title: Nonthermal Emission from a Supernova Remnant in a Molecular Cloud

abstract:
  In evolved supernova remnants (SNRs) interacting with molecular clouds, such
as IC 443, W44, and 3C391, a highly inhomogeneous structure consisting of a
forward shock of moderate Mach number, a cooling layer, a dense radiative shell
and an interior region filled with hot tenuous plasma is expected. We present a
kinetic model of nonthermal electron injection, acceleration and propagation in
that environment and find that these SNRs are efficient electron accelerators
and sources of hard X- and gamma-ray emission. The energy spectrum of the
nonthermal electrons is shaped by the joint action of first and second order
Fermi acceleration in a turbulent plasma with substantial Coulomb losses.
Bremsstrahlung, synchrotron, and inverse Compton radiation of the nonthermal
electrons produce multiwavelength photon spectra in quantitative agreement with
the radio and the hard emission observed by ASCA and EGRET from IC 443. We
distinguish interclump shock wave emission from molecular clump shock wave
emission accounting for a complex structure of molecular cloud. Spatially
resolved X- and gamma- ray spectra from the supernova remnants IC 443, W44, and
3C391 as might be observed with BeppoSAX, Chandra XRO, XMM, INTEGRAL and GLAST
would distinguish the contribution of the energetic lepton component to the
gamma-rays observed by EGRET.


title: Searching for periodicities in the MACHO light curve of LMC X-2

abstract:
  Using the exceptional long-term monitoring capabilities of the MACHO project,
we present here the optical history of LMC X-2 for a continuous 6-yr period.
These data were used to investigate the previously claimed periodicities for
this source of 8.15 h and 12.54 d : we find upper amplitude limits of 0.10 mag
and 0.09 mag, respectively.


title:
Erratum: ASCA Observations of the Absorption-Line Features from the
  Super-Luminal Jet Source GRS 1915+105

abstract:
  We have discovered errors in the calculation of some of the Einstein
coefficients in Table 5 and some plots in Figure 3. Due to the errors, the
square-root section of the curves of growth of Fe xxvi Ka and Kb, and Ni xxviii
Ka in Figure 3 were a few times underestimated. We correct Table 5 and re-plot
Figure 3 together with the unaffected curves. The program to calculate the
corrected curves of growth is available at
http://www.hp.phys.titech.ac.jp/kotani/cog/index.html


title: Knots in the outer shells of the planetary nebulae IC 2553 and NGC 5882

abstract:
  We present images and high-resolution spectra of the planetary nebulae IC
2553 and NGC 5882. Spatio-kinematic modeling of the nebulae shows that they are
composed of a markedly elongated inner shell, and of a less aspherical outer
shell expanding at a considerably higher velocity than the inner one. Embedded
in the outer shells of both nebulae are found several low-ionization knots. In
IC 2553, the knots show a point-symmetric distribution with respect to the
central star: one possible explanation for their formation is that they are the
survivors of pre-existing point-symmetric condensations in the AGB wind, a fact
which would imply a quite peculiar mass-loss geometry from the giant
progenitor. In the case of NGC 5882, the lack of symmetry in the distribution
of the observed low-ionization structures makes it possible that they are the
result of in situ instabilities.


title:
Gravitational potential energy of simple bodies: the method of negative
  density

abstract:
  The method of negative density is presented which allows to obtain the
analytical solutions for potential energy of new kinds of homogeneous and
ihhomogeneous self-gravitating bodies. The homogeneous bispherical
concavo-convex lens is considered in particular.


title:
Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD
  photometry

abstract:
  We report BV(RI)c CCD photometric data for a group of seven Cepheid variables
in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The
photometry was obtained as part of a program to determine accurate distances to
these Cepheids by means of the infrared surface brightness technique, and to
improve the LMC Cepheid database for constructing Cepheid PL and PLC relations.
Using the new data together with data from the literature, we have determined
improved periods for all variables. For five fundamental mode pulsators, the
light curves are now of excellent quality and will lead to accurate distance
and radius determinations once complete infrared light curves and radial
velocity curves for these variables become available.


title:
A 695-Hz quasi-periodic oscillation in the low-mass X-ray binary EXO
  0748-676

abstract:
  We report the discovery of a 695-Hz quasi-periodic oscillation (QPO) in data
taken with the Rossi X-ray Timing Explorer of the low-mass X-ray binary (LMXB)
EXO 0748-676. This makes EXO 0748-676 the second dipping LMXB, after 4U
1915-05, that shows kHz QPOs. Comparison with other sources suggests that the
QPO corresponds to the lower frequency peak of the kHz QPO pair often observed
in other LMXBs. The QPO was found in the only observation done during an
outburst of the source in early 1996. This observation is also the only one in
which the ~1 Hz QPO recently found in EXO 0748-676 is not present.


title: Supernovae versus Neutron Star Mergers as the Major r-Process Sources

abstract:
  I show that recent observations of r-process abundances in metal-poor stars
are difficult to explain if neutron star mergers (NSMs) are the major r-process
sources. In contrast, such observations and meteoritic data on Hf182 and I129
in the early solar system support a self-consistent picture of r-process
enrichment by supernovae (SNe). While further theoretical studies of r-process
production and enrichment are needed for both SNe and NSMs, I emphasize two
possible direct observational tests of the SN r-process model: gamma rays from
decay of r-process nuclei in SN remnants and surface contamination of the
companion by SN r-process ejecta in binaries.


title:
On the Disappearance of Kilohertz Quasi-Periodic Oscillations at a High
  Mass Accretion Rate in Low-Mass X-ray Binaries

abstract:
  For all sources in which the phenomenon of kilo-Hertz quasi-periodic
oscillation (kHz QPO) is observed, the QPOs disappear abruptly when the
inferred mass accretion rate exceeds a certain threshold. Although the
threshold cannot at present be accurately determined (or even quantified)
observationally, it is clearly higher for bright Z sources than for faint atoll
sources. Here we propose that the observational manifestation of kHz QPOs {\em
requires} direct interaction between the neutron star magnetosphere and the
Keplerian accretion disk and that the cessation of kHz QPOs at high accretion
rate is due to the lack of such an interact when the Keplerian disk terminates
at the last stable orbit and yet the magnetosphere is pushed farther inward.
The threshold is therefore dependent of the magnetic field strength -- the
stronger the magnetic field the higher the threshold. This is certainly in
agreement with the atoll/Z paradigm, but we argue that it is also generally
true, even for individual sources within each (atoll or Z) category. For atoll
sources, the kHz QPOs also seem to vanish at low accretion rate. Perhaps the
``disengagement'' between the magnetosphere and the Keplerian disk also takes
place under such circumstances, because of, for instance, the presence of
quasi-spherical advection-dominated accretion flow (ADAF) close to the neutron
star. Unfortunately, in this case, the estimation of the accretion rate
threshold would require a knowledge of the physical mechanisms that cause the
disengagement. If the ADAF is responsible, the threshold is likely dependent of
the magnetic field of the neutron star.


title: Lower Limit on Radius as a Function of Mass for Neutron Stars

abstract:
  While model-independent limits are always interesting, a limit on neutron
star radius as a function of mass attains special interest in light of recent
interpretations of the periodic as well as quasi-periodic oscillations (QPOs)
in brightness of X-rays emitted from neutron stars that are accreting matter
from a low-mass companion. Here we derive such a limit based only on well
accepted principles. We discuss our limit in connection with a recent
interpretation of X-ray pulsations from SAX J1808.4-3658 as indicating a
strange-star candidate, and show that this object can also be a normal neutron
star, though one whose central core has very high density. The most plausible
high-density phase of hadronic matter, which is also expected to be very
compressible, is quark matter. So an alternative to the strange star
interpretation of SAX J1808.4-3658 is that it is a hybrid neutron star.


title: HI Bright Galaxies in the Southern Zone of Avoidance

abstract:
  A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212
deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver
on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral
galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110
galaxies. Of these, 67 have no counterparts in the NASA/IPAC Extragalactic
Database. In general, the uncataloged galaxies lie behind thicker obscuration
than do the cataloged objects. All of the newly-discovered galaxies have HI
flux integrals more than an order of magnitude lower than the Circinus galaxy.
The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg &
Huchtmeier 1992), and the Local Void remains empty. The HI mass function
derived for the sample is satisfactorily fit by a Schechter function with
parameters alpha = 1.51 +- 0.12, Phi* = 0.006 +- 0.003, and log M* = 9.7 +-
0.10.


title:
Analytic Light-Curves of Gamma-Ray Burst Afterglows: Homogeneous versus
  Wind External Media

abstract:
  Assuming an adiabatic evolution of a Gamma-Ray Burst (GRB) remnant
interacting with an external medium, we calculate the injection, cooling, and
absorption break frequencies, and the afterglow flux for plausible orderings of
the break and observing frequencies. The analytical calculations are restricted
to a relativistic remnant and, in the case of collimated ejecta, to the phase
where there is an insignificant lateral expansion. Results are given for both a
homogeneous external medium and for a wind ejected by the GRB progenitor.
  We compare the afterglow emission at different observing frequencies, for
each type of external medium. It is found that observations at sub-millimeter
frequencies during the first day provide the best way of discriminating between
the two models. By taking into account the effect of inverse Compton
scatterings on the electron cooling, a new possible time-dependence of the
cooling break is identified. The signature of the up-scattering losses could be
seen in the optical synchrotron emission from a GRB remnant interacting with a
pre-ejected wind, as a temporary mild flattening of the afterglow decay. The
up-scattered radiation itself should be detected in the soft X-ray emission
from GRB remnants running into denser external media, starting few hours after
the main event.


title: UV Light Curves of Thermonuclear Supernovae

abstract:
  Ultraviolet light curves are calculated for several thermonuclear supernova
models using a multifrequency radiation hydrodynamic code. It is found that
Chandrasekhar-mass models produce very similar light curves both for detonation
and deflagration. Sub-Chandrasekhar-mass models essentially differ from
``normal'' Chandrasekhar ones regarding behaviour of their UV fluxes.
Differences in absolute brightness and in shape of light curves of
thermonuclear supernovae could be detectable up to 300 Mpc with modern UV space
telescopes.


title: The line of sight velocity distributions of simulated merger remnants

abstract:
  We use Gauss-Hermite functions to study the line of sight velocity
distributions in simulated merger remnants. Our sample contains sixteen
remnants; eight produced by mergers between disk galaxies of equal mass and
eight produced by mergers between disk galaxies with mass ratios of 3:1. The
equal-mass mergers display a wide range of kinematic features, including
counterrotation at large radii, orthogonally rotating cores, and misaligned
rotational axes. Most of the unequal-mass remnants exhibit fairly regular
disk-like kinematics, although two have kinematics more typical of the
equal-mass remnants. Our results may be compared to observations of early type
objects, including ellipticals with misaligned kinematic axes, counterrotating
systems, and S0 galaxies.


