title: Effects of Massive Star Formation on the ISM of Dwarf Galaxies

abstract:
  We are studying star formation effects on the properties of the ISM in low
metallicity environments using mid-infrared (MIR) and far-infrared (FIR)
observations of starbursting dwarf galaxies taken with the Infrared Space
Observatory (ISO) and the Kuiper Airborne Observatory (KAO). Effects of the
hard pervasive radiation field on the gas and dust, due to the dust-poor
environments are apparent in both the dust and gas components. From a 158
micron [CII] survey we find enhanced I[CII]/FIR ratios in dwarf galaxies and
I[CII]/I(CO) ratios up to 10 times higher than those for normal metallicity
starburst galaxies. We consider MIR observations in understanding the star
formation properties of dwarf galaxies and constraints on the stellar SED.
Notably, the strong MIR [NeIII]/[NeII] ratios reveal the presence of current
massive stellar populations < 5 My old in NGC1569, NGC1140 and IIZw40. The MIR
unidentified infrared bands (UIBs) are weak, if present at all, as a general
characteristic in low metallicity environments, revealing the destruction of
the smallest carbon particles (e.g. PAHs) over large spatial scales. This is
confirmed with our dust modeling: mass fractions of PAHs are almost negligible
compared to the larger silicate grains emitting in the FIR as well as the small
carbon grains emitting in the MIR, which appear to be the source of the
photoelectric gas heating in these galaxies, in view of the [CII] cooling.


title:
The Primordial Helium Abundance: Towards Understanding and Removing the
  Cosmic Scatter in the dY/dZ Relation

abstract:
  We present results from photoionization models of low-metallicity HII
regions. These nebulae form the basis for measuring the primordial helium
abundance. Our models show that the helium ionization correction factor (ICF)
can be non-negligible for nebulae excited by stars with effective temperatures
larger than 40,000 K. Furthermore, we find that when the effective temperature
rises to above 45,000 K, the ICF can be significantly negative. This result is
independent of the choice of stellar atmosphere. However, if an HII region has
an [O III] 5007/[O I] 6300 ratio greater than 300, then our models show that,
regardless of its metallicity, it will have a negligibly small ICF. A similar,
but metallicity dependent, result was found using the [O III] 5007/H$\beta$
ratio. These two results can be used as selection criteria to remove nebulae
with potentially non-negligible ICFs. Using our metallicity independent
criterion on the data of Izotov & Thuan (1998) results in a 20% reduction of
the rms scatter about the best fit $Y-Z$ line. A fit to the selected data
results in a slight increase of the value of the primordial helium abundance.


title: Gyro-Magnetic Relations and Masses of Stars

abstract:
  The calculations in Thomas-Fermi approximation show that in a gravitational
field each cell of ultra dense matter inside celestial bodies obtains a very
small positive electric charge. A celestial body is electrically neutral as a
whole, because the negative electric charge exists on its surface. On the order
of magnitude the positive volume charge is very small ($10^{-18}e$ only). But
it is sufficient to explain the occurrence of magnetic fields of celestial
bodies and the existence of a discrete spectrum of steady-state values of
masses of stars and pulsars.


title: Compton dragged gamma-ray bursts: the spectrum

abstract:
  We calculate the spectrum resulting from the interaction of a fireball with
ambient soft photons. These photons are assumed to be produced by the walls of
a funnel in a massive star. By parameterizing the radial dependence of the
funnel temperature we calculate the deceleration of the fireball
self-consistently, taking into account the absorption of high energy gamma-rays
due to interaction with the softer ambient photons. The resulting spectrum is
peaked at energies in agreement with observations, has a nu^2 slope in the
X-ray band and a steep power-law high energy tail.


title: A Test of the Collisional Dark Matter Hypothesis from Cluster Lensing

abstract:
  Spergel & Steinhardt proposed the possibility that the dark matter particles
are self-interacting, as a solution to two discrepancies between the
predictions of cold dark matter models and the observations: first, the
observed dark matter distribution in some dwarf galaxies has large,
constant-density cores, as opposed to the predicted central cusps; and second,
small satellites of normal galaxies are much less abundant than predicted. The
dark matter self-interaction would produce isothermal cores in halos, and would
also expel the dark matter particles from dwarfs orbiting within large halos.
However, another inevitable consequence of the model is that halos should
become spherical once most particles have interacted. Here, I rule out this
model by the fact that the innermost regions of dark matter halos in massive
clusters of galaxies are elliptical, as shown by gravitational lensing and
other observations. The absence of collisions in the lensing cores of massive
clusters implies that any dark matter self-interaction is too weak to have
affected the observed density profiles in the dark-matter dominated dwarf
galaxies, or to have eased the destruction of dwarf satellites in galactic
halos. If $s_x$ is the cross section and $m_x$ the mass of the dark matter
particle, then $s_x/m_x < 10^{-25.5} \cm^2/\gev$.


title: The intragroup medium in loose groups of galaxies

abstract:
  We have used the ROSAT PSPC to study the properties of a sample of 24 X-ray
bright galaxy groups, representing the largest sample examined in detail to
date. Hot plasma models are fitted to the spectral data to derive temperatures,
and modified King models are used to characterise the surface brightness
profiles. In agreement with previous work, we find evidence for the presence of
two components in the surface brightness profiles. The extended component is
generally found to be much flatter than that observed in galaxy clusters, and
there is evidence that the profiles follow a trend with system mass. We derive
relationships between X-ray luminosity, temperature and optical velocity
dispersion. The relation between X-ray luminosity and temperature is found to
be L_X \propto T^{4.9}, which is significantly steeper than the same relation
in galaxy clusters. These results are in good agreement with preheating models,
in which galaxy winds raise the internal energy of the gas, inhibiting its
collapse into the shallow potential wells of poor systems.


title:
Relativistic Effects in the Pulse Profile of the 2.5 msec X-Ray Pulsar
  SAX J1808.4-3658

abstract:
  We analyze the properties of the pulsed emission from the accreting
millisecond pulsar SAX J1808.4-3658 in observations of its April 1998 outburst
by the Rossi X-Ray Timing Explorer. Pulse phase spectroscopy shows that the
emission evolves from a hard spectrum (power law with photon index 2.39+-0.06)
to a soft spectrum (index 3.39+-0.24). This softening is also observable as a
phase lag in the fundamental of low-energy photons with respect to high-energy
photons. We show that this lag is roughly constant over ten days of the
outburst. We fit these data with a model where the pulse emission is from a hot
spot on the rotating neutron star and the flux as a function of phase is
calculated including the effects of general relativity. The energy-dependent
lags are very well described by this model. The harder spectra at earlier
phases (as the spot approaches) are the result of larger Doppler boosting
factors which are important for this fast pulsar.


title: Black hole X-ray binaries: A new view on soft-hard spectral transitions

abstract:
  The theory of coronal evaporation predicts the formation of an inner hole in
the cool thin accretion disk for mass accretion rates below a certain value (~
1/50 of the Eddington mass accretion rate) and the sudden disappearance of this
hole when the mass accretion rate rises above that value. The inner edge of the
standard thin disk then suddenly shifts inward from about a few hundred
Schwarzschild radii to the last stable orbit. This appears to quantitatively
account for the observed transitions between hard and soft spectral states at
critical luminosities. Due to the evaporation process the matter accreting in
the geometrically thin disk changes to a hot coronal flow which proceeds
towards the black hole as an advection-dominated accretion flow (ADAF; for a
review see Narayan et al. 1998).


title:
Thomson Thick X-ray Absorption in a Broad Absorption Line Quasar
  PG0946+301

abstract:
  We present a deep ASCA observation of a Broad
  Absorption Line Quasar (BALQSO) PG0946+301. The source was clearly detected
in one of the gas imaging spectrometers, but not in any other detector. If
BALQSOs have intrinsic X-ray spectra similar to normal radio-quiet quasars, our
observations imply that there is Thomson thick X-ray absorption (N_H >~10^{24}
cm^{-2}) toward
  PG0946+301. This is the largest column density estimated so far toward a
BALQSO. The absorber must be at least partially ionized and may be responsible
for attenuation in the optical and UV. If the
  Thomson optical depth toward BALQSOs is close to one, as inferred here, then
spectroscopy in hard X-rays with large telescopes like XMM would be feasible.


