.3: X-ray spectrum and
  the discovery of an X-ray jet

abstract:
  We present in this paper analyses of the $ROSAT$ PSPC and $ASCA$ SIS and GIS
observations of the Crab-like supernova remnant (SNR) G54.1+0.3. Its spectrum
obtained by $ROSAT$ PSPC favors a power law model with a photon index of
-0.8$^{+0.8}_{-2.0}$, absorbed energy flux in 0.1-2.4 keV of 1.0$\times
10^{-12}$ erg cm$^{-2}$ s$^{-1}$, and absorption column density of
12.3$^{+8.0}_{-3.2}\times 10^{21}$ cm$^{-2}$. $ASCA$ SIS observation shows that
its spectrum can also be best fitted with power law model. The fitted
parameters are, photon index -1.9$^{+0.1}_{-0.2}$, absorbed energy flux in
0.7-2.1 keV 6.5$\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$, and column density
17.9$^{+2.8}_{-2.5}\times 10^{21}$ cm$^{-2}$. The high absorption column
density indicates a distance similar to the radius of the galaxy. The 0.1-2.4
keV X-ray luminosity of G54.1+0.3 is 3.2$\times10^{33}$$d_{10}^2$ erg s$^{-1}$,
where $d_{10}$ is the distance in 10 kpc. With an image restoration method we
have obtained high spatial resolution X-ray image of the remnant, which clearly
shows an X-ray jet pointing to the northeast with a length about 40$\arcsec$
from the center of the nebula. Its X-ray luminosity in 0.1-2.4 keV is about
5.1$\times10^{32}$$d_{10}^2$ erg s$^{-1}$. The X-ray jet is consistent with the
radio extension to the northeast in both direction and position. We propose
that the X-ray jet is connected with the pulsar assumed to exist in the
remnant.


title:
Implications of a possible 23 day periodicity for binary black hole
  models in Mkn~501

abstract:
  We investigate the implications of a massive binary system in the centre of
the gamma-ray blazar Mkn~501 and show that the periodical behaviour recently
observed in the TeV and X-ray lightcurves may possibly be related to the
orbital motion of the relativistic jet emerging from the less massive black
hole. For the special relativistic jet properties inferred from emission
models, we derive an intrinsic orbital period of $(6-14)$ yrs and a
centre-of-mass distance of $(2.0-3.5) \times 10^{16}$ cm. If the binary is very
close with a separation of the order of that for which gravitational radiation
becomes dominant, we find a maximum primary mass of $\sim 10^8 M_{\sun}$ and a
corresponding secondary mass in the range of $\sim (4-42)\times 10^6 M_{\sun}$
depending on the intrinsic jet properties. Such values are in line with the
black hole masses expected from merger scenarios.


title: On the nonthermal X-ray emission in blazar jets

abstract:
  We consider particle acceleration to high energy via diffusive shock
acceleration in a simple, self-consistent shock in jet model for blazars.
Electrons are assumed to be accelerated at a shock front in relativistic jets
and radiate synchrotron emission in a post-shock region. The full time, space
and momentum dependence of the electron distribution function is used for a
calculation of the nonthermal synchrotron spectra. We discuss the evolution of
the spectral index by varying the rate at which particles enter the
acceleration process. The results indicate that the synchrotron spectral index
displays a characteristic looplike behaviour with intensity (as has been
observed in several blazars), where the orientation of the loop depends on
whether the acceleration time scale is comparable to the synchrotron cooling
time scale or not. We show that our model provides a good fit to the observed
evolution of the spectral index of Mkn 421 during a flare in 1994.


title: Irradiation and mass transfer in low-mass compact binaries

abstract:
  We study the reaction of low-mass stars to anisotropic irradiation and its
importance for the long-term evolution of compact binaries binaries. We show by
means of a simple homology model that if the energy outflow through the surface
layers of a low-mass main sequence star is blocked over a fraction s_eff < 1 of
its surface it will inflate only modestly and that the maximum contribution to
mass transfer is s_eff times what one obtains in the isotropic case. The
duration of this mass transfer phase is roughly -0.1 ln(1-s_eff) times the
thermal time scale of the convective envelope. Numerical computations confirm
these results. Second, we present a simple analytic one-zone model for
computing the blocking effect by irradiation which gives results in acceptable
quantitative agreement with detailed numerical computations. Third, we show
that unless mass transfer is strongly enhanced by consequential angular
momentum losses, cataclysmic variables are stable against mass transfer if the
mass of the main sequence donor is less than about 0.7 solar masses. Otherwise
systems may be unstable, subject to the efficiency of irradiation. We argue
that low-mass X-ray binaries are even less susceptible to this instability. In
case of instability, mass transfer must evolve through a limit cycle in which
phases of high mass transfer alternate with phases of small (or no) mass
transfer.


title: The Connection between Globular Cluster Systems and the Host Galaxies

abstract:
  A large number of early type galaxies are now known to possess blue and red
subpopulations of globular clusters. We have compiled a database of 28 such
galaxies exhibiting bimodal globular cluster colour distributions. After
converting to a common V-I colour system, we investigate correlations between
the mean colour of the blue and red subpopulations with galaxy velocity
dispersion. We support previous claims that the mean colour of the blue
globular clusters are unrelated to their host galaxy. They must have formed
rather independently of the galaxy potential they now inhabit. The mean blue
colour is similar to that for halo globular clusters in our Galaxy and M31. The
red globular clusters, on the other hand, reveal a strong correlation with
galaxy velocity dispersion. Futhermore, in well-studied galaxies the red
subpopulation has similar, and possibly identical, colours to the galaxy halo
stars. Our results indicate an intimate link between the red globular clusters
and the host galaxy; they share a common formation history. A natural
explanation for these trends would be the formation of the red globular
clusters during galaxy collapse.


title:
Probing the gas content of the dwarf galaxy NGC 3109 with background
  X-ray sources

abstract:
  We established the catalog of X-ray point sources in the field of the
Magellanic-type spiral galaxy NGC 3109 (DDO 236) from two ROSAT PSPC
observations. Of the 91 X-ray sources 26 are contained within the HI extent of
NGC 3109 as derived by Jobin & Carignan (1990) with the VLA. For 10 of these we
can determine accurate hardness ratios delta HR2<=0.2. We find 3 candidate AGN,
2 candidate X-ray binaries and one source which may belong to either class. We
also find 2 candidate foreground stars. In a field of 8'x8' observed with the
NTT in the I-band and centered on the nucleus of NGC 3109 we determine
candidate optical counterparts in the X-ray error circle of 7 ROSAT PSPC
sources. We apply a spectral fit to the ROSAT spectrum of the X-ray brightest
absorbed candidate AGN behind NGC 3109, RX J1003.2-2607. Assuming a galactic
foreground hydrogen column density of 4.3 10^20 cm^-2 we derive from the X-ray
spectral fit, assuming reduced metallicities (~0.2 solar), a hydrogen column
density due to NGC 3109 of 11(+7,-5) 10^20 cm^-2. This value is slightly larger
than the hydrogen column density derived from the 21-cm observations of ~8
10^20 cm^-2. We estimate that the molecular mass fraction of the gas is not
larger than ~60%.