title: The MONS Star Trackers

abstract:
  The MONS satellite will have two Star Trackers to sense the spacecraft
attitude, and we plan to use them as scientific instruments to perform
high-precision photometry of thousands of stars. We briefly describe the
current plans for the Star Trackers and their expected capabilities.


title: Prospects for observing pulsating red giants with the MONS Star Trackers

abstract:
  K and M giants show variability on timescales from years down to days and
possibly even hours. I discuss the contribution that can be made with
high-precision photometry that will be obtained by the MONS Star Trackers.
These include observations of flare-like events on Mira variables, and
oscillation spectra for K giants and short-period M giants.


title:
ASCA Observation of the New Transient X-ray Pulsar XTE J0111.2-7317 in
  the Small Magellanic Cloud

abstract:
  The new transient X-ray pulsar XTE J0111.2-7317 was observed with Advanced
Satellite for Cosmology and Astrophysics (ASCA) on 1998 November 18, a few days
after its discovery with the Proportional Counter Array onboard the Rossi X-ray
Timing Explorer. The source was detected at a flux level of 3.6x10^-10 erg
cm^-2 s^-1 in the 0.7--10.0 keV band, which corresponds to the X-ray luminosity
of 1.8x10^38 erg s^-1, if a distance of 65 kpc for this pulsar in the Small
Magellanic Cloud is assumed. Nearly sinusoidal pulsations with a period of
30.9497 +/- 0.0004 s were unambiguously detected during the ASCA observation.
The pulsed fraction is low and slightly energy dependent with average value of
\~27%. The energy spectrum shows a large soft excess below ~2 keV when fitted
to a simple power-law type model. The soft excess is eliminated if the spectrum
is fitted to an ``inversely broken power-law'' model, in which photon indices
below and above a break energy of 1.5 keV are 2.3 and 0.8, respectively. The
soft excess can also be described by a blackbody or a thermal bremsstrahlung
when the spectrum above ~2 keV is modeled by a power-law. In these models,
however, the thermal soft component requires a very large emission zone, and
hence it is difficult to explain the observed pulsations at energies below 2
keV. A bright state of the source enables us to identify a weak iron line
feature at 6.4 keV with an equivalent width of 50 +/- 14 eV. Pulse phase
resolved spectroscopy revealed a slight hardening of the spectrum and marginal
indication of an increase in the iron line strength during the pulse maximum.


title: Atomic Carbon in Galaxies

abstract:
  We present new measurements of the ground state fine-structure line of atomic
carbon at 492 GHz in a variety of nearby external galaxies, ranging from spiral
to irregular, interacting and merging types. In comparison with CO(1-0), the
CI(1-0) intensity stays fairly comparable in the different environments, with
an average value of the ratio of the line integrated areas in Kkm/s of
CI(1-0)/CO(1-0) = 0.2 +/- 0.2. However, some variations can be found within
galaxies, or between galaxies. Relative to CO lines, CI(1-0) is weaker in
galactic nuclei, but stronger in disks, particularly outside star forming
regions. Also, in NGC 891, the CI(1-0) emission follows the dust continuum at
1.3mm extremely well along the full length of the major axis where molecular
gas is more abundant than atomic gas. Atomic carbon therefore appears to be a
good tracer of molecular gas in external galaxies, possibly more reliable than
CO. Atomic carbon can contribute significantly to the thermal budget of
interstellar gas. Cooling due to C and CO amounts typically to 2 x 10^{-5} of
the FIR continuum or 5% of the CII line. However, C and CO cooling reaches 30%
of the gas total, in Ultra Luminous InfraRed Galaxies, where CII is abnormally
faint. Together with CII/FIR, the emissivity ratio CI(1-0)/FIR can be used as a
measure of the non-ionizing UV radiation field in galaxies.


title: A generalized inflation model with cosmic gravitational waves

abstract:
  We propose a $\Lambda$-inflation model which explains a large fraction of the
COBE signal by cosmic gravitational waves. The primordial density perturbations
fulfil both the contraints 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: Sunyaev-Zel'dovich constraints from black hole-seeded proto-galaxies

abstract:
  Recent studies of galactic nuclei suggest that most galaxies are seeded by
super-massive black holes which power the central nucleus. In this picture, the
proto-galactic object is likely to have undergone a very active phase during
which the surrounding medium was shocked and heated up to very high
temperatures. We predict the cosmological effects of this scenario in terms of
the thermal and kinetic Sunyaev-Zel'dovich distortions induced on galactic
scales by a population of proto-galaxies. These predictions are compared to the
observational limit on the mean Compton distortion set by the COBE-FIRAS
instrument. This enables us to derive tight constraints on the fraction of
proto-galaxies seeded by super-massive black holes as well as on the black
hole-to-spheroid mass ratio. Finally, we estimate the contribution of such a
population to the angular power spectrum of the Cosmic Microwave Background
temperature anisotropies on very small angular scales ($l\simeq 10^4-10^5$).


title:
Surface trapping and leakage of low-frequency g-modes in rotating
  early-type stars -- I. Qualitative analysis

abstract:
  A qualitative study of the surface trapping of low-frequency non-radial
g-modes in rotating early-type stars is undertaken within the Cowling,
adiabatic and traditional approximations. It is demonstrated that, at
frequencies below a cut-off, waves cannot be fully trapped within the star, and
will leak through the surface. Expressions for the cut-off frequency are
derived in both the non-rotating and rotating cases; it is found from these
expressions that the cut-off frequency increases with the rotation rate for all
but prograde sectoral modes.
  The results are of possible relevance to the 53 Per and SPB classes of
variable star, which exhibit pulsation frequencies of the same order of
magnitude as the cut-off frequencies found for the stellar model. It is
suggested that observations either of an upper limit on variability periods
(corresponding to the cut-off), or of line-profile variations due to leaking
modes, may permit asteroseismological studies of the outer layers of these
systems.


title: Non-Gaussian signature induced by the SZ effect of galaxy clusters

abstract:
  We apply statistical tests, based on the study of thecoefficients in a
wavelet decomposition, to a cosmological signal: the Cosmic Microwave
Background (CMB) anisotropies. The latter represent the superposition of
primary anisotropy imprints of the initial density perturbations and secondary
anisotropies due to photon interactions after recombination. In an inflationary
scenario with Gaussian distributed fluctuations, we study the statistical
signature of the secondary effects. More specifically, we investigate the
dominant effects arising from the Sunyaev-Zel'dovich effect of galaxy clusters.
Our study predicts the non-Gaussian signature of these secondary anisotropies
and its detectability in the context of the future CMB satellite Planck
Surveyor.


title:
Temporal behaviour of emissions from Gamma-ray bursts and
  optical/near-IR afterglows of GRB 991208 and GRB 991216

abstract:
  The CCD magnitudes in Cousins R and I photometric passbands are determined
for GRB 991216 and GRB 991208 afterglows respectively about 1 and about 3 day
after trigger of the corresponding gamma-ray bursts. Light curves of the
afterglow emissions are obtained by combining the published data with the
present measurements in R and I passbands for GRB 991208 and in R, Gunn I and J
passbands for GRB 991216. They indicate that the flux decay constants of a GRB
are almost the same in each passband with values about 2.2 for GRB 991208 and
about 1.2 for GRB 991216 indicating very fast optical flux decay in the case of
former which may be due to beaming effect. However, cause of steepening by 0.23
+/- 0.06 dex in the R light curve of GRB 991216 afterglow between 2 to 2.5 day
after the burst, is presently not understood. Redshift determinations indicate
that both GRBs are at cosmological distance with a value of 4.2 Gpc for GRB
991208 and 6.2 Gpc for GRB 991216. The observed fluence above 20 keV indicates,
if isotropic, release of energy about 1.3 x 10^{53} erg for GRB 991208 and
about 6.7 x 10^{53} erg for GRB 991216 by these bright gamma-ray flashes. The
enormous amount of released energy will be reduced, if the radiation is beamed
which seems to be case for GRB 991208 afterglow.The quasi-simultaneous
broad-band photometric spectral energy distributions of the afterglows are
determined about 8.5 day and about 35 hour after the bursts of GRB 991208 and
GRB 991216 respectively.The flux decreases exponentially with frequency. The
value of spectral index in the optical-near IR region is -0.75 +/- 0.03 for GRB
991208 and -1.0 +/- 0.12 for GRB 991216.


title: GRB990510: on the possibility of a beamed X-ray afterglow

abstract:
  We discuss the prompt emission of the gamma-ray burst (GRB) 990510 and its
subsequent X-ray afterglow from 8.0 to 44.3 hrs after the prompt emission,
using observations with the Gamma-ray Burst Monitor and Narrow Field
Instruments on BeppoSAX. In the 40-700 keV band, GRB990510 had a fluence of
\~1.9x10^{-5}erg cm^{-2}, whereas it reached a peak flux of ~2.4x10^{-6}erg
cm^{-2} s^{-1}. The X-ray afterglow decay light curve can be satisfactorily
described by a single power law with index of -1.42+/-0.07. Both the X-ray and
optical behaviour of the afterglow can be explained by gamma-ray burst debris
expanding as a jet; we find that the cooling frequency is (fixed) between the
optical and X-ray wavelength bands.


title:
Measuring the galaxy power spectrum and scale-scale correlations with
  multiresolution-decomposed covariance -- I. method

abstract:
  We present a method of measuring galaxy power spectrum based on the
multiresolution analysis of the discrete wavelet transformation (DWT). Since
the DWT representation has strong capability of suppressing the off-diagonal
components of the covariance for selfsimilar clustering, the DWT covariance for
popular models of the cold dark matter cosmogony generally is diagonal, or
$j$(scale)-diagonal in the scale range, in which the second scale-scale
correlations are weak. In this range, the DWT covariance gives a lossless
estimation of the power spectrum, which is equal to the corresponding Fourier
power spectrum banded with a logarithmical scaling. In the scale range, in
which the scale-scale correlation is significant, the accuracy of a power
spectrum detection depends on the scale-scale or band-band correlations. This
is, for a precision measurements of the power spectrum, a measurement of the
scale-scale or band-band correlations is needed. We show that the DWT
covariance can be employed to measuring both the band-power spectrum and second
order scale-scale correlation. We also present the DWT algorithm of the binning
and Poisson sampling with real observational data. We show that the alias
effect appeared in usual binning schemes can exactly be eliminated by the DWT
binning. Since Poisson process possesses diagonal covariance in the DWT
representation, the Poisson sampling and selection effects on the power
spectrum and second order scale-scale correlation detection are suppressed into
minimum. Moreover, the effect of the non-Gaussian features of the Poisson
sampling can be calculated in this frame.