title: Gravitational waves from cosmological compact binaries

abstract:
  We consider gravitational waves emitted by various populations of compact
binaries at cosmological distances. We use population synthesis models to
characterize the properties of double neutron stars, double black holes and
double white dwarf binaries as well as white dwarf-neutron star, white
dwarf-black hole and black hole-neutron star systems. We use the
observationally determined cosmic star formation history to reconstruct the
redshift distribution of these sources and their merging rate evolution. The
gravitational signals emitted by each source during its early-inspiral phase
add randomly to produce a stochastic background in the low frequency band with
spectral strain amplitude between 10^{-18} Hz^{-1/2} and
  5 10^{-17} Hz^{-1/2} at frequencies in the interval [5 10^{-6}-5 10^{-5}] Hz.
The overall signal which, at frequencies above 10^{-4}Hz, is largely dominated
by double white dwarf systems, might be detectable with LISA in the frequency
range [1-10] mHz and acts like a confusion limited noise component which might
limit the LISA sensitivity at frequencies above 1 mHz.


title: The Light Elements Be and B as Stellar Chronometers in the Early Galaxy

abstract:
  Recent detailed simulations of Galactic Chemical Evolution have shown that
the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or
absent, correlation with stellar ages in the early Galaxy due to the lack of
efficient mixing of interstellar material enriched by individual Type II
supernovae. A promising alternative "chronometer" of stellar ages is suggested,
based on the expectation that the light elements Be and B are formed primarily
as spallation products of Galactic Cosmic Rays.


title: The Warp of the Galaxy and the Orientation of the LMC Orbit

abstract:
  After studying the orientation of a warp generated by a companion satellite,
we show that the Galactic Warp would be oriented in a different way if the
Magellanic Clouds were its cause. We have treated the problem analytically, and
complemented it with numerical N-Body simulations.


title: Death of Stellar Baryonic Dark Matter

abstract:
  The nature of the dark matter in the haloes of galaxies is one of the
outstanding questions in astrophysics. All stellar candidates, until recently
thought to be likely baryonic contributions to the Halo of our Galaxy, are
shown to be ruled out. Faint stars and brown dwarfs are found to constitute
only a few percent of the mass of the Galaxy. Stellar remnants, including white
dwarfs and neutron stars, are shown to be very constrained as well. High energy
gamma-rays observed in HEGRA data place the strongest constraints, $\Omega_{WD}
< 3 \times 10^{-3} h^{-1}$, where $h$ is the Hubble constant in units of 100 km
s$^{-1}$ Mpc$^{-1}$. Hence one is left with several unanswered questions: 1)
What are MACHOs seen in microlensing surveys? 2) What is the dark matter in our
Galaxy? Indeed a nonbaryonic component in the Halo seems to be required.


title:
Kinematics of Molecular Hydrogen Emission from Planetary and
  Pre-planetary Nebulae

abstract:
  We report results from a program of high-resolution spectral mapping of
rotational H_2 emission from bipolar planetary and pre-planetary nebulae.
Long-slit spectra obtained with the NOAO Phoenix near-infrared spectrometer
allow us to probe the molecular kinematics of these nebulae at moderate spatial
resolution. We find strong evidence of a component of rotation in the
equatorial H_2 emission from the Egg nebula (RAFGL 2688). In this nebula and in
the pre-planetary nebula RAFGL 618, the H_2 kinematics point to the recent
emergence of high-velocity polar flows, which likely mark the fairly sudden
terminations of the red giant phases of their central stars. The classical
bipolar planetary NGC 2346 displays distinct kinematic components, which we
interpret as arising in the morphologically distinct equatorial and polar
regions of the nebula. The H_2 rings observed in the Phoenix position-velocity
maps of this nebula support the hypothesis that ring-like planetaries that
display H_2 emission possess bipolar structure.


title: From Historical Perspectives to Some Modern Possibilities

abstract:
  A historical perspective on the study of asymmetries in planetary nebulae
(PNs) is presented. We also describe our ongoing work in high resolution
spectroscopy of planetaries, and discuss some likely future directions for the
study of asymmetrical PNs.


title: LASCO and EIT Observations of Coronal Mass Ejections

abstract:
  We present a brief overview of LASCO and EIT observations of CMEs. We discuss
CME energetics, the relation of CMEs to streamers and conclude with some
insights into the source regions of CMEs.


title: Stellar Iron Abundances at the Galactic Center

abstract:
  We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 $\pm$ 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 $\pm$ 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.


title:
Structure of the Circumnuclear Region of Seyfert 2 Galaxies Revealed by
  RXTE Hard X-ray Observations of NGC 4945

abstract:
  We report the Rossi X-ray Timing Explorer observations of the heavily
absorbed Seyfert 2 galaxy NGC 4945, which confirm the large column density of
the absorber, corresponding to the optical depth to Thomson scattering of about
2.4. The hard X-ray flux (8-30 keV) measured by us is rapidly variable with a
large amplitude, on time scales of a day or less. This implies that the bulk of
the extreme absorption does not originate in a parsec-size, geometrically thick
molecular torus: limits on the amount of scattered flux require that the
optically thick material on parsec scales must be rather geometrically thin,
subtending a half-angle of less than 10 degrees as seen from the nucleus. This
presents a problem in accounting for the Cosmic X-ray Background primarily with
AGN possessing such geometry.


title: Correlation Statistics of Spectrally-Varying Quantized Noise

abstract:
  I calculate the noise in the measured correlation functions and spectra of
digitized, noiselike signals. In the spectral domain, the signals are drawn
from a Gaussian distribution with variance that depends on frequency. Nearly
all astrophysical signals have noiselike statistics of this type, many with
important spectral variations. The noise is digitized and correlated to form a
measured correlation function, which is then Fourier transformed to produce a
measured spectrum. When averaged over many samples, the elements of the
correlation function and of the spectrum, follow Gaussian distributions. For
each element, the mean of that distribution is the deterministic part of the
measurement. The standard deviation of the Gaussian is the noise. Here I
calculate that noise, as a function of the parameters of digitization. The
noise of the correlation function is related to the underlying spectrum, by
constants that depend on the digitization parameters. Noise affects variances
of elements of the correlation function and covariances between them. In the
spectral domain, noise also produces variances and covariances. I show that
noise is correlated between spectral channels, for digitized spectra, and
calculate the correlation. These statistics of noise are important for
understanding of signals sampled with very high signal-to-noise ratio, or
signals with rapidly-changing levels such as pulsars.


title: An X-ray Flare Detected on the M8 Dwarf VB 10

abstract:
  We have detected an X-ray flare on the very low mass star VB 10 (GL 752 B; M8
V) using the ROSAT High Resolution Imager. VB 10 is the latest type (lowest
mass) main sequence star known to exhibit coronal activity. X-rays were
detected from the star during a single 1.1-ksec segment of an observation which
lasted 22 ksec in total. The energy released by this flare is on the order of
10^27 ergs/sec. This is at least two orders of magnitude greater than the
quiescent X-ray luminosity of VB 10, which has yet to be measured. This X-ray
flare is very similar in nature to the far ultraviolet flare which was observed
by Linsky et al. (1995) using the Goddard High Resolution Spectrograph onboard
Hubble Space Telescope. We discuss reasons for the extreme difference between
the flare and quiescent X-ray luminosities, including the possibility that VB
10 has no quiescent (10^6 K) coronal plasma at all.


title:
HST Images of Stephan's Quintet: Star Cluster Candidates in a Compact
  Group Environment

abstract:
  We present HST WFPC2 images of Stephan's Quintet which encompass three
interacting galaxies and their associated tidal features. These deep,
three-color (B, V, I) images indicate recent, massive stellar system formation
in various regions within the compact group environment. We have identified
star cluster candidates (SCC) both within the interacting galaxies and in the
tidal debris. We compare the SCC colors with stellar population synthesis
models in order to constrain cluster ages, and compare the pattern of formation
of SCC in different regions to the inferred dynamical history of the group.


title: Fast Turbulent Reconnection

abstract:
  Reconnection is the process by which magnetic fields in a conducting fluid
change their topology. This process is essential for understanding a wide
variety of astrophysical processes, including stellar and galactic dynamos and
astrophysical turbulence. To account for solar flares, solar cycles and the
structure of the galactic magnetic field reconnection must be fast, propagating
with a speed close to the Alfven speed. We show that the presence of a random
magnetic field component substantially enhances the reconnection rate and
enables fast reconnection, i.e. reconnection that does not depend on fluid
resistivity. The enhancement of the reconnection rate is achieved via a
combination of two effects. First of all, only small segments of magnetic field
lines are subject to direct Ohmic annihilation. Thus the fraction of magnetic
energy that goes directly into fluid heating goes to zero as fluid resistivity
vanishes. However, the most important enhancement comes from the fact that
unlike the laminar fluid case where reconnection is constrained to proceed line
by line, the presence of turbulence enables many magnetic field lines to enter
the reconnection zone simultaneously. A significant fraction of magnetic energy
goes into MHD turbulence and this enhances reconnection rates through an
increase in the field stochasticity. In this way magnetic reconnection becomes
fast when field stochasticity is accounted for. As a consequence solar and
galactic dynamos are also fast, i.e. do not depend on fluid resistivity.