title:
Structure in the local Galactic ISM on scales down to 1 pc, from
  multi-band radio polarization observations

abstract:
  We discuss observations of the linearly polarized component of the diffuse
galactic radio background. These observations, with an angular resolution of
4', were made with the Westerbork Synthesis Radio Telescope (WSRT) in 5
frequency bands in the range 341-375 MHz. The linearly polarized intensity P
(with polarized brightness temperature going up to 10K) shows a `cloudy'
structure, with characteristic scales of 15'-30', which contains relatively
long, but very narrow `canals' (essentially unresolved) in which P is only a
small fraction of that in the neighbouring beams.
  These `canals' are generally seen in more than one frequency band, although
their appearance changes between bands. They are probably due to depolarization
within the synthesized beam, because the change in polarization angle across
the deepest `canals' is in general close to 90 degrees (or 270 etc.). These
very abrupt changes in polarization angle, which are seen only across the
`canals', seem to be accompanied by abrupt changes in the Rotation Measure
(RM), which may have the right magnitude to create the difference of close to
90 degrees in polarization angle, and thereby the `canals'.
  The structure in the polarization maps is most likely due to Faraday rotation
modulation of the probably smooth polarized radiation emitted in the halo of
our Galaxy by the fairly local ISM (up to 500 pc). Therefore, the abrupt
changes of RM across the `canals' provide evidence for very thin (about 1 pc),
and relatively long transition regions in the ISM, across which the RM changes
by as much as 100%. Such drastic RM changes may well be due primarily to abrupt
changes in the magnetic field.


title:
The Predicted Signature of Neutrino Emission in Observations of
  Pulsating Pre-White Dwarf Stars

abstract:
  Pre-white dwarf (PWD) star evolution can be driven by energy losses from
neutrino interactions in the core. Unlike solar neutrinos, these are not the
by-product of nuclear fusion, but instead result from electron scattering
processes in the hot, dense regions of the PWD core. We show that the observed
rate of period change in cool PWD pulsators will constrain neutrino emission in
their cores, and we identify appropriate targets for future observation. Such a
measurement will tell us whether the theories of lepton interactions correctly
describe the production rates and therefore neutrino cooling of PWD evolution.
This would represent the first test of standard lepton theory in dense plasma.


title: A First Look at the Nuclear Region of M31 with Chandra

abstract:
  We report on the first observation of the nuclear region of M31 with the
Chandra X-ray Observatory. The nuclear source seen with the Einstein and ROSAT
HRIs is resolved into five point sources. One of these sources is within 1'' of
the M31 central super-massive black hole. As compared to the other point
sources in M31, this nuclear source has an unusual x-ray spectrum. Based on the
spatial coincidence we identify this source with the central black hole, and
note that the unusual spectrum is a challenge to current theories. A bright
transient is detected ~26'' to the west of the nucleus, which may be associated
with a stellar mass black hole.


title: The European Large Area ISO Survey I: Goals, Definition and Observation

abstract:
  We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest
single Open Time project conducted by ISO, mapping an area of 12 square degrees
at 15mu with ISO-CAM and at 90mu with ISO-PHOT. Secondary surveys in other ISO
bands were undertaken by the ELAIS team within the fields of the primary
survey, with 6 square degrees being covered at 6.7mu and 1 square degree at
175mu. This paper discusses the goals of the project and the techniques
employed in its construction, as well as presenting details of the observations
carried out, the data from which are now in the public domain. We outline the
ELAIS ``Preliminary Analysis'' which led to the detection of over 1000 sources
from the 15 and 90 mu surveys (the majority selected at 15mu with a flux limit
of ~3 mJy), to be fed into a ground-based follow-up campaign, as well as a
programme of photometric observations of detected sources using both ISO-CAM
and ISO-PHOT. We detail how the ELAIS survey complements other ISO surveys in
terms of depth and areal coverage, and show that the extensive multi-wavelength
coverage of the ELAIS fields resulting from our concerted and on-going
follow-up programme has made these regions amongst the best studied areas of
their size in the entire sky, and, therefore, natural targets for future
surveys. This paper accompanies the release of extremely reliable sub-sets of
the ``Preliminary Analysis'' products. Subsequent papers in this series will
give further details of our data reduction techniques, reliability &
completeness estimates and present the 15 and 90 nu number counts from the
``Preliminary Analysis'', while a further series of papers will discuss in
detail the results from the ELAIS ``Final Analysis'', as well as from the
follow-up programme.


title: Steepening of Afterglow Decay for Jets Interacting with Stratified Media

abstract:
  We calculate light-curves for Gamma-Ray Burst afterglows when material
ejected in the explosion is confined to a jet which propagates in a medium with
a power-law density profile. The observed light-curve decay steepens by a
factor of $\Gamma^2$ when an observer sees the edge of the jet. In a uniform
density medium the increase in the power-law index ($\beta$) of the light-curve
as a result of this {\it edge effect} is $\sim0.7$ and is completed over one
decade in observer time. For a pre-ejected stellar wind ($\rho \propto r^{-2}$)
$\beta$ increases by $\sim0.4$ over two decades in time due to the edge effect
and the steepening of the light-curve due to the jet sideways expansion takes
about four decades in time. Therefore, a break in the light-curve for a jet in
a wind model is unlikely to be detected even for very narrow jets of opening
angle of a few degrees or less, in which case the lateral expansion occurs at
early times when the afterglow is bright.
  The light-curve for the afterglow of GRB 990510, for which an increase in
$\beta$ of approximately 1.35 was observed on a time scale of 3 days, cannot be
explained only by the sideways expansion and the edge effects in a jet in a
uniform ISM -- the increase in $\beta$ is too large and too rapid. However, the
passage of the cooling or synchrotron peak frequencies through the observing
band at about 0.1 -- 1 day together with jet edge effect explains the observed
data. The jet opening angle is found to be $\sim 5^o$ and the energy in the
explosion to be less than about $10^{50}$ erg.


title: Gamma-ray Observations of the Galactic Plane at Energies E > 500 GeV

abstract:
  In 1998 and 1999 the Whipple Observatory 10 m telescope was used to search
for diffuse gamma ray emission from the Galactic Plane. No signifiant evidence
of emission was found. Assuming the TeV emission profile matches EGRET
observations above 1 GeV with a differential spectral index of 2.4, we derive
an upper limit of {$\rm {3.0\cdot10^{-8}cm^{-2}s^{-1}sr^{-1}}$} for the average
diffuse emission above {{$\rm500 GeV$}} in the galactic latitude range from
{{$\rm-2^o$ to $\rm +2^o$}} at galactic longitude {{$\rm 40^o$}}. Comparisons
with EGRET observations provide a lower limit of 2.31 for the differential
spectral index of the diffuse emission, assuming there is no break in the
spectrum between 30 GeV and 500 GeV. This constrains models for diffuse
emission with a significant inverse Compton contribution.


title: On Companion-Induced Off-Center Supernova-Like Explosions

abstract:
  We suggest that a neutron star with a strong magnetic field, spiraling into
the envelope of a companion star, can generate a ``companion induced SN-like
off-center explosion". The strongly magnetized neutron star ("magnetar") is
born in a supernova explosion before entering into an expanding envelope of a
supergiant companion. If the neutron star collapses into a black hole via the
hypercritical accretion during the spiral-in phase, a rapidly rotating black
hole with a strong magnetic field at the horizon results. The Blandford-Znajek
power is sufficient to power a supernova-like event with the center of
explosion displaced from the companion core. The companion core, after
explosion, evolves into a C/O-white dwarf or a neutron star with a second
explosion. The detection of highly eccentric black-hole, C/O-white dwarf
binaries or the double explosion structures in the supernova remnants could be
an evidence of the proposed scenario.


title: Supermassive Black Holes in Active Galactic Nuclei

abstract:
  This article gives a brief overview of the direct and indirect evidence in
support of the standard paradigm that active galactic nuclei are powered by
supermassive black holes.


title: Supermassive Black Holes in Inactive Galaxies

abstract:
  This article discusses stellar dynamical evidence for supermassive black
holes in inactive and weakly active galaxies.


title: A Cluster of Black Holes at the Galactic Center

abstract:
  If the stellar population of the bulge contains black holes formed in the
final core collapse of ordinary stars with M \ga 30 M_{\odot}, then about
25,000 stellar mass black holes should have migrated by dynamical friction into
the central parsec of the Milky Way, forming a black hole cluster around the
central supermassive black hole. These black holes can be captured by the
central black hole when they randomly reach a highly eccentric orbit due to
relaxation, either by direct capture (when their Newtonian peribothron is less
than 4 Schwarzschild radii), or after losing orbital energy through
gravitational waves. The overall depletion timescale is ~ 30 Gyr, so most of
the 25,000 black holes remain in the central cluster today. The presence of
this black hole cluster would have several observable consequences. First, the
low-mass, old stellar population should have been expelled from the region
occupied by the black hole cluster due to relaxation, implying a core in the
profile of solar-mass red giants with a radius of ~ 2 pc (i.e., 1'). The
observed central density cusp (which has a core radius of only a few arc
seconds) should be composed primarily of young (\la 1 Gyr) stars. Second,
flares from stars being captured by supermassive black holes in other galaxies
should be rarer than usually expected because the older stars will have been
expelled from the central regions by the black hole clusters of those galaxies.
Third, the young (\la 2 Gyr) stars found at distances ~ 3 - 10 pc from the
Galactic center should be preferentially on highly eccentric orbits. Fourth, if
future high-resolution $K$-band images reveal sources microlensed by the Milky
Way's central black hole, then the cluster black holes could give rise to
secondary (``planet-like'') perturbations on the main event.


title: The origin of cosmic rays: What can GLAST say ?

abstract:
  Gamma rays in the band from 30 MeV to 300 GeV, used in combination with
direct measurements and with data from radio and X-ray bands, provide a
powerful tool for studying the origin of Galactic cosmic rays. Gamma-ray Large
Area Space Telescope (GLAST) with its fine 10-20 arcmin angular resolution will
be able to map the sites of acceleration of cosmic rays and their interactions
with interstellar matter. It will provide information that is necessary to
study the acceleration of energetic particles in supernova shocks, their
transport in the interstellar medium and penetration into molecular clouds.


title: Adenine Abundance in a Collapsing Molecular Cloud

abstract:
  A vital ingredient of DNA molecule named adenine may be produced by
successive addition of HCN during molecular cloud collapse and star formation.
We compute its abundance in a collapsing cloud as a function of the reaction
rate and show that in much of the circumstances the resulting amount may be
sufficient to contaminate planets, comets and meteorites. We introduce a
$f$-parameter which may be used to study the abundance where radiative
association takes place.


title:
Hydrogen-Accreting Carbon-Oxygen White Dwarfs of Low Mass: Thermal and
  Chemical Behavior of Burning Shells

abstract:
  Numerical experiments have been performed to investigate the thermal behavior
of a cooled down white dwarf of initial mass $M_{\rm WD} = 0.516 M_{\sun}$
which accretes hydrogen-rich matter with Z = 0.02 at the rate $\dot{M}=10^{-8}$
\msun \yrm1, typical for a recurrent hydrogen shell flash regime. The evolution
of the main physical quantities of a model during a pulse cycle is examined in
detail. From selected models in the mass range $M_{\rm WD} = 0.52\div 0.68$
\msunend, we derive the borders in the $M_{\rm WD}$ - $\dot{M}$ plane of the
steady state accretion regime when hydrogen is burned at a constant rate as
rapidly as it is accreted. The physical properties during a hydrogen shell
flash in white dwarfs accreting hydrogen-rich matter with metallicities Z =
0.001 and Z = 0.0001 are also studied. For a fixed accretion rate, a decrease
in the metallicity of the accreted matter leads to an increase in the thickness
of the hydrogen-rich layer at outburst and a decrease in the hydrogen-burning
shell efficiency. In the $M_{\rm WD}$-$\dot{M}$ plane, the borders of the
steady state accretion band are critically dependent on the metallicity of the
accreted matter: on decreasing the metallicity, the band is shifted to lower
accretion rates and its width in $\dot{M}$ is reduced.


title:
Spectroscopic identification of ten faint hard X-ray sources discovered
  by Chandra

abstract:
  We report optical spectroscopic identifications of 10 hard (2-10 keV) X-ray
selected sources discovered by Chandra. The X-ray flux of the sources ranges
between 1.5 and 25 x 10-14 cgs, the lower value being 3 times fainter than in
previous BeppoSAX and ASCA surveys. Their R band magnitudes are in the range
12.8-22. Six of the Chandra sources are broad line quasars with redshifts
between 0.42 and 1.19, while the optical identification of the remaining four
is quite varied: two are X-ray obscured, emission line AGN at z=0.272 and
z=0.683, one is a starburst galaxy at z=0.016 and one, most unusually, is an
apparently normal galaxy at z=0.158. These findings confirm and extend down to
fainter X-ray fluxes the BeppoSAX results, in providing samples with a wide
range of X-ray and optical properties. The ratio between the soft X-ray and the
optical luminosity of the z=0.158 galaxy is a factor at least 30 higher than
that of normal galaxies, and similar to those of AGN. The high X-ray luminosity
and the lack of optical emission lines suggest an AGN in which either continuum
beaming dominates, or emission lines are obscured or not efficiently produced.


title: Evidence for topological nonequilibrium in magnetic configurations

abstract:
  We use direct numerical simulations to study the evolution, or relaxation, of
magnetic configurations to an equilibrium state. We use the full single-fluid
equations of motion for a magnetized, non-resistive, but viscous fluid; and a
Lagrangian approach is used to obtain exact solutions for the magnetic field.
As a result, the topology of the magnetic field remains unchanged, which makes
it possible to study the case of topological nonequilibrium. We find two cases
for which such nonequilibrium appears, indicating that these configurations may
develop singular current sheets.


title: Old models for Cygnus X-1 and AGN

abstract:
  Recently, there appeared many papers devoted to the modeling of X-ray
properties of Cygnus X-1 and other black hole accretion disk candidates: e.g.
J.Poutanen, J.Krolik, F.Ryde, MNRAS 292 (1997) L21; E.Agol, J.Krolik, ApJ 507
(1998) 304; A.Beloborodov, in ``High Energy Processes in Accreting Black
Holes'', ASP Conf. Series, 161, (1999), p.295. The goal of this electronic
publication is to draw attention to our old papers where many ideas of recent
discussions were anticipated (hot coronae, Comptonization, photon damping of
waves, particle acceleration and matter ejection from accretion disks with
large scale poloidal magnetic fields, etc.)


title: Recent Progress in Neutron Star Theory

abstract:
  This review contains chapters discussing: Energy density fluctionals of
nuclear matter, Many-body theory of nucleon matter, Hadronic and quark matter,
Mixtures of phases in dense matter, Neutron star observations and predictions.


title:
Intervening O VI Quasar Absorption Systems at Low Redshift: A
  Significant Baryon Reservoir

abstract:
  FUV echelle spectroscopy of the radio-quiet QSO H1821+643 (z = 0.297),
obtained with the Space Telescope Imaging Spectrograph (STIS) at 7 km/s
resolution, reveals 4 definite O VI absorption line systems and one probable O
VI absorber at 0.15 < z(abs) < 0.27. The four definite O VI absorbers are
located near galaxies and are highly displaced from the quasar in redshift;
these are likely intervening systems unrelated to the background QSO. In the
case of the strong O VI system at z(abs) = 0.22497, multiple components are
detected in Si III and O VI as well as H I Lyman series lines, and the
differing component velocity centroids and b-values firmly establish that this
is a multiphase absorption system. A weak O VI absorber is detected at z(abs) =
0.22637, i.e., offset by ~340 km/s from the z(abs) = 0.22497 system. Lya
absorption is detected at z(abs) = 0.22613, but no Lya absorption is
significantly detected at 0.22637. Other weak O VI absorbers at z(abs) =
0.24531 and 0.26659 and the probable O VI system at 0.21326 have widely diverse
O VI/H I column density ratios with N(O VI)/N(H I) ranging from <=0.14+/-0.03
to 5.2+/-1.2. The number density of O VI absorbers with rest equivalent width >
30 mA in the H1821+643 spectrum is remarkably high, dN/dz ~48, with a high
(90%) confidence that it is greater than 17. We conservatively estimate that
the cosmological mass density of the O VI systems Omega_b(O VI) > 0.0008/h_75.
With an assumed metallicity of 1/10 solar and a conservative assumption that
the fraction of oxygen in the O VI ionization stage is 0.2, we obtain Omega_b(O
VI) > 0.004/h_75. This is comparable to the combined cosmological mass density
of stars and cool gas in galaxies and X-ray emitting gas in galaxy clusters at
low redshift.


title:
A new approach to the evolution of cosmological perturbations on large
  scales

abstract:
  We discuss the evolution of linear perturbations about a
Friedmann-Robertson-Walker background metric, using only the local conservation
of energy-momentum. We show that on sufficiently large scales the curvature
perturbation on spatial hypersurfaces of uniform-density is conserved when the
non-adiabatic pressure perturbation is negligible. This is the first time that
this result has been demonstrated independently of the gravitational field
equations. A physical picture of long-wavelength perturbations as being
composed of separate Robertson-Walker universes gives a simple understanding of
the possible evolution of the curvature perturbation, in particular clarifying
the conditions under which super-horizon curvature perturbations may vary.


title:
The Interstellar Medium of Young Stellar Clusters from the Mid-Infrared
  Point of View

abstract:
  Effects of young stellar clusters on their gas and dust environment are
probed using mid-infrared (MIR) wavelengths. The strong MIR [NeIII]/[NeII]
ratios (5 to 10) reveal the presence of current massive stars less than 5 Myr.
Using MIR line ratios along with optical and NIR data from the literature,
composite SEDs are constructed for NGC 1569, NGC 1140 and IIZw40. The stellar
SEDs are then used as input to a dust model to study the impact of the hard,
penetrating radiation field on the dust components, particularly in low
metallicity environments, where the destructive effects of the massive stellar
clusters on the environments occur on global scales. For example, the smallest
dust particles are destroyed over larger regions in the dwarf galaxies than in
normal metallicity starbursts.


title: Dust properties of external galaxies; NGC 891 revisited

abstract:
  We compare 850um SCUBA images of NGC 891 with the corresponding V-band
optical depth predicted from radiation transfer simulations. These two tracers
of dust show a very similar distribution along the minor axis and a reasonable
agreement along the major axis. Assuming that the grains responsible for
optical extinction are also the source of 850um emission we derive a
submillimeter emissivity (emission efficiency) for dust in the NGC 891 disk.
This quantity is found to be a factor of 2-3 higher than the generally-accepted
(but highly uncertain) values adopted for the Milky Way. It should be stated,
however, that if a substantial fraction of dust in NGC 891 is clumped, the
emissivity in the two galaxies may be quite similar. We use our newly-acquired
emissivity to convert our 850um images into detailed maps of dust mass and,
utilizing 21cm and CO-emission data for NGC 891, derive the gas-to-dust ratio
along the disk. We compute an average ratio of 260 -- a value consistent with
the Milky Way and external spirals within the uncertainties in deriving both
the dust mass and the quantity of molecular gas. The bulk of dust in NGC 891
appears to be closely associated with the molecular gas phase although it may
start to follow the distribution of atomic hydrogen at radii >9 kpc (i.e. >0.5
R_25). Using the optical depth of the NGC 891 disk, we quantify how light
emitted at high redshift is attenuated by dust residing in foreground spirals.
For B-band observations of galaxies typically found in the Hubble Deep Field,
the amount of light lost is expected to be small (~ 5%). This value depends
critically on the maximum radial extent of cold dust in spiral disks (which is
poorly known). It may also represent a lower limit if galaxies expel dust over
time into the intergalactic medium.


title: The Kinematics of the Planetary Nebula Population in M94

abstract:
  The planetary nebula populations of relatively nearby galaxies can be easily
observed and provide both a distance estimate and a tool with which dynamical
information can be obtained. Usually the requisite radial velocities are
obtained by multi-object spectroscopy once the planetary nebulae have been
located by direct imaging. Here we report on a technique for measuring
planetary nebula kinematics using the double-beam ISIS spectrograph at the
William Herschel Telescope in a novel slitless mode, which enables the
detection and radial velocity measurements to be combined into a single step.
The results on our first target, the Sab galaxy NGC 4736, allow the velocity
dispersion of the stellar population in a disk galaxy to be traced out to four
scale lengths for the first time and are consistent with a simple isothermal
sheet model.


title: Hadronic blazar models and correlated X-ray/TeV flares

abstract:
  The hypothesis that AGN jets might be the sources of the ultra-high energy
cosmic rays has originally motivated the venture of TeV gamma ray astronomy.
Surprisingly, after the discovery of TeV emission from blazars the attention
has shifted to more traditional explanations which do not involve energetic
hadrons, and there is even common believe that a hadronic interpretation is
disfavored by observations. It is shown here that this is not the case, and
that the currently observed spectra and variability features of blazars can be
perfectly understood within hadronic blazar models. I also discuss how hadronic
models might be observationally distinguished from common leptonic models, and
point out some interesting aspects which could be relevant for the
understanding of the differences between blazar classes.


title: Infrared Classification of Galactic Objects

abstract:
  Unbiased analysis shows that IRAS data reliably differentiate between the
early and late stages of stellar evolution because objects at these stages
clearly segregate in infrared color-color diagrams. Structure in these diagrams
is primarily controlled by the density distribution of circumstellar dust. The
density profile around older objects is the steepest, declining as $r^{-2}$,
while young objects have profiles that vary as $r^{-3/2}$ and flatter. The
different density profiles reflect the different dynamics that govern the
different environments. Our analysis also shows that high mass star formation
is strongly concentrated within \about 5 kpc around the Galactic center, in
support of other studies.