categories: astro-ph math-ph math.MP physics.flu-dyn physics.geo-ph physics.plasm-ph physics.space-ph


title:
The role of the outer boundary condition in accretion disk models:
  theory and application

abstract:
  The influence of the outer boundary condition (OBC) on the dynamics and
radiation of optically thin accretion flow is investigated. Bremsstrahlung and
synchrotron radiations amplified by Comptonization are taken into account and
two-temperature plasma assumption is adopted. The three OBCs we adopted are the
temperatures of the electrons and ions and the specific angular momentum of the
accretion flow at a certain outer boundary. We find that when the general
parameters such as the mass accretion rate and the viscous parameter are fixed,
the peak flux at various bands such as radio, IR and X-ray, can differ by as
large as several orders of magnitude under different OBCs in our example. Our
results indicate that OBC is both dynamically and radiatively important
therefore should be regarded as a new ``parameter'' in accretion disk models.
We apply the above results to the compact radio source Sgr A* and find that the
discrepancy between the mass accretion rate favored by ADAF models in the
literature and that favored by the three dimensional hydrodynamical simulation
can be naturally resolved by seriously considering the outer boundary condition
of the accretion flow.


title: A New Parameter In Accretion Disk Model

abstract:
  Taking optically thin accretion flows as an example, we investigate the
dynamics and the emergent spectra of accretion flows with different outer
boundary conditions (OBCs) and find that OBC plays an important role in
accretion disk model. This is because the accretion equations describing the
behavior of accretion flows are a set of {\em differential} equations,
therefore, accretion is intrinsically an initial-value problem. We argue that
optically thick accretion flow should also show OBC-dependent behavior. The
result means that we should seriously consider the initial physical state of
the accretion flow such as its angular momentum and its temperature. An
application example to Sgr A$^*$ is presented.


title:
Extragalactic Globular Cluster Systems: A new Perspective on Galaxy
  Formation and Evolution

abstract:
  We present an overview of observational progress in the study of
extragalactic globular cluster systems. Globular clusters turn out to be
excellent tracers not only for the star-formation histories in galaxies, but
also for kinematics at large galactocentric radii. Their properties can be used
to efficiently constrain galaxy formation and evolution. After a brief
introduction of the current methods and futures perspectives, we summarize the
knowledge gained in various areas of galaxy research through the study of
globular clusters. In particular, we address the star-formation histories of
early-type galaxies; globular cluster population in late-type galaxies and
their link to early-type galaxies; star and cluster formation during mergers
and violent interactions; and the kinematics at large radii in early-type
galaxies. The different points are reviewed within the context of galaxy
formation and evolution.
  Finally, we revisit the globular cluster luminosity function as a distance
indicator. Despite its low popularity in the literature, we demonstrate that it
ranks among one of the most precise distance indicators to early-type galaxies,
provided that it is applied properly.


title: Alternative Solutions to Big Bang Nucleosynthesis

abstract:
  Standard big bang nucleosynthesis (SBBN) has been remarkably successful, and
it may well be the correct and sufficient account of what happened. However,
interest in variations from the standard picture come from two sources: First,
big bang nucleosynthesis can be used to constrain physics of the early
universe. Second, there may be some discrepancy between predictions of SBBN and
observations of abundances. Various alternatives to SBBN include inhomogeneous
nucleosynthesis, nucleosynthesis with antimatter, and nonstandard neutrino
physics.


title: VLBI difference astrometry at 43GHz

abstract:
  From 43GHz VLBA observations of the pair of radio sources 1928+738 and
2007+777 we have demonstrated the feasibility of precision phase-delay
differential astrometric techniques at millimeter wavelengths. For a pair of
sources with 5 degrees separation and high antenna elevations, we have shown
that present astrometric models and millimeter arrays are advanced enough to
model the differential phase-delay to within 2 picoseconds, less than one tenth
of a phase-cycle at 43GHz. The root-mean-square of the differential phase-delay
residuals is dominated by the fluctuations of the atmospheric water vapor. We
have determined the relative position of the observed sources with a precision
twofold better than previous determinations at lower frequencies and, more
importantly, largely free from ambiguous definitions of the reference point on
the structure of the radio sources. Our result makes 43GHz VLBI phase-delay
differential astrometry an ideal tool to study the absolute kinematics of the
highly variable structures of regions near the core of extragalactic radio
sources.


title: The Morphological and Structural Classification of Planetary Nebulae

abstract:
  We present a statistical analysis of a complete sample (255) of northern
planetary nebulae (PNe).
  Our analysis is based on morphology as a main parameter.
  The major morphological classes are: round (26 % of the sample), elliptical
(61 %), and bipolar (13 %) PNe.
  About a half of the round and 30 % of the elliptical PNe present multiple
shells.
  Round PNe have higher galactic latitude (| b| = 12) and galactic height
  (<z> = 753 pc), than the elliptical (|b| = 7,<z> = 308 pc) and bipolar (|b| =
3, <z>=179 pc). This possibly implies a different progenitor mass range across
morphology, as a different stellar population would suggest.


title:
Simultaneous Measurements of X-Ray Luminosity and Kilohertz
  Quasi-Periodic Oscillations in Low-Mass X-Ray Binaries

abstract:
  We measure simultaneously the properties of the energy spectra and the
frequencies of the kilohertz quasi-periodic oscillations (QPOs) in fifteen low
mass X-ray binaries covering a wide range of X-ray luminosities. In each source
the QPO frequencies cover the same range of approximately 300 Hz to 1300 Hz,
though the sources differ by two orders of magnitude in their X-ray
luminosities (as measured from the unabsorbed 2-50 keV flux). So the X-ray
luminosity does not uniquely determine the QPO frequency. This is difficult to
understand since the evidence from individual sources indicates that the
frequency and luminosity are very well correlated at least over short
timescales. Perhaps beaming effects or bolometric corrections change the
observed luminosities, or perhaps part of the energy in mass accretion is used
to power outflows reducing the energy emitted in X-rays. It is also possible
that the parameters of a QPO model are tuned in such a way that the same range
of frequencies appears in all sources. Different modes of accretion may be
involved for example (disk and radial) or multiple parameters may conspire to
yield the same frequencies.


title:
On energy spectra of UHE cosmic rays accelerated in supergalactic
  accretion flows

abstract:
  Some ultra-high energy (UHE) cosmic ray (CR) events may be correlated with
the Local Supercluster plane. We consider acceleration of such particles at the
large-scale accretion flows of matter towards such plane and/or accretion flows
onto galaxy clusters. The formed shocks and the general compression flow are
expected to allow for CR diffusive acceleration of UHE particles. For a
simplified flow geometry we consider a stationary acceleration of such CRs and
we discuss influence of model parameters on a particle spectral index. We show
that the general convergent flow pattern leads naturally to very flat proton
spectra with the phase-space spectral indices $\sigma \approx 3.0$, as compared
to the `canonical' shock value of 4.0.


title:
Determination of the EAS Attenuation Length from Data of the ANI
  Experiment

abstract:
  Using the EAS size spectra measured with the MAKET ANI array on Mt. Aragats,
Armenia (3200m a.s.l.) in the range of the shower size 10^5 - 10^7 for
different angles-of-incidence, the EAS attenuation length has been determined
applying different analysis methods. The analysis is based on a data sample of
2.5*10^6 events collected in the period of June, 97 - April, 99. The results
are compared with results deduced from data of the EAS TOP and KASCADE
experiments.


title:
The Dependence of the Age Parameter from EAS Size and Zenith Angle of
  Incidence

abstract:
  The quality of the MAKET-ANI detector installation in view of the uniformity
of the registration efficiency is demonstrated. Based on a data sample
collected by the MAKET-ANI array in the period of June 1997 - March 1999, the
dependencies of the age parameter on the zenith angle and the EAS size
(10^5-10^7) are studied. The variation of the age parameter with the shower
size can be approximately related to the elongation rate.