title:
A Remarkable Angular Distribution of the Intermediate Subclass of
  Gamma-Ray Bursts

abstract:
  In the article a test is developed, which allows to test the null-hypothesis
of the intrinsic randomness in the angular distribution of gamma-ray bursts
collected at the Current BATSE Catalog. The method is a modified version of the
well-known counts-in-cells test, and fully eliminates the non-uniform
sky-exposure function of BATSE instrument. Applying this method to the case of
all gamma-ray bursts no intrinsic non-randomness is found. The test also did
not find intrinsic non-randomnesses for the short and long gamma-ray bursts,
respectively. On the other hand, using the method to the new intermediate
subclass of gamma-ray bursts, the null-hypothesis of the intrinsic randomness
for 181 intermediate gamma-ray bursts is rejected on the 96.4% confidence
level. Taking 92 dimmer bursts from this subclass itself, we obtain the
surprising result: This "dim" subclass of the intermediate subclass has an
intrinsic non-randomness on the 99.3% confidence level. On the other hand, the
89 "bright" bursts show no intrinsic non-randomness.


title:
Magellanic-Cloud-Type Interstellar Dust Along Low Density Sightlines in
  the Galaxy

abstract:
  We have studied the UV extinction properties along 30 Galactic sightlines
using data from the International Ultraviolet Explorer (IUE) archive that have
never been previously examined. These distant (d > 1 kpc) sightlines were
selected to investigate the distribution and physical conditions of gas located
in low density regions of the Galactic disk and halo. The average densities
along these sightlines are extremely low. It is likely that they are dominated
by the warm intercloud medium and have little contribution from the cold cloud
medium. We find that a subsample of these sightlines has extinction curves with
weak bumps and very steep far-UV extinction reminiscent of the Magellanic
clouds. These sightlines all lie in the region bounded by 325 < l < 0 and -5 >
b > -11. The gas along these sightlines shows forbidden velocities which may
indicate that the dust has been subject to shocks. This type of low density
sightline may mimic the environments found in the Magellanic Clouds. Large
values of N(Ca II)/N(Na I) indicating low depletion are associated with steep
far-UV extinction. A possible correlation exists between decreasing bump
strength and increasing far-UV steepness for extinction curves in the Galaxy
and the Magellanic Clouds.


title: Convective-Dynamical Instability in Radiation-Supported Accretion Disks

abstract:
  We study radiation-hydrodynamical normal modes of radiation-supported
accretion disks in the WKB limit. It has long been known that in the large
optical depth limit the standard equilibrium is unstable to convection. We
study how the growth rate depends on location within the disk, optical depth,
disk rotation, and the way in which the local dissipation rate depends on
density and pressure. The greatest growth rates are found near the disk
surface. Rotation stabilizes vertical wavevectors, so that growing modes tend
to have nearly-horizontal wavevectors. Over the likely range of optical depths,
the linear growth rate for convective instability has only a weak dependence on
disk opacity. Perturbations to the dissipation have little effect on convective
mode growth rates, but can cause growth of radiation sound waves.


title: The Narrow Line Region of Narrow-Line Seyfert 1 Galaxies

abstract:
  This work studies the optical emission line properties and physical
conditions of the narrow line region (NLR) of seven narrow-line Seyfert 1
galaxies (NLS1). Our results show that the flux carried out by the narrow
component of H-beta is, on average, 50% of the total line flux. As a result,
the [OIII] 5007/H-beta ratio emitted in the NLR varies from 1 to 5, instead of
the universally adopted value of 10. This has strong implications for the
required spectral energy distribution that ionizes the NLR gas. Photoionization
models that consider a NLR composed of a combination of matter-bounded and
ionization-bounded clouds are successful at explaining the low [OIII]
5007/H-beta ratio and the weakness of low-ionization lines of NLS1s. Variation
of the relative proportion of these two type of clouds nicely reproduce the
dispersion of narrow line ratios found among the NLS1 sample. Assuming similar
physical model parameters of both NLS1s and the normal Seyfert 1 galaxy NGC
5548, we show that the observed differences of emission line ratios between
these two groups can be explained in terms of the shape of the input ionizing
continuum. Narrow emission line ratios of NLS1s are better reproduced by a
steep power-law continuum in the EUV -- soft X-ray region, with spectral index
alpha ~ -2. Flatter spectral indices (alpha ~ -1.5) match the observed line
ratios of NGC 5548 but are unable to provide a good match to the NLS1 ratios.
This result is consistent with ROSAT observations of NLS1s, which show that
these objects are characterized by steeper power-law indices than those of Sy1
galaxies with strong broad optical lines.


title: Searching for AGN signatures in Mid-IR Spectra: The case of NGC1068

abstract:
  We present mid-IR observations of the prototypical Seyfert 2 galaxy NGC 1068
obtained with ISOCAM between 5 and 16micron. The proximity of this galaxy
coupled with the spectro-imaging capabilities of the instrument allow us to
separate the mid-IR emission of the active galactic nucleus (AGN) from the
distinctly different emission of the circumnuclear star forming regions. The
Unidentified Infrared Bands (UIBs), which trace the starburst contribution very
well, are not detected in the spectrum of the AGN region where their carriers
could be destroyed. Moreover, the featureless continuum of the AGN exhibits a
strong hot dust component below 10micron not observed in the starburst regions.
Those two distinct mid-IR spectral properties, as well as the presence of high
excitation ionic lines such as [NeVI](7.7micron) and [NeV](14.3micron) in the
AGN spectrum, provide us with very powerful complementary tools to disentangle
AGNs from starbursts. The effects of high extinction on the mid-IR
identification of AGNs are also discussed.


title:
The Evolution of X-ray Clusters and the Entropy of the Intra Cluster
  Medium

abstract:
  The thermodynamics of the diffuse, X-ray emitting gas in clusters of galaxies
is determined by gravitational processes associated with shock heating,
adiabatic compression, and non-gravitational processes such as heating by SNe,
stellar winds, activity in the central galactic nucleus, and radiative cooling.
The effect of gravitational processes on the thermodynamics of the Intra
Cluster Medium (ICM) can be expressed in terms of the ICM entropy S ~
ln(T/\rho^{2/3}). We use a generalized spherical model to compute the X-ray
properties of groups and clusters for a range of initial entropy levels in the
ICM and for a range of mass scales, cosmic epochs and background cosmologies.
We find that the statistical properties of the X-ray clusters strongly depend
on the value of the initial excess entropy. Assuming a constant, uniform value
for the excess entropy, the present-day X-ray data are well fitted for the
following range of values K_* = kT/\mu m_p \rho^{2/3} = (0.4\pm 0.1) \times
10^{34} erg cm^2 g^{-5/3} for clusters with average temperatures kT>2 keV; K_*
= (0.2\pm 0.1) \times 10^{34} erg cm^2 g^{-5/3} for groups and clusters with
average temperatures kT<2 keV. These values correspond to different excess
energy per particle of kT \geq 0.1 (K_*/0.4\times 10^{34}) keV. The dependence
of K_* on the mass scale can be well reproduced by an epoch dependent external
entropy: the relation K_* = 0.8(1+z)^{-1}\times 10^{34} erg cm^2 g^{-5/3} fits
the data over the whole temperature range. Observations of both local and
distant clusters can be used to trace the distribution and the evolution of the
entropy in the cosmic baryons, and ultimately to unveil the typical epoch and
the source of the heating processes.


title: The Evolution of the Stellar Hosts of Radio Galaxies

abstract:
  We present new near-infrared images of z>0.8 radio galaxies from the
flux-limited 7C-III sample of radio sources for which we have recently obtained
almost complete spectroscopic redshifts. The 7C objects have radio luminosities
about 20 times fainter than 3C radio galaxies at a given redshift. The absolute
magnitudes of the underlying host galaxies and their scale sizes are only
weakly dependent on radio luminosity. Radio galaxy hosts at z~2 are
significantly brighter than the hosts of radio-quiet quasars at similar
redshifts and the model AGN hosts of Kauffmann & Haehnelt (2000). There is no
evidence for strong evolution in scale size, which shows a large scatter at all
redshifts. The hosts brighten significantly with redshift, consistent with the
passive evolution of a stellar population that formed at z>~3. This scenario is
consistent with studies of host galaxy morphology and submillimeter continuum
emission, both of which show strong evolution at z>~2.5. The lack of a strong
``redshift cutoff'' in the radio luminosity function to z>4 suggests that the
formation epoch of the radio galaxy host population lasts >~1Gyr from z>~5 to
z~3. We suggest these facts are best explained by models in which the most
massive galaxies and their associated AGN form early due to high baryon
densities in the centres of their dark matter haloes.


title: Detection of H Alpha Emission in a Methane (T-Type) Brown Dwarf

abstract:
  We report the detection of H{$\alpha$} emission in the T dwarf (methane brown
dwarf) 2MASSW J1237392+652615 over three days using the Keck Low Resolution
Imaging Spectrograph. The measured line flux, log(L$_{H{\alpha}}$/L$_{bol}$) =
$-$4.3, is roughly consistent with early M dwarf activity levels and
inconsistent with decreasing activity trends in late M and L dwarfs. Similar
emission is not seen in two other T dwarfs. We speculate on several mechanisms
that may be responsible for emission, including a strong magnetic field,
continuous flaring, acoustic heat generation, and a close ($a$ $\sim$ 4 - 20
R$_{Jup}$) interacting binary, with the cooler component overflowing its Roche
lobe. We suggest that the M9.5Ve PC 0025+0447 could be a warm analogue to 2MASS
J1237+65, and may be powered by the latter mechanism.


title: Timing Noise in SGR 1806-20

abstract:
  We have phase connected a sequence of RXTE PCA observations of SGR 1806-20
covering 178 days. We find a simple secular spin-down model does not adequately
fit the data. The period derivative varies gradually during the observations
between 8.1 and 11.7 * 10^-11 s/s (at its highest, ~40% larger than the long
term trend), while the average burst rate as seen with BATSE drops throughout
the time interval. The phase residuals give no compelling evidence for
periodicity, but more closely resemble timing noise as seen in radio pulsars.
The magnitude of the timing noise, however, is large relative to the noise
level typically found in radio pulsars. Combining these results with the noise
levels measured for some AXPs, we find all magnetar candidates have \Delta_8
values larger than those expected from a simple extrapolation of the
correlation found in radio pulsars. We find that the timing noise in SGR
1806-20 is greater than or equal to the levels found in some accreting systems
(e.g., Vela X-1, 4U 1538-52 and 4U 1626-67), but the spin-down of SGR 1806-20
has thus far maintained coherence over 6 years. Alternatively, an orbital model
with a period P_orb = 733 days provides a statistically acceptable fit to the
data. If the phase residuals are created by Doppler shifts from a
gravitationally bound companion, then the allowed parameter space for the mass
function (small) and orbital separation (large) rule out the possibility of
accretion from the companion sufficient to power the persistent emission from
the SGR.