title: NICMOS Narrow-band Infrared Photometry of TW Hya Association Stars

abstract:
  We have obtained 1.64, 1.90 and 2.15 micron narrow-band images of five T
Tauri stars in the TW Hya Association (TWA) using the Near-Infrared Camera and
Multiobject Spectrometer aboard the Hubble Space Telescope. Most of the T Tauri
stars in our study show evidence of absorption by H2O vapor in their
atmospheres; in addition, the low-mass brown dwarf candidate, TWA 5B, is
brighter at 1.9 microns than predicted by cool star models that include the
effects of H2O vapor but neglect dust. We conclude that the effect of
atmospheric dust on the opacity is important at 1.9 microns for TWA 5B, the
coolest object in our sample. The available evidence suggests that the TWA is
5-15 MY old. Comparison of the colors of TWA 5B with theoretical magnitudes as
a function of age and mass then confirms previous claims that TWA 5B is
substellar with a mass in the range 0.02-0.03 solar masses. The accurate
single-epoch astrometry of the relative positions and separation of TWA 5A and
TWA 5B reported here should permit the direct measurement of the orbital motion
of TWA 5B within only a few years.


title:
Pinpointing the Position of the Post-AGB Star at the Core of RAFGL 2688
  using Polarimetric Imaging with NICMOS

abstract:
  We have used infrared polarimetric imaging with NICMOS to determine precisely
the position of the star that illuminates (and presumably generated) the
bipolar, pre-planetary reflection nebula RAFGL 2688 (the Egg Nebula). The
polarimetric data pinpoint the illuminating star, which is not detected
directly at wavelengths less than or equal to 2 microns, at a position well
within the dark lane that bisects the nebula, 0.55" (about 550 AU) southwest of
the infrared peak which was previously detected at the southern tip of the
northern polar lobe. The inferred position of the central star corresponds to
the geometric center of the tips of the four principle lobes of near-infrared
H2 emission; identifying the central star at this position also reveals the
strong point symmetric structure of the nebula, as seen both in the intensity
and polarization structure of the polar lobes. The polarimetric and imaging
data indicate that the infrared peak directly detected in the NICMOS images is
a self-luminous source and, therefore, is most likely a distant binary
companion to the illuminating star. Although present theory predicts that
bipolar structure in pre-planetary and planetary nebulae is a consequence of
binary star evolution, the separation between the components of the RAFGL 2688
binary system, as deduced from these observations, is much too large for the
presence of the infrared companion to have influenced the structure of the
RAFGL 2688 nebula.


title: Nearby Gas-Rich Low Surface Brightness Galaxies

abstract:
  We examine the Fisher-Tully cz<1000 km/s galaxy sample to determine whether
it is a complete and representative sample of all galaxy types, including low
surface brightness populations, as has been recently claimed. We find that the
sample is progressively more incomplete for galaxies with (1) smaller physical
diameters at a fixed isophote and (2) lower HI masses. This is likely to lead
to a significant undercounting of nearby gas-rich low surface brightness
galaxies. However, through comparisons to other samples we can understand how
the nearby galaxy counts need to be corrected, and we see some indications of
environmental effects that probably result from the local high density of
galaxies.


title:
The Contribution of Faint Blue Galaxies to the Sub-mm Counts and
  Background

abstract:
  Observations in the submillimetre waveband have recently revealed a new
population of luminous, sub-mm sources. These are proposed to lie at high
redshift and to be optically faint due to their high intrinsic dust
obscuration. The presence of dust has been previously invoked in optical galaxy
count models which assume $\tau=9$ Gyr Bruzual & Charlot evolution for spirals
and these fit the count data well from U to K. We now show that by using either
a 1/$\lambda$ or Calzetti absorption law for the dust and re-distributing the
evolved spiral galaxy UV radiation into the far infra-red(FIR), these models
can account for all of the `faint'($\leq1$mJy) $850\mu$m galaxy counts, but
fail to fit 'bright'($\ge2$mJy) sources, indicating that another explanation
for the sub-mm counts may apply at brighter fluxes(e.g. QSOs, ULIRGs). We find
that the main contribution to the faint, sub-mm number counts is in the
redshift range $0.5 < z < 3$, peaking at $z\approx 1.8$. The above model, using
either dust law, can also explain a significant proportion of the
extra-galactic background at $850\mu$m as well as producing a reasonable fit to
the bright $60\mu m$ IRAS counts.


title: The entropy and energy of intergalactic gas in galaxy clusters

abstract:
  Studies of the X-ray surface brightness profiles of clusters, coupled with
theoretical considerations, suggest that the breaking of self-similarity in the
hot gas results from an `entropy floor', established by some heating process,
which affects the structure of the intracluster gas strongly in lower mass
systems. Fitting analytical models for the radial variation in gas density and
temperature to X-ray spectral images from the ROSAT PSPC and ASCA GIS, we
derive gas entropy profiles for 20 galaxy clusters and groups. Scaling these
profiles to coincide in the self-similar case, the lowest mass systems are
found to have higher scaled entropy profiles than more massive systems. This
appears to be due to a baseline entropy of 70-140 h50^-1/3 keV cm^2, depending
on the extent to which shocks have been suppressed in low mass systems. The
extra entropy may be present in all systems, but is detectable only in poor
clusters, compared to the entropy generated by gravitational collapse. This
excess entropy appears to be distributed uniformly with radius outside the
central cooling regions. We determine the energy associated with this entropy
floor, by studying the net reduction in binding energy of the gas in low mass
systems, and find that it corresponds to a preheating temperature of ~0.3 keV.
Since the relationship between entropy and energy injection depends upon gas
density, we can combine the excesses of 70-140 keV cm^2 and 0.3 keV to derive
the typical electron density of the gas into which the energy was injected. The
resulting value of 1-3x10^-4 h50^1/2 cm-3, implies that the heating must have
happened prior to cluster collapse but after a redshift z~7-10. The energy
requirement is well matched to the energy from supernova explosions responsible
for the metals which now pollute the intracluster gas.


title: A submillimetre survey of the star-formation history of radio galaxies

abstract:
  We present the results of the first major systematic submillimetre survey of
radio galaxies spanning the redshift range 1 < z < 5. The primary aim of this
work is to elucidate the star-formation history of this sub-class of elliptical
galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the
JCMT we have obtained 850-micron photometry of 47 radio galaxies to a
consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The
radio galaxy targets have been selected from a series of low-frequency radio
surveys of increasing depth (3CRR, 6CE, etc), in order to allow us to separate
the effects of increasing redshift and increasing radio power on submillimetre
luminosity. Although the dynamic range of our study is inevitably small, we
find clear evidence that the typical submillimetre luminosity (and hence dust
mass) of a powerful radio galaxy is a strongly increasing function of redshift;
the detection rate rises from 15 per cent at z < 2.5 to 75 per cent at z > 2.5,
and the average submillimetre luminosity rises as (1+z)^3 out to z~4. Moreover
our extensive sample allows us to argue that this behaviour is not driven by
underlying correlations with other radio galaxy properties such as radio power,
radio spectral index, or radio source size/age. Although radio selection may
introduce other more subtle biases, the redshift distribution of our detected
objects is in fact consistent with the most recent estimates of the redshift
distribution of comparably bright submillimetre sources discovered in blank
field surveys. The evolution of submillimetre luminosity found here for radio
galaxies may thus be representative of massive ellipticals in general.


title:
X-Ray Spectral and Timing Evolution During the Decay of the 1998
  Outburst from the Recurrent X-Ray Transient 4U 1630-47

abstract:
  We report on the X-ray spectral and timing behavior of the recurrent X-ray
transient 4U 1630-47 for 51 RXTE observations made during the decay of its 1998
outburst. The observations began when the source was still relatively bright,
and, during one of the early observations, a QPO with a non-Lorentzian profile
occurred near 6 Hz. As the source decayed, the X-ray flux dropped exponentially
with an e-folding time of 14.4 d. The exponential decay was interrupted by an
increase in the X-ray flux, and a secondary maximum occurred 89 d after the
onset of the outburst. A transition marked by significant changes in the timing
and spectral properties of the source occurred 104 d after the start of the
outburst. The transition is similar to soft-to-hard state transitions observed
in other black hole candidate X-ray binaries. Most of the changes associated
with the transition occurred in less than 2 d. The timing changes include an
increase in the continuum noise level from less than 4% RMS to greater than 10%
RMS and the appearance of a quasi-periodic oscillation (QPO) at 3.4 Hz with an
RMS amplitude of 7.3% in the 2-21 keV energy band. At the transition, the
energy spectrum also changed with an abrupt drop in the soft component flux in
the RXTE band pass. A change in the power-law photon index from 2.3 to 1.8,
also associated with the transition, occurred over a time period of 8 d. After
the transition, the source flux continued to decrease, and the QPO frequency
decayed gradually from 3.4 Hz to about 0.2 Hz.


title:
Observational Evidence for Massive Black Holes in the Centers of Active
  Galaxies

abstract:
  Naturally occurring water vapor maser emission at 1.35 cm wavelength provides
an accurate probe for the study of accretion disks around highly compact
objects, thought to be black holes, in the centers of active galaxies. Because
of the exceptionally fine angular resolution, 200 microarcseconds, obtainable
with very long baseline interferometry, accompanied by high spectral
resolution, < 0.1 km/s, the dynamics and structures of these disks can be
probed with exceptional clarity. The data on the galaxy NGC4258 are discussed
here in detail. The mass of the black hole binding the accretion disk is 3.9
times 10^7 solar masses. Although the accretion disk has a rotational period of
about 800 years, the physical motions of the masers have been directly measured
with VLBI over a period of a few years. These measurements also allow the
distance from the earth to the black hole to be estimated to an accuracy of 4
percent. The status of the search for other maser/black hole candidates is also
discussed.


title: Binding Energy and the Fundamental Plane of Globular Clusters

abstract:
  A physical description of the fundamental plane of Galactic globular clusters
is developed which explains all empirical trends and correlations in a large
number of cluster observables and provides a small but complete set of truly
independent constraints on theories of cluster formation and evolution in the
Milky Way. Within the theoretical framework of single-mass, isotropic King
models, it is shown that (1) 39 regular (non--core-collapsed) globulars with
measured core velocity dispersions share a common V-band mass-to-light ratio of
1.45 +/- 0.10, and (2) a complete sample of 109 regular globulars reveals a
very strong correlation between cluster binding energy and total luminosity,
regulated by Galactocentric position: E_b \propto (L^{2.05} r_{\rm gc}^{-0.4}).
The observational scatter about either of these two constraints can be
attributed fully to random measurement errors, making them the defining
equations of a fundamental plane for globular clusters. A third, weaker
correlation, between total luminosity and the King-model concentration
parameter, c, is then related to the (non-random) distribution of globulars on
the plane. The equations of the FP are used to derive expressions for any
cluster observable in terms of only L, r_{\rm gc}, and c. Results are obtained
for generic King models and applied specifically to the globular cluster system
of the Milky Way.


title: The Formation History of Globular Clusters

abstract:
  The properties of old globular cluster systems in galaxy halos are used to
infer quantitative constraints on aspects of generic star (cluster) formation.
First, the spatial distribution of globulars in three large galaxies, together
with trends in total cluster population vs. galaxy luminosity for 97 early-type
systems plus the halo of the Milky Way, imply that bound stellar clusters
formed with a universal efficiency throughout early protogalaxies: by mass,
always 0.26% of star-forming gas was converted into globulars rather than halo
field stars. That this fraction is so robust in the face of extreme variations
in local and global galaxy environment suggests that any parcel of gas needs
primarily to exceed a relative density threshold in order to form a bound
cluster of stars. Second, it is shown that a strict, empirical scaling of total
binding energy with luminosity and Galactocentric position is a defining
equation for a fundamental plane of Galactic globular clusters. The
characteristics of this plane, which subsumes all other observable correlations
between the structural parameters of globulars, provide a small but complete
set of facts that must be explained by theories of cluster formation and
evolution in the Milky Way. It is suggested that the E_b(L,r_{\rm gc}) relation
specifically resulted from star formation efficiencies having been
systematically higher inside more massive protoglobular gas clumps.


title: Constraints on Cluster Formation from Old Globular CLuster Systems

abstract:
  The properties of old globular cluster systems (GCSs) in galaxy halos offer
unique insight into the physical processes that conspire to form any generic
star cluster, at any epoch. Presented here is a summary of the information
obtained from (1) the specific frequencies (total populations) and spatial
structures (density vs. galactocentric radius) of GCSs in early-type galaxies,
as they relate to the efficiency (or probability) of bound cluster formation,
and (2) the fundamental role of a scaling between cluster mass and energy among
Galactic globulars in setting their other structural correlations, and the
possible implications for star formation efficiency as a function of mass in
gaseous protoclusters.


title: Relic Neutrinos and Z-Resonance Mechanism for Highest-Energy Cosmic Rays

abstract:
  The origin of the highest-energy cosmic rays remains elusive. The decay of a
superheavy particle (X) into an ultra-energetic neutrino which scatters from a
relic (anti-)neutrino at the Z-resonance has attractive features. Given the
necessary X mass of $10^{14\sim15}$ GeV, the required lifetime, $10^{15\sim16}$
y, renders model-building a serious challenge but three logical possibilities
are considered: (i) X is a Higgs scalar in SU(15) belonging to high-rank
representation, leading to {\it power}-enhanced lifetime; (ii) a global X
quantum number has {\it exponentially}-suppressed symmetry-breaking by
instantons; and (iii) with additional space dimension(s) localisation of X
within the real-world brane leads to {\it gaussian} decay suppression, the most
efficient of the suppression mechanisms considered.


title: Measuring the Size of the Vela Pulsar's Radio Emission Region

abstract:
  We describe measurements of the size of the Vela pulsar via scintillation,
using both fits to the distribution of intensity and measurements of the
modulation index. We briefly discuss systematic effects other than source size
that can affect the distribution, including gain variations, self-noise,
scintillation shot noise, and correlator saturation. Modulation index, a single
number, can be biased by all of these, whereas the distribution of intensity is
affected in different ways by different effects, providing means of
distinguishing among them. Self-noise and gain variations are likely more
important at long observing wavelengths, and correlator saturation and
scintillation shot noise at short wavelengths. We find a size of about 500 km
at decimeter wavelengths. Interestingly, this agrees with measurements of
modulation index by Roberts & Ables at the same wavelength. Their results (and
more recently that reported by Macquart et al.) suggest that size decreases
with increasing wavelength. Although consistent with the observations, this
conclusion is perhaps surprising from the standpoint of the traditional
radius-to-frequency mapping. However, these measurements are of size rather
than height; and of course systematic effects may play a role.


title: Current cosmological constraints from a 10 parameter CMB analysis

abstract:
  We compute the constraints on a ``standard'' 10 parameter cold dark matter
(CDM) model from the most recent CMB and data and other observations, exploring
30 million discrete models and two continuous parameters. Our parameters are
the densities of CDM, baryons, neutrinos, vacuum energy and curvature, the
reionization optical depth, and the normalization and tilt for both scalar and
tensor fluctuations.
  Our strongest constraints are on spatial curvature, -0.24 < Omega_k < 0.38,
and CDM density, h^2 Omega_cdm <0.3, both at 95%. Including SN 1a constraints
gives a positive cosmological constant at high significance.
  We explore the robustness of our results to various assumptions. We find that
three different data subsets give qualitatively consistent constraints. Some of
the technical issues that have the largest impact are the inclusion of
calibration errors, closed models, gravity waves, reionization, nucleosynthesis
constraints and 10-dimensional likelihood interpolation.


title: Fragmentation Instability of Molecular Clouds: Numerical Simulations

abstract:
  We simulate fragmentation and gravitational collapse of cold, magnetized
molecular clouds. We explore the nonlinear development of an instability
mediated by ambipolar diffusion, in which the collapse rate is intermediate to
fast gravitational collapse and slow quasistatic collapse. Initially uniform
stable clouds fragment into elongated clumps with masses largely determined by
the cloud temperature, but substantially larger than the thermal Jeans mass.
The clumps are asymmetric, with significant rotation and vorticity, and lose
magnetic flux as they collapse. The clump shapes, intermediate collapse rates,
and infall profiles may help explain observations not easily fit by
contemporary slow or rapid collapse models.


title:
Numerical simulation of accretion discs in close binary systems and
  discovery of spiral shocks

abstract:
  The history of hydrodynamic numerical simulations for accretion disks in
close binary systems is reviewed, in which emphasis is placed, in particular,
on the facts that spiral shock waves were numerically found in 1986 by
researchers including one of the present authors and that spiral structure was
discovered in IP Pegasi in 1997 by Steeghs et al. The results of our two and
three-dimensional numerical simulations in recent years are then summarized,
with comparison being made with observations.