title:
Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion
  Nebula Cluster

abstract:
  We present the results of a 0.5-0.9" FWHM imaging survey at K (2.2 micron)
and H (1.6 micron) covering 5.1' x 5.1' centered on Theta 1C Ori, the most
massive star in the Orion Nebula Cluster (ONC). At the age and distance of this
cluster, and in the absence of extinction, the hydrogen burning limit (0.08 Mo)
occurs at K~13.5 mag while an object of mass 0.02 Mo has K~16.2 mag. Our
photometry is complete for source detection at the 7 sigma level to K~17.5 mag
and thus is sensitive to objects as low-mass as 0.02 Mo seen through visual
extinction values as high as 10 magnitudes. We use the observed magnitudes,
colors, and star counts to constrain the shape of the inner ONC stellar mass
function across the hydrogen burning limit. After determining the stellar age
and near-infrared excess properties of the optically visible stars in this same
inner ONC region, we present a new technique that incorporates these
distributions when extracting the mass function from the observed density of
stars in the K-(H-K) diagram. We find that our data are inconsistent with a
mass function that rises across the stellar/sub-stellar boundary. Instead, we
find that the most likely form of the inner ONC mass function is one that rises
to a peak around 0.15 Mo, and then declines across the hydrogen-burning limit
with slope N(log M) ~ M^(0.57+/-0.05). We emphasize that our conclusions apply
to the inner 0.71 pc x 0.71 pc of the ONC only; they may not apply to the ONC
as a whole where some evidence for general mass segregation has been found.


title: LINER/H II "Transition" Nuclei and the Nature of NGC 4569

abstract:
  Motivated by the discovery of young, massive stars in the nuclei of some
LINER/H II ``transition'' nuclei such as NGC 4569, we have computed
photoionization models to determine whether some of these objects may be
powered solely by young star clusters rather than by accretion-powered active
nuclei. The models were calculated with the photoionization code CLOUDY, using
evolving starburst continua generated by the the STARBURST99 code of Leitherer
et al. (1999). We find that the models are able to reproduce the emission-line
spectra of transition nuclei, but only for instantaneous bursts of solar or
higher metallicity, and only for ages of ~3-5 Myr, the period when the
extreme-ultraviolet continuum is dominated by emission from Wolf-Rayet stars.
For clusters younger than 3 Myr or older than 6 Myr, and for models with a
constant star-formation rate, the softer ionizing continuum results in an
emission spectrum more typical of H II regions. This model predicts that
Wolf-Rayet emission features should appear in the spectra of transition nuclei.
While such features have not generally been detected to date, they could be
revealed in observations having higher spatial resolution. Demographic
arguments suggest that this starburst model may not apply to the majority of
transition nuclei, particularly those in early-type host galaxies, but it could
account for some members of the transition class in hosts of type Sa and later.
The starburst models during the Wolf-Rayet-dominated phase can also reproduce
the narrow-line spectra of some LINERs, but only under conditions of
above-solar metallicity and only if high-density gas is present (n_e >~ 10^5
cm^{-3}). This scenario could be applicable to some ``Type 2'' LINERs which do
not show any clear signs of nonstellar activity.


title:
Radio continuum emission from the central stars of M20 and the detection
  of a new supernova remnant near M20

abstract:
  The Trifid nebula (M20) is a well-known prominent optical HII region
trisected by obscuring dust lanes. Radio continuum VLA observations of this
Nebula show free-free emission at lambda 3.6 and 6cm from three stellar sources
lying close to the O7V star at the center of the nebula. We argue that neutral
material associated with these stars are photoionized externally by the UV
radiation from the hot central star. We also report the discovery of a
barrel-shaped SNR G7.06--0.12 at the northwest rim of the nebula and two
shell-like features G6.67--0.42 and G6.83--0.21 adjacent to W28 and M20. We
discuss the nature of these features and their possible relationship to the
pulsar PSR 1801-2306 and W28 OH (1720 MHz) masers.


title:
Biases in Expansion Distances of Novae Arising from the Prolate Geometry
  of Nova Shells

abstract:
  (abridged) Expansion distances (or expansion parallaxes) for classical novae
are based on comparing a measurement of the shell expansion velocity,
multiplied by the time since outburst, with some measure of the angular size of
the shell. We review and formalize this method in the case of prolate
spheroidal shells. We present expressions for the maximum line-of-sight
velocity from a complete, expanding shell and for its projected major and minor
axes, in terms of the intrinsic axis ratio and the inclination of the polar
axis to the line of sight. For six distinct definitions of ``angular size'', we
tabulate the error in distance that is introduced under the assumption of
spherical symmetry (i.e., without correcting for inclination and axis ratio).
The errors can be significant and systematic, affecting studies of novae
whether considered individually or statistically. Each of the six estimators
overpredicts the distance when the polar axis is close to the line of sight,
and most underpredict the distance when the polar axis is close to the plane of
the sky. The straight mean of the projected semimajor and semiminor axes gives
the least distance bias for an ensemble of randomly oriented prolate shells.
The best individual expansion distances, however, result from a full
spatio-kinematic modeling of the nova shell. We discuss several practical
complications that affect expansion distance measurements of real nova shells.
Nova shell expansion distances be based on velocity and angular size
measurements made contemporaneously if possible, and the same ions and
transitions should be used for the imaging and velocity measurements. We
emphasize the need for complete and explicit reporting of measurement
procedures and results, regardless of the specific method used.


title:
Smoke Signals From IRC +10216: 1. Milliarcsecond Proper Motions of the
  Dust

abstract:
  The results of a 7-epoch interferometric imaging study, at wavelengths in the
near-infrared K-band, of the carbon star IRC +10216 are presented. The use of
non- and partially-redundant aperture masking techniques on the 10-m Keck-I
telescope has allowed us to produce images of the innermost regions of the
circumstellar dust envelope with unprecedented detail. With roughly twice the
resolving power of previous work, the complex asymmetric structures reported
within the central 0.5 arcsec (20 stellar radii) have been imaged at the size
scale of the stellar disk itself (about 50 mas). A prominent dark lane at a
position angle of approximately 120 deg is suggested to be an optically thick
disk or torus of dust which could help to explain IRC +10216's well-known
bipolarity at a position angle of 20 deg. Observations spanning more than a
pulsational cycle (638 days) have revealed significant temporal evolution of
the nebula, including the outward motion of bright knots and clumps.
Registering these displacements against the compact bright core, which we
tentatively identify as marking the location of the star, has allowed us to
determine the apparent angular velocity at a number of points. The magnitudes
of the proper motions were found to be in agreement with current estimates of
the stellar distance and radial velocity. Higher outflow speeds were found for
features with greater separation from the core. This is consistent with
acceleration taking place over the region sampled by the measurements, however
alternate interpretations are also presented. Although a number of changes of
morphology were found, none were clearly interpreted as the condensation of new
dust over the pulsation cycle.


title:
2.5-11 micron spectroscopy and imaging of AGNs: implication for
  unification schemes

abstract:
  We present 2.5-11 micron spectrophotometric & imaging ISO observations of 28
Sf1, 29 Sf2 & 1 normal galaxy. The Sf1 & Sf2 MIR spectra are statistically
different: Sf1 have a strong power-law continuum of index -0.84+/-0.24 & weak
PAH emission bands. Sf2s have a weak continuum & very strong PAH emission
features with EW (equivalent widths) up to 7.2 micron. On the other hand, the
Sf1 and Sf2 PAH luminosities do not differ statistically and the 7 micron
continuum is ~8 times less luminous in Sf2s than in Sf1s. The PAH emission is
unrelated to the nuclear activity & arises in the bulge ISM. PAH EW are thus a
sensitive nuclear redenning indicator. These results are consistent with
unified schemes & imply that the Sf2 MIR nuclear continuum is, on the average,
extinguished by 92+/-37 visual magnitudes whereas it is directly visible in
Sf1s. The dispersion in Sf2's PAH EW is consistent with the expected spread in
viewing angles. Those Sf2s with PAH EW > 5 micron suffer from > 125 magnitudes
of extinction and are invariably weak X-ray sources. Such Sf2s represent the
highly inclined objects where our line of sight intercepts the full extent of
the torus. About 1/3rd of the Sf2s have PAH EW <= 2 micron, in the range of
Sf1s. Among them, those which have been observed in spectropolarimetry or IR
spectroscopy invariably display "hidden" broad lines. As proposed by Heisler et
al (1997), such Sf2s are most likely seen at grazing incidence such that one
has a direct view of both the "reflecting screen" and the torus inner wall
emitting the MIR continuum. Our observations thus constrain the screen & the
torus inner wall to be spatially co-located. Finally, the 9.7 micron Silicate
feature appears weakly in emission in Sf1s, implying that the torus vertical
thickness cannot significantly exceed E+24 cm-2


title: Nature of the background ultraviolet radiation field

abstract:
  We have tried to determine the flux of the ultraviolet background radiation
field from the column density ratios of various ions in several absorption
systems observed in the spectra of QSOs. We find that in most cases the flux is
considerably higher than what has been estimated to be contributed by the AGNs.
The excess flux could originate locally in hot stars. In a few cases we have
been able to show that such galactic flux can only contribute a part of the
total required flux. The results suggest that the background gets a significant
contribution from an unseen QSO population.


title:
VLBI Astrometry of the Stellar Image of U Herculis, Amplified by the
  1667 OH Maser

abstract:
  The OH 1667 MHz maser in the circumstellar shell around the Mira variable U
Herculis has been observed with the NRAO Very Long Baseline Array (VLBA) at 6
epochs, spread over 4 years. Using phase referencing techniques the position of
the most blue-shifted maser spot was monitored with respect to two
extra-galactic radio sources. The absolute radio positions of the maser can be
compared with the stellar optical position measured by the Hipparcos satellite
to 15 mas accuracy. This confirms the model in which one of the maser spots
corresponds to the stellar continuum, amplified by the maser. The stellar
proper motion and the annual parallax (5.3 +/- 2.1 mas) were measured.


title:
Physical conditions in broad and associated narrow absorption-line
  systems toward APM 08279+5255

abstract:
  Results of a careful analysis of the absorption systems with zabs = zem seen
toward the bright, z_em ~ 3.91, gravitationally lensed quasar APM 08279+5255
are presented. Two of the narrow-line systems, at z_abs = 3.8931 and z_abs =
3.9135, show absorptions from singly ionized species with weak or no NV and O V
absorptions at the same redshift. Absorption due to fine structure transitions
of C II and Si II (excitation energies corresponding to, respectively,
156$\mu$m and 34$\mu$m) are detected at z_abs = 3.8931. Excitation by IR
radiation is favored as the column density ratios are consistent with the shape
of APM 08279+5255 IR spectrum. The low-ionization state of the system favors a
picture where the cloud is closer to the IR source than to the UV source,
supporting the idea that the extension of the IR source is larger than ~ 200
pc. The absence of fine structure lines at z_abs = 3.9135 suggests that the gas
responsible for this system is farther away from the IR source. Abundances are
~ 0.01 and 1$Z_{\odot}$ at z_abs = 3.913 and 3.8931 and aluminum could be
over-abundant with respect to silicon and carbon by at least a factor of two
and five. All this suggests that whereas the \zabs = 3.8931 system is probably
located within 200 pc from the QSO and ejected at a velocity larger than 1000
kms^{-1}, the \zabs = 3.9135 system is farther away and part of the
host-galaxy. (abridged)


title: Semi-Analytic Models for Dark Matter Halos

abstract:
  Various analytic expressions have been proposed for the density profile of
dark matter halos. We consider six of these expressions for which the density
profile has a power-law fall-off rho proportional to r^{-3} at large radii and
a power-law cusp rho proportional to r^{-gamma} (gamma=0, 1/2, 1, 3/2) at small
radii. The phase-space distribution function for these models is calculated
assuming spherical symmetry and either an isotropic velocity dispersion tensor
or an anisotropic dispersion tensor of the type proposed by Osipkov and
Merritt. The differential energy distribution for these models is also derived.
Several applications are discussed including the analysis of dark matter search
experiments and the study of halo formation in a cosmological setting. Analytic
fitting formulae for some of the models are provided.