title:
Water Ice in 2060 Chiron and its Implications for Centaurs and Kuiper
  Belt Objects

abstract:
  We report the detection of water ice in the Centaur 2060 Chiron, based on
near-infrared spectra (1.0 - 2.5 micron) taken with the 3.8-meter United
Kingdom Infrared Telescope (UKIRT) and the 10-meter Keck Telescope. The
appearance of this ice is correlated with the recent decline in Chiron's
cometary activity: the decrease in the coma cross-section allows previously
hidden solid-state surface features to be seen. We predict that water ice is
ubiquitous among Centaurs and Kuiper Belt objects, but its surface coverage
varies from object to object, and thus determines its detectability and the
occurrence of cometary activity.


title: The CDS information hub

abstract:
  The Centre de Donnees astronomiques de Strasbourg (CDS) provides homogeneous
access to heterogeneous information of various origins: information about
astronomical objects in Simbad; catalogs and observation logs in VizieR and in
the catalogue service; reference images and overlays in Aladin; nomenclature in
the Dictionary of Nomenclature; Yellow Page services; the AstroGLU resource
discovery tool; mirror copies of other reference services; and documentation.
With the implementation of links between the CDS services, and with other
on--line reference information, CDS has become a major hub in the rapidly
evolving world of information retrieval in astronomy, developing efficient
tools to help astronomers to navigate in the world-wide `Virtual Observatory'
under construction, from data in the observatory archives to results published
in journals. The WWW interface to the CDS services is available at:
http://cdsweb.u-strasbg.fr/


title: The Broad Line Region in Active Galactic Nuclei

abstract:
  We review constraints on models of the broad line region that are imposed by
observations of the emission lines in Active Galactic Nuclei. Comparison of
high and low ionization lines in sources with FWHM Hbeta < 4000 km/s points
toward low ionization line emission produced in a flattened geometry (the
accretion disk?) with an associated high ionization wind. It remains unclear
whether these results can be extended to all radio quiet AGN and particularly
to radio loud AGN.


title: A phase-reference study of the quasar pair 1038+528A,B

abstract:
  We present results from 3.6 cm observations of the quasar pair 1038+528 A and
B, made in 1995 using the VLBA together with the Effelsberg 100m telescope. We
describe the use of a phase-referencing technique to measure the astrometric
separation between the quasars. We also introduce a new data analysis method
-"hybrid double mapping"- which preserves the relative astrometric information
in a single VLBI hybrid map for close source pairs. We combine our measurements
with those from three previous epochs, the earliest in 1981. Our new
observations confirm the evolution within the structure of quasar B, previously
proposed to explain the measured change in the relative separation of the pair.
Our upper bound for any systematic proper motion between the mass centres of
quasars A and B is 10 micro-arcsec/year. This is set by the limited precision
in defining the reference points in the quasars at different epochs and by
possible instabilities of the source "core" locations. A separate analysis
enables us to put more stringent upper limits to any core motions along the two
source axes.


title: Chemistry in the Envelopes around Massive Young Stars

abstract:
  Recent observational studies of intermediate- and high-mass star-forming
regions at submillimeter and infrared wavelengths are reviewed, and chemical
diagnostics of the different physical components associated with young stellar
objects are summarized. Procedures for determining the temperature, density and
abundance profiles in the envelopes are outlined. A detailed study of a set of
infrared-bright massive young stars reveals systematic increases in the
gas/solid ratios, the abundances of evaporated molecules, and the fraction of
heated ices with increasing temperature. Since these diverse phenomena involve
a range of temperatures from < 100 K to 1000 K, the enhanced temperatures must
be communicated to both the inner and outer parts of the envelopes. This
`global heating' plausibly results from the gradual dispersion of the envelopes
with time. Similarities and differences with low-mass YSOs are discussed. The
availability of accurate physical models will allow chemical models of ice
evaporation followed by `hot core' chemistry to be tested in detail.


title: Geodetic Precession and the Binary Pulsar B1913+16

abstract:
  A change of the component separation in the profiles of the binary pulsar PSR
B1913+16 has been observed for the first time (Kramer 1998) as expected by
geodetic precession. In this work we extend the previous work by accounting for
recent data from the Effelsberg 100-m telescope and Arecibo Observatory and
testing model predictions. We demonstrate how the new information will provide
additional information on the solutions of the system geometry.


title:
Reionization of the Universe and the Photoevaporation of Cosmological
  Minihalos

abstract:
  The first sources of ionizing radiation to condense out of the dark and
neutral IGM sent ionization fronts sweeping outward through their surroundings,
overtaking other condensed objects and photoevaporating them. This feedback
effect of universal reionization on cosmic structure formation is demonstrated
here for the case of a cosmological minihalo of dark matter and baryons exposed
to an external source of ionizing radiation with a quasar-like spectrum, just
after the passage of the global ionization front created by the source. We
model the pre-ionization minihalo as a truncated, nonsingular isothermal sphere
in hydrostatic equilibrium following its collapse out of the expanding
background universe and virialization. Results are presented of the first gas
dynamical simulations of this process, including radiative transfer. A sample
of observational diagnostics is also presented, including the spatially-varying
ionization levels of C, N, and O in the flow if a trace of heavy elements is
present and the integrated column densities of H I, He I and II, and C IV thru
the photoevaporating gas at different velocities which would be measured in
absorption against a background source like that responsible for the
ionization.


title: Red Companions to the z=2.15 Radio Loud Quasar 1550-269

abstract:
  We have conducted observations of the environment around the z=2.15 radio
loud quasar 1550-269 in search of distant galaxies associated either with it or
the z=2.09 CIV absorber along its line of sight. Such objects will be
distinguished by their red colours, R-K > 4.5. We find five such objects in a
1.5 arcmin^2 field around the quasar, with typical K' magnitudes of ~20.4 and
no detected R band emission. We also find a sixth object with K=19.6 +/- 0.3,
and undetected at R, just two arcseconds from the quasar. The nature of all
these objects is currently unclear, and will remain so until we have determined
their redshifts. We suggest that it is likely that they are associated with
either the quasar or the CIV absorber, in which case their properties might be
similar to those of the z=2.38 red Ly-alpha emitting galaxies discovered by
Francis et al. (1997). The small separation between the quasar and the
brightest of our objects suggests that it may be the galaxy responsible for the
CIV metal line absorption system. The closeness to the quasar and the red
colour might have precluded similar objects from being uncovered in previous
searches for emission from CIV and eg. damped absorbers.


title:
The NASA Astrophysics Data System: The Search Engine and its User
  Interface

abstract:
  The ADS Abstract and Article Services provide access to the astronomical
literature through the World Wide Web (WWW). The forms based user interface
provides access to sophisticated searching capabilities that allow our users to
find references in the fields of Astronomy, Physics/Geophysics, and
astronomical Instrumentation and Engineering. The returned information includes
links to other on-line information sources, creating an extensive astronomical
digital library. Other interfaces to the ADS databases provide direct access to
the ADS data to allow developers of other data systems to integrate our data
into their system.
  The search engine is a custom-built software system that is specifically
tailored to search astronomical references. It includes an extensive synonym
list that contains discipline specific knowledge about search term
equivalences.
  Search request logs show the usage pattern of the various search system
capabilities. Access logs show the world-wide distribution of ADS users.
  The ADS can be accessed at http://adswww.harvard.edu


title: The NASA Astrophysics Data System: Data Holdings

abstract:
  Since its inception in 1993, the ADS Abstract Service has become an
indispensable research tool for astronomers and astrophysicists worldwide. In
those seven years, much effort has been directed toward improving both the
quantity and the quality of references in the database. From the original
database of approximately 160,000 astronomy abstracts, our dataset has grown
almost tenfold to approximately 1.5 million references covering astronomy,
astrophysics, planetary sciences, physics, optics, and engineering. We collect
and standardize data from approximately 200 journals and present the resulting
information in a uniform, coherent manner. With the cooperation of journal
publishers worldwide, we have been able to place scans of full journal articles
on-line back to the first volumes of many astronomical journals, and we are
able to link to current version of articles, abstracts, and datasets for
essentially all of the current astronomy literature. The trend toward
electronic publishing in the field, the use of electronic submission of
abstracts for journal articles and conference proceedings, and the increasingly
prominent use of the World Wide Web to disseminate information have enabled the
ADS to build a database unparalleled in other disciplines.
  The ADS can be accessed at http://adswww.harvard.edu


title: The NASA Astrophysics Data System: Overview

abstract:
  The NASA Astrophysics Data System Abstract Service has become a key component
of astronomical research. It provides bibliographic information daily, or near
daily, to a majority of astronomical researchers worldwide.
  We describe the history of the development of the system and its current
status.
  We show several examples of how to use the ADS, and we show how ADS use has
increased as a function of time. Currently it is still increasing
exponentially, with a doubling time for number of queries of 17 months.
  Using the ADS logs we make the first detailed model of how scientific
journals are read as a function of time since publication.
  The impact of the ADS on astronomy can be calculated after making some simple
assumptions. We find that the ADS increases the efficiency of astronomical
research by 333 Full Time Equivalent (2000 hour) research years per year, and
that the value of the early development of the ADS for astronomy, compared with
waiting for mature technologies to be adopted, is 2332 FTE research years.
  The ADS is available at http://adswww.harvard.edu/.


title: The NASA Astrophysics Data System: Architecture

abstract:
  The powerful discovery capabilities available in the ADS bibliographic
services are possible thanks to the design of a flexible search and retrieval
system based on a relational database model. Bibliographic records are stored
as a corpus of structured documents containing fielded data and metadata, while
discipline-specific knowledge is segregated in a set of files independent of
the bibliographic data itself.
  The creation and management of links to both internal and external resources
associated with each bibliography in the database is made possible by
representing them as a set of document properties and their attributes.
  To improve global access to the ADS data holdings, a number of mirror sites
have been created by cloning the database contents and software on a variety of
hardware and software platforms.
  The procedures used to create and manage the database and its mirrors have
been written as a set of scripts that can be run in either an interactive or
unsupervised fashion.
  The ADS can be accessed at http://adswww.harvard.edu


title: Thermal Instability and the Formation of Clumpy Gas Clouds

abstract:
  The radiative cooling of optically thin gaseous regions and the formation of
a two-phase medium and of cold gas clouds with a clumpy substructure is
investigated. In optically thin clouds, the growth rate of small isobaric
density perturbations is independent of their length scale. However, the growth
of a perturbation is limited by its transition from isobaric to isochoric
cooling. The temperature at which this transition occurs decreases with the
length scale of the perturbation. Consequently small scale perturbations have
the potential to reach higher amplitudes than large scale perturbations. When
the amplitude becomes nonlinear, advection overtakes the pressure gradient in
promoting the compression resulting in an accelerated growth of the
disturbance. The critical temperature for transition depends on the initial
amplitude. The fluctuations which can first reach nonlinearity before their
isobaric to isochoric transition will determine the characteristic size and
mass of the cold dense clumps which would emerge from the cooling of an
initially nearly homogeneous region of gas. Thermal conduction is in general
very efficient in erasing isobaric, small-scale fluctuations, suppressing a
cooling instability. A weak, tangled magnetic field can however reduce the
conductive heat flux enough for low-amplitude fluctuations to grow isobarically
and become non-linear if their length scales are of order 0.01 pc. Finally, we
demonstrate how a 2-phase medium, with cold clumps being pressure confined in a
diffuse hot residual background component, would be sustained if there is
adequate heating to compensate the energy loss.


title:
Infrared spectroscopy of NGC 1068: Probing the obscured ionizing AGN
  continuum

abstract:
  The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of
the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a
compilation of UV to IR narrow emission line data to determine the spectral
energy distribution (SED) of the obscured extreme-UV continuum that
photoionizes the narrow line emitting gas in the active galactic nucleus. We
search a large grid of gas cloud models and SEDs for the combination that best
reproduces the observed line fluxes and NLR geometry. Our best fit model
reproduces the observed line fluxes to better than a factor of 2 on average and
is in general agreement with the observed NLR geometry. It has two gas
components that are consistent with a clumpy distribution of dense outflowing
gas in the center and a more extended distribution of less dense and more
clumpy gas farther out that has no net outflow. The best fit SED has a deep
trough at ~4 Ryd, which is consistent with an intrinsic Big Blue Bump that is
partially absorbed by ~6x10^19 cm^-2 of neutral hydrogen interior to the NLR.


title:
The Nature of Associated Absorption and the UV-X-ray Connection in 3C
  288.1

abstract:
  We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar,
3C 288.1. The data cover ~590 A to ~1610 A in the quasar rest frame. They
reveal a wealth of associated absorption lines (AALs) with no accompanying
Lyman-limit absorption. The metallic AALs range in ionization from C III and N
III to Ne VIII and Mg X. We use these data and photoionization models to derive
the following properties of the AAL gas: 1) There are multiple ionization zones
within the AAL region, spanning a factor of at least ~50 in ionization
parameter. 2) The overall ionization is consistent with the ``warm'' X-ray
continuum absorbers measured in Seyfert 1 nuclei and other QSOs. However, 3)
the column densities implied by the AALs in 3C 288.1 are too low to produce
significant bound-free absorption at any UV-X-ray wavelengths. Substantial
X-ray absorption would require yet another zone, having a much higher
ionization or a much lower velocity dispersion than the main AAL region. 4) The
total hydrogen column density in the AAL gas is log N_H (cm-2)= 20.2. 5) The
metallicity is roughly half solar. 6) The AALs have deconvolved widths of ~900
km/s and their centroids are consistent with no shift from the quasar systemic
velocity (conservatively within +/-1000 km/s). 7) There are no direct
indicators of the absorber's location in our data, but the high ionization and
high metallicity both suggest a close physical relationship to the quasar/host
galaxy environment. Finally, the UV continuum shape gives no indication of a
``blue bump'' at higher energies. There is a distinct break of unknown origin
at ~1030 A, and the decline toward higher energies (with spectral index alpha =
-1.73, for f_nu ~ nu^alpha) is even steeper than a single power-law
interpolation from 1030 A to soft X-rays.


title: The ALADIN Interactive Sky Atlas

abstract:
  The Aladin interactive sky atlas, developed at CDS, is a service providing
simultaneous access to digitized images of the sky, astronomical catalogues,
and databases.
  The driving motivation is to facilitate direct, visual comparison of
observational data at any wavelength with images of the optical sky, and with
reference catalogues.
  The set of available sky images consists of the STScI Digitized Sky Surveys,
completed with high resolution images of crowded regions scanned at the MAMA
facility in Paris.
  A Java WWW interface to the system is available at:
http://aladin.u-strasbg.fr/


title: The SIMBAD astronomical database

abstract:
  Simbad is the reference database for identification and bibliography of
astronomical objects. It contains identifications, `basic data', bibliography,
and selected observational measurements for several million astronomical
objects. Simbad is developed and maintained by CDS, Strasbourg. Building the
database contents is achieved with the help of several contributing institutes.
Scanning the bibliography is the result of the collaboration of CDS with
bibliographers in Observatoire de Paris (DASGAL), Institut d'Astrophysique de
Paris, and Observatoire de Bordeaux. When selecting catalogues and tables for
inclusion, priority is given to optimal multi-wavelength coverage of the
database, and to support of research developments linked to large projects. In
parallel, the systematic scanning of the bibliography reflects the diversity
and general trends of astronomical research.
  A WWW interface to Simbad is available at: http://simbad.u-strasbg.fr/Simbad


title: Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths

abstract:
  We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet
(FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology
as a function of wavelength. This sample, which includes a range of classical
Hubble types from elliptical to irregular with emphasis on spirals at low
inclination angle, provides a valuable database for comparison with images of
high-z galaxies whose FUV light is redshifted into the optical and near-
infrared bands. Ultraviolet data are from the UIT Astro-2 mission. We present
images and surface brightness profiles for each galaxy, and we discuss the
wavelength-dependence of morphology for different Hubble types in the context
of understanding high-z objects. In general, the dominance of young stars in
the FUV produces the patchy appearance of a morphological type later than that
inferred from optical images. Prominent rings and circumnuclear star formation
regions are clearly evident in FUV images of spirals, while bulges, bars, and
old, red stellar disks are faint to invisible at these short wavelengths.
However, the magnitude of the change in apparent morphology ranges from
dramatic in early--type spirals with prominent optical bulges to slight in
late-type spirals and irregulars, in which young stars dominate both the UV and
optical emission. Starburst galaxies with centrally concentrated, symmetric
bursts display an apparent ``E/S0'' structure in the FUV, while starbursts
associated with rings or mergers produce a peculiar morphology. We briefly
discuss the inadequacy of the optically-defined Hubble sequence to describe FUV
galaxy images and estimate morphological k-corrections, and we suggest some
directions for future research with this dataset.