title: Realizing 3D Spectral Imaging in the Far-Infrared: FIFI LS

abstract:
  We present a progress report on the design and construction of the
Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the SOFIA airborne
observatory. The design of the instrument is driven by the goal of maximizing
observing efficiency, especially for observations of faint, extragalactic
objects. Thus, FIFI LS utilizes an integral field technique that uses slicer
mirrors to optically re-arrange the two-dimensional field into a single slit
for a long slit spectrometer. Effectively, a 5x5 pixel spatial field of view is
imaged to a 25x1 pixel slit and dispersed to a 25x16 pixel, two-dimensional
detector array, providing diffraction-limited spatial and spectral
multiplexing. In this manner, the instrument employs two parallel, medium
resolution (R~2000) grating spectrometers for simultaneous observations in two
bands: a short wavelength band (42 to 110 micron) and a long wavelength band
(110 to 210 micron). Overall, for each of the 25 spatial pixels, the instrument
can cover a velocity range of ~1500 km/s around selected far-infrared lines
with an estimated sensitivity of 2x10^-15 W Hz^1/2 per pixel. This arrangement
provides good spectral coverage with high responsivity.
  ***This paper does not include Figures due to astro-ph size limitations.
Please download entire file at http://fifi-ls.mpe-garching.mpg.de/fifils.ps.gz
****


title:
Significant effects of weak gravitational lensing on determinations of
  the cosmology from Type Ia Supernov\ae

abstract:
  Significant adjustments to the values of the cosmological parameters
estimated from high-redshift Type Ia Supernov\ae data are reported, almost an
order of magnitude greater than previously found. They arise from the effects
of weak gravitational lensing on observations of high-redshift sources. The
lensing statistics used have been obtained from computations of the
three-dimensional shear in a range of cosmological N-body simulations, from
which it is estimated that cosmologies with an underlying deceleration
parameter q_0 = -0.51 +0.03/-0.24 may be interpreted as having q_0 = -0.55
(appropriate to the currently popular cosmology with density parameter
$\Omega_M = 0.3$ and vacuum energy density parameter $\Omega_{\Lambda} = 0.7$).
In addition, the standard deviation expected from weak lensing for the peak
magnitudes of Type Ia Supernov\ae at redshifts of 1 is expected to be
approximately 0.078 magnitudes, and 0.185 magnitudes at redshift 2. This latter
value is greater than the accepted intrinsic dispersion of 0.17 magnitudes.
Consequently, the effects of weak lensing in observations of high-redshift
sources must be taken properly into account.


title: A Numerical Simulation of the Reconnection Layer in 2D Resistive MHD

abstract:
  In this paper we present a two-dimensional, time dependent, numerical
simulation of a reconnection current layer in incompressible resistive
magnetohydrodynamics with uniform resistivity in the limit of very large
Lundquist numbers. We use realistic boundary conditions derived consistently
from the outside magnetic field, and we also take into account the effect of
the back pressure from flow into the the separatrix region. We find that within
a few Alfven times the system evolves from an arbitrary initial state to a
steady state consistent with the Sweet--Parker model, even if the initial state
is Petschek-like.


title: Goodness-of-Fit Analysis of Radial Velocities Surveys

abstract:
  Using eigenmode expansion of the Mark-3 and SFI surveys of cosmological
radial velocities a goodness-of-fit analysis is applied on a mode-by-mode
basis. This differential analysis complements theBayesian maximum likelihood
analysis that finds the most probable model given the data. Analyzing the
surveys with their corresponding most likely models from the CMB-like family of
models, as well as with the currently popular Lambda-CDM model, reveals a
systematic inconsistency of the data with these `best' models. There is a
systematic trend of the cumulative chi^2 to increase with the mode number
(where the modes are sorted by decreasing order of the eigenvalues). This
corresponds to a decrease of the chi^2 with the variance associated with a
mode, and hence with its effective scale. It follows that the differential
analysis finds that on small (large) scales the global analysis of all the
modes `puts' less (more) power than actually required by the data. This
observed trend might indicate one of the followings: a. The theoretical model
(i.e. power spectrum) or the error model (or both) have an excess of power on
large scales; b. Velocity bias; c. The velocity data suffers from still
uncorrected systematic errors.


title:
A Variability Study of Pre-Main Sequence Stars in the Extremely Young
  Cluster IC 348

abstract:
  The extremely young cluster IC 348 has been monitored in the Cousins I band
with a 0.6 m telescope at Wesleyan's Van Vleck Observatory. Photometry of 150
stars was obtained on 76 images taken on 27 separate nights during the period
December, 1998, through March, 1999. As expected, spectral characteristics
largely determine the nature of a star's variability in this cluster. None of
the stars with H-alpha in absorption were found to be variables. On the other
hand, all 16 stars identified as CTTS by their H-alpha emission equivalent
widths and the majority of the 49 WTTS in the part of the cluster we monitored
showed evidence of variability. Nineteen stars were found to be periodic, with
periods ranging from 2.24 to 16.2 days and masses ranging from 0.35 to 1.1
M-sun. Seventeen of these are WTTS and the other 2 are of unknown spectral
class. The period distribution is remarkably similar to what is found in the
Orion Nebula Cluster for stars in the same mass range. Namely, it is bimodal
with peaks at 2-3 days and 7-8 days, although there are not enough periods
known to define these features significantly by the IC 348 data alone. The
three fastest rotators are also the three most massive stars in the periodic
sample.


title:
Fourier power spectra at high frequencies: a way to distinguish a
  neutron star from a black hole

abstract:
  We analyzed the power density spectra of a sample of 9 neutron star and 9
black hole binaries in the low/hard spectral state. In the power density
spectra of accreting neutron stars with a weak magnetic field a significant
power is contained at frequencies close to one kHz. At the same time, most
Galactic accreting black holes demonstrate a strong decline in the power
spectra at the frequencies higher than 10--50 Hz. We propose to use this
empirical fact as a method to distinguish the accreting neutron stars from
black holes in X-ray transients. The X-ray transients that demonstrate
significant noise in their X-ray flux at frequencies above ~500 Hz should be
considered neutron stars. We propose to explain the observed difference as a
result of the existence of a radiation dominated spreading layer on the neutron
star surface (Inogamov & Sunyaev 1999). The possible very high frequency
variabilities of this layer are discussed.


title:
Intrinsic Differences in the Inner Jets of High- and Low-Optically
  Polarized Radio Quasars

abstract:
  A significant fraction of compact radio-loud quasars display most of the
characteristics of relativistically beamed, high-optical polarization blazars,
yet are weakly polarized in the optical regime. We have used the VLBA at 22 and
43 GHz to look for differences in the parsec-scale magnetic field structures of
18 high- and low-optically polarized, compact radio-loud quasars (HPQs and
LPRQs, respectively). We find a strong correlation between the polarization
level of the unresolved parsec-scale radio core at 43 GHz and overall optical
polarization of the source, which suggests a common (possibly co-spatial)
origin for the emission at these two wavelengths. The magnetic fields of the
polarized 43 GHz radio cores are aligned roughly transverse to the jet axis.
Similar orientations are seen in the optical, suggesting that the polarized
flux at both wavelengths is due to one or more strong transverse shocks located
very close to the base of the jet. In LPRQs, these shocks appear to be weak
near the core, and gradually increase in strength down the jet. The LPRQs in
our sample tend to have less luminous radio cores than the HPQs, and jet
components with magnetic fields predominantly parallel to the flow. The
components in HPQ jets, on the other hand, tend to have transverse alignments.
These differences cannot be accounted for by a simple model in which HPQs and
LPRQs are the same type of object, seen at different angles to the line of
sight. A more likely scenario is that LPRQs represent a quiescent phase of
blazar activity, in which the inner jet flow does not undergo strong shocks.


title:
Photometry and Photometric Redshifts of Faint Galaxies in the Hubble
  Deep Field South NICMOS Field

abstract:
  We present a catalog of photometry and photometric redshifts of 335 faint
objects in the HDF-S NICMOS field. The analysis is based on (1) infrared images
obtained with the Hubble Space Telescope (HST) using the Near Infrared Camera
and Multi-Object Spectrograph (NICMOS) with the F110W, F160W, and F222M
filters, (2) an optical image obtained with HST using the Space Telescope
Imaging Spectrograph (STIS) with no filter, and (3) optical images obtained
with the European Southern Observatory (ESO) Very Large Telescope (VLT) with U,
B, V, R, and I filters. The primary utility of the catalog of photometric
redshifts is as a survey of faint galaxies detected in the NICMOS F160W and
F222M images. The sensitivity of the survey varies significantly with position,
reaching a limiting depth of AB(16,000) ~ 28.7 and covering 1.01 arcmin^2 to
AB(16,000) = 27 and 1.05 arcmin^2 to AB(16,000) = 26.5. The catalog of
photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z
> 5, 8 galaxies (or 2% of the total) of redshift z > 10, and 11 galaxies (or 3%
of the total) of best-fit spectral type E/S0, of which 5 galaxies (or 1% of the
total) are of redshift z > 1.


title: Calibration of Nebular Emission-line Diagnostics: II. Abundances

abstract:
  (Abridged) We examine standard methods of measuring nebular chemical
abundances, including estimates based on direct T_e measurements, and also
bright-line diagnostics. We use observations of 4 LMC HII regions whose
ionizing stars have classifications ranging from O7 to WN3. We assume a 2-zone
T_e structure to compute ionic abundances. We compare with photoionization
models tailored to the properties of the individual objects, and emphasize the
importance of correctly relating T_e in the two zones, which can otherwise
cause errors of ~0.2 dex in abundance estimates. There are no spatial
variations to within 0.1 - 0.15 dex in any of the objects, even one hosting 3
WR stars.
  Our data agree with the modeled R23 and S23 diagnostics of O and S. We
present the first theoretical tracks for S23, which are in excellent agreement
with a larger dataset. However, contrary to earlier suggestions, S23 is much
more sensitive to the ionization parameter than is R23, because S23 does not
sample S IV. We therefore introduce S234 = ([SII]+[SIII]+[SIV])/H-beta.
Predicted and observed spatial variations in S234 are dramatically reduced in
contrast to S23. The intensity of [SIV]10.5 microns is easily estimated from a
simple relation between [SIV]/[SIII] and [OIII]/[OII]. This method of
estimating S234 yields excellent agreement with our models, hence we give a
theoretical calibration for S234. The double-valued structure of S23 and S234
remains an important problem as for R23, and presently we consider the S
diagnostics reliable only at Z < 0.5 Z_sol. However, the slightly larger
dynamic range and excellent compatibility with theoretical predictions suggest
the S diagnostics to be more effective abundance indicators than R23.


title: Resonance Paramagnetic Relaxation and Alignment of Small Grains

abstract:
  We show that the energy-level splitting arising from grain rotation ensures
that paramagnetic dissipation acts at its maximum rate, i.e., the conditions
for paramagnetic resonance are automatically fulfilled. We refer to this
process as ``resonance relaxation''. The differences between the predictions of
classical Davis-Greenstein relaxation and resonance relaxation are most
pronounced for grains rotating faster than 1 GHz, i.e., in the domain where
classical paramagnetic relaxation is suppressed. This mechanism can partially
align even very small grains, resulting in linearly polarized microwave
emission which could interfere with efforts to measure the polarization of the
cosmic microwave background.


title: The Balmer Wavelength Range of BP Tauri

abstract:
  We have analyzed all the observations of BP Tauri taken by the International
Ultraviolet Explorer in the low resolution (6 A), long wavelength (from 1850 to
  3350 A) range. This dataset contains 61 spectra. These spectra do not show
any correlation between the continuum flux and the MgII line flux, thus
resolving a standing controversy in the literature concerning the origin of the
MgII line flux. There is no correlation between the color temperature of the UV
continuum and the average value of its flux. Using models of the accretion
process developed by Calvet & Gullbring (1998), we obtain energy fluxes,
accretion spot sizes, and accretion rates from the IUE observations of BP
Tauri. We find average energy fluxes of 5.0 10^11 ergs cm^{-2} s^{-1}, average
spot sizes of 4.4 10^{-3} times the stellar surface, and average accretion
rates of 1.6 10^-8 msun/yr. Our analysis shows that the particle energy flux
and the UV flux in the stellar surface are proportional to each other. Most
strikingly, we observe a correlation between accretion rate and spot size, with
the spot size increasing as the square of the accretion rate. Based on the
results of a simulation, we conclude that geometrical effects are not enough to
account for this effect. Current models of the accretion process fail to
reproduce such an effect, suggesting the need of using more realistic
descriptions of the stellar field when treating magnetospheric accretion. There
may also be an unmodelled efficiency factor that determines how matter is
loaded into the field lines.


title: Physics of Grain Alignment

abstract:
  Aligned grains provide one of the easiest ways to study magnetic fields in
diffuse gas and molecular clouds. How reliable our conclusions about the
inferred magnetic field depends critically on our understanding of the physics
of grain alignment. Although grain alignment is a problem of half a century
standing recent progress achieved in the field makes us believe that we are
approaching the solution of this mystery. I review basic physical processes
involved in grain alignment and show why mechanisms that were favored for
decades do not look so promising right now. I also discuss why the radiative
torque mechanism ignored for more than 20 years looks right now the most
powerful means of grain alignment.


title: Calculation Methods for Radio Pulses from High Energy Showers

abstract:
  We present an approximation for the numerical calculation of Cherenkov radio
pulses in the Fraunhofer limit from very high energy showers in dense media. We
compare it to full Montecarlo simulations in ice studying its range of
applicability and show how it can be extended with a simple algorithm. The
approximation reproduces well the angular distribution of the pulse around the
Cherenkov direction. An improved parameterization for the frequency spectrum in
the Cherenkov direction is given for phenomenolgical applications. We extend
the method to study the pulses produced by showers at distances at which the
Fraunhofer limit does not apply, and give the ranges of distances and
frequencies in which Fraunhofer approximation is good enough for interpreting
future experimental data. Our results are relevant for the detection of very
high energy neutrinos with this technique.


title:
A Survey for Low-mass Stars and Brown Dwarfs in the Upper-Scorpius OB
  Association

abstract:
  The Upper-Scorpius association is the OB association nearest to the Sun (145
pc). Its young age (5 Myr) makes it an ideal place to search for low-mass stars
and brown dwarfs, as these objects should be relatively bright. We have
performed a photometric search for the low-mass members of the association,
using the R, I, and Z filters. The completeness limit is I=18.5 and the
saturation limit is I=13. We obtain 138 candidate members, covering nearly the
entire M spectral type range. We find an excess of brown dwarf candidates over
the number predicted by a Miller-Scalo Initial Mass Function. In addition, we
have performed infrared imaging and low resolution optical spectroscopy of
selected candidates. We find that the infrared observations confirm the
spectral types obtained with the optical photometry. Furthermore, we find
H_alpha in emission in 20 of the 22 objects observed spectroscopically. As
H_alpha is an indicator of youth, we believe that these 20 objects may belong
to the association. One of them, UScoCTIO 128 has a very strong and constant
H_alpha line (equivalent width: -130 A), and its position in the color
magnitude diagram suggests that it is a brown dwarf with mass equal to 0.02
msun. Confirmation of this and the other candidates will have to wait for
higher resolution observations that can reveal spectroscopic mass indicators
like Li I and gravity indicators, such as K I and the subordinate lines of Na
I.


title:
Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky
  Survey (2MASS)

abstract:
  We present JHKs photometry, far red spectra, and spectral classifications for
an additional 67 L dwarfs discovered by the Two Micron All Sky Survey. One of
the goals of this new search was to locate more examples of the latest L
dwarfs. Of the 67 new discoveries, 17 have types of L6 or later. Analysis of
these new discoveries shows that H-alpha emission has yet to be convincingly
detected in any L dwarf later than type L4.5, indicating a decline or absence
of chromospheric activity in the latest L dwarfs. Further analysis shows that
16 (and possibly 4 more) of the new L dwarfs are lithium brown dwarfs and that
the average line strength for those L dwarfs showing lithium increases until
roughly type L6.5 V then declines for later types. This disappearance may be
the first sign of depletion of atomic lithium as it begins to form into
lithium-bearing molecules. Another goal of the search was to locate nearer,
brighter L dwarfs of all subtypes. Using absolute magnitudes for 17 L dwarf
systems with trigonometric parallax measurements, we develop spectrophotometric
relations to estimate distances to the other L dwarfs. Of the 67 new
discoveries, 21 have photometric distances placing them within 25 parsecs of
the Sun. A table of all known L and T dwarfs believed to lie within 25 parsecs
- 53 in total - is also presented. Using the distance measurement of the
coolest L dwarf known, we calculate that the gap in temperature between L8 and
the warmest known T dwarfs is less than 350K and probably much less. If the
transition region between the two classes spans a very small temperature
interval, this would explain why no transition objects have yet been uncovered.
This evidence, combined with model fits to low-resolution spectra of late-M and
early-L dwarfs, indicates that L dwarfs span the range 1300K < Teff < 2000K.


title:
Conversion Law of Infrared Luminosity to Star Formation Rate for
  Galaxies

abstract:
  We construct a new algorithm for estimating the star formation rate (SFR) of
galaxies from their infrared (IR) luminosity by developing the theory of the IR
emission from a dusty H II region.
  The derived formula is ${\rm SFR}/(\MO {\rm yr^{-1}})=\{3.3\times
10^{-10}(1-\eta)/
  (0.4-0.2f+0.6 \epsilon)\}(L{\rm ^{obs}_{IR}}/\LO)$, where $f$ is the fraction
of ionizing photons absorbed by hydrogen,
  $\epsilon$ is the efficiency of dust absorption for nonionizing photons from
OB stars, and $\eta$ is the cirrus fraction of observed IR luminosity.
  The previous conversion formulae of SFR from the IR luminosity is applicable
to only the case where the observed IR luminosity is nearly equal to the
bolometric luminosity (starburst galaxies etc.), except for some empirical
formulae.
  On the other hand, our theoretical SFR is applicable to galaxies even with a
moderate star formation activity.
  That is, our simple and convenient formula is significantly useful for
estimating the SFR of various morphologies and types of galaxies --- from early
elliptical to late spiral and irregular galaxies, or from active starburst to
quiescent galaxies --- as far as they have neither an abnormal dust-to-gas
ratio nor an evident active galactic nucleus.


title:
Problems of the matter increase in our observed expansive and isotropic
  relativistic Universe

abstract:
  The increase in mass of our observed expansive and isotropic relativistic
Universe in the present relativistic cosmology is explained by the extensive
assumption of the matter objects emerging on the horizon (of the most remote
visibility). However, the physical analysis unambiguously shows that this
assumption contradicts the theory of relativity, quantum mechanics, classical
mechanics and observations.


title: HS 0822+3542 - a new nearby extremely metal-poor galaxy

abstract:
  We present the results of spectrophotometry and BVR CCD photometry, as well
as integrated HI radio measurements of a new blue compact galaxy (BCG) HS
0822+3542 with extremely low oxygen abundance: 12+log(O/H) = 7.35, or 1/36 of
solar value. The galaxy is the third most metal-deficient BCG after I Zw 18 and
SBS 0335-052. Its very high mass fraction of gas (~95% of all visible mass) and
blue colours of underlying nebulosity are also similar to those of SBS
0335-052. This suggests that HS 0822+3542 is one of the nearest and dimmest
galaxies experiencing a recently-started first star formation (SF) episode. Its
properties imply that for such galaxies there is a linear scaling of the main
parameters, at least for the baryon mass range (0.3-20)x10^8 M_sun. The total
mass estimate indicates that the galaxy is dynamically dominated by a dark
matter (DM) halo, which itself is one of the least massive for galaxies.


title:
Detectability of Gravitational Radiation from Prompt and Delayed Star
  Collapse to a Black Hole

abstract:
  We consider the emission of gravitational waves in the two proposed models
for the collapse of a massive star to a black hole: the prompt collapse, in
which nearly all the star collapses to a black hole in a dynamical time scale,
and the delayed collapse, in which a light black hole, or a neutron star, which
subsequently accretes matter, forms due to the fall-back achieving, in the
neutron star case, the critical mass for black hole formation. Recent
simulations strongly support this last scenario. We show that, due to the
slowness of fall-back, in the delayed collapse the main burst of gravitational
radiation is emitted depending on the parameters, mass and angular momentum, of
the initial, light, black hole. We estimate, under different assumptions, the
detectability of the emitted gravitational waves showing that such kind of
collapse is not particularly suited for detection by forthcoming
interferometric detectors. Detectors with high sensitivity at frequencies
greater than ~4-5 kHz would be well suited for this kind of sources. We
calculate also the final mass distribution function of single black holes.