title:
Approximations of the self-similar solution for blastwave in a medium
  with power-law density variation

abstract:
  Approximations of the Sedov self-similar solution for a strong point
explosion in a medium with the power-law density distribution \rho^o\propto
r^{-m} are reviewed and their accuracy are analyzed. Taylor approximation is
extended to cases m\neq 0. Two approximations of the solution are presented in
the Lagrangian coordinates for spherical, cylindrical and plane geometry. These
approximations may be used for the investigation of the ionization structure of
the adiabatic flow, i.e., inside adiabatic supernova remnants.


title:
Search and Discovery Tools for Astronomical On-line Resources and
  Services

abstract:
  A growing number of astronomical resources and data or information services
are made available through the Internet. However valuable information is
frequently hidden in a deluge of non-pertinent or non up-to-date documents. At
a first level, compilations of astronomical resources provide help for
selecting relevant sites. Combining yellow-page services and meta-databases of
active pointers may be an efficient solution to the data retrieval problem.
Responses generated by submission of queries to a set of heterogeneous
resources are difficult to merge or cross-match, because different data
providers generally use different data formats: new endeavors are under way to
tackle this problem. We review the technical challenges involved in trying to
provide general search and discovery tools, and to integrate them through upper
level interfaces.


title: R-mode runaway and rapidly rotating neutron stars

abstract:
  We present a simple spin evolution model that predicts that rapidly rotating
accreting neutron stars will mainly be confined to a narrow range of
spin-frequencies; P= 1.5-5 ms. This is in agreement with current observations
of both neutron stars in the Low-Mass X-ray Binaries and millisecond
radiopulsars. The main ingredients in the model are; i) the instability of
r-modes above a critical spin rate, ii) thermal runaway due to heat released as
viscous damping mechanisms counteract the r-mode growth, and iii) a revised
estimate of the strength of dissipation due to the presence of a viscous
boundary layer at the base of the crust in an old and relatively cold neutron
star. We discuss the gravitational waves that are radiated during the brief
r-mode driven spin-down phase. We also briefly touch on how the new estimates
affects the predicted initial spin periods of hot young neutron stars.


title: Radio Emission Properties of Millisecond Pulsars

abstract:
  We report the most recent progress in understanding the emission properties
of millisecond pulsars.


title:
Interplanetary Network Localization of GRB991208 and the Discovery of
  its Afterglow

abstract:
  The extremely energetic (~10^-4 erg/cm^2) gamma-ray burst (GRB) of 1999
December 8 was triangulated to a ~14 sq. arcmin. error box ~1.8 d after its
arrival at Earth with the 3rd interplanetary network (IPN), consisting of the
Ulysses, Near Earth Asteroid Rendezvous (NEAR), and WIND spacecraft. Radio
observations with the Very Large Array ~2.7 d after the burst revealed a bright
fading counterpart whose position is consistent with that of an optical
transient source whose redshift is z=0.707. We present the time history, peak
flux, fluence, and refined 1.3 sq. arcmin. error box of this event, and discuss
its energetics. This is the first time that a counterpart has been found for a
GRB localized only by the IPN.


title: The Effelsberg Search for Pulsars in the Galactic Centre

abstract:
  We report the status of a search for pulsars in the Galactic Centre, using a
completely revised and improved high-sensitivity double-horn system at
4.85-GHz. We also present calculations about the success rate of periodicity
searches for such a survey, showing that in contrast to conclusions in recent
literature pulsars can be indeed detected at the chosen search frequency.


title:
Near Infrared Photometry of Galactic Globular Clusters M56 and M15.
  Extending the Red Giant Branch vs. Metallicity Calibration Towards Metal Poor
  Systems

abstract:
  Infrared JKs-band photometry of the Galactic globular clusters M15 and, for
the first time, M56 is presented. We estimated the reddening
(E(B-V)=0.18+/-0.08 mag) and distance modulus ((m-M)_V=15.43+/-0.30 mag)
towards the poorly studied globular cluster M56. We combined our data with
observations of other clusters from the literature (12 in total) to extend the
[Fe/H] vs. Red Giant Branch (RGB) slope relation towards metal-poor clusters.
Our best fit yields to [Fe/H]=-3.40(+/-0.22)-27.74(+/-2.35)x(RGB Slope), with
an r.m.s.=0.20. The broader metallicity baseline greatly reduced the
uncertainties compared to other existing calibrations. We confirmed a
previously obtained calibration of the relation between the RGB color
(J-Ks)_0(RGB) at M_Ks=-5.5 vs. [Fe/H]:
[Fe/H]=-6.90(+/-0.99)+6.63(+/-1.05)x(J-Ks)_0(RGB) with an r.m.s.=0.33. Finally,
using the new RGB slope calibration we estimated the abundance of the super
metal-rich cluster Liller 1 [Fe/H]=+0.34+/-0.22.


title:
Rotations and Abundances of Blue Horizontal-Branch Stars in Globular
  Cluster M15

abstract:
  High-resolution optical spectra of eighteen blue horizontal-branch (BHB)
stars in the globular cluster M15 indicate that their stellar rotation rates
and photospheric compositions vary strongly as a function of effective
temperature. Among the cooler stars in the sample, at Teff ~ 8500 K, metal
abundances are in rough agreement with the canonical cluster metallicity, and
the v sin i rotations appear to have a bimodal distribution, with eight stars
at v sin i < 15 km/s and two stars at v sin i ~ 35 km/s. Most of the stars at
Teff > 10000 K, however, are slowly rotating, v sin i < 7 km/s, and their iron
and titanium are enhanced by a factor of 300 to solar abundance levels.
Magnesium maintains a nearly constant abundance over the entire range of Teff,
and helium is depleted by factors of 10 to 30 in three of the hotter stars.
Diffusion effects in the stellar atmospheres are the most likely explanation
for these large differences in composition. Our results are qualitatively very
similar to those previously reported for M13 and NGC 6752, but with even larger
enhancement amplitudes, presumably due to the increased efficiency of radiative
levitation at lower intrinsic [Fe/H]. We also see evidence for faster stellar
rotation explicitly preventing the onset of the diffusion mechanisms among a
subset of the hotter stars.


title: The Magellanic Clouds and the Primordial Helium Abundance

abstract:
  A new determination of the pregalactic helium abundance based on the
Magellanic Clouds H II regions is discussed. This determination amounts to Yp =
0.2345 +- 0.0030 and is compared with those derived from giant extragalactic H
II regions in systems with extremely low heavy elements content. It is
suggested that the higher primordial value derived by other authors from giant
H II region complexes could be due to two systematic effects: the presence of
neutral hydrogen inside the helium Stromgren sphere and the presence of
temperature variations inside the observed volume.


title:
Observations of Faint, Hard-Band X-ray Sources in the Field of CRSS
  J0030.5+2618 with the Chandra X-ray Observatory and the Hobby-Eberly
  Telescope

abstract:
  We present results from a study of 2-8 keV X-ray sources detected by the
Advanced CCD Imaging Spectrometer (ACIS) instrument on the Chandra X-ray
Observatory in the field of the z=0.516 cluster CRSS J0030.5+2618. In our 63.5
arcmin^2 search area, we detect 10 sources with 2-8 keV fluxes down to
approximately 4x10^{-15} erg cm^{-2} s$^{-1}; our lowest flux sources are
approximately 10 times fainter than those previously available for study in
this band. Our derived source density is about an order of magnitude larger
than previous source counts above 2 keV, although this density may be enhanced
somewhat due to the presence of the cluster. We detail our methods for source
detection and characterization, and we show that the resulting source list and
parameters are robust. We have used the Marcario Low Resolution Spectrograph on
the Hobby-Eberly Telescope to obtain optical spectra for several of our
sources; combining these spectra with archival data we find that the sources
appear to be active galaxies, often with narrow permitted lines, red optical
continua or hard X-ray spectra. Four of the X-ray sources are undetected to
R=21.7; if they reside in L* galaxies they must have z > 0.55-0.75 and hard
X-ray luminosities of L_{2-8} > 4x10^{42} erg s^{-1}. We detect all but one of
our 2-8 keV sources in the 0.2-2 keV band as well. This result extends to
significantly lower fluxes the constraints on any large, completely new
population of X-ray sources that appears above 2-3 keV.


title: The VizieR database of Astronomical Catalogues

abstract:
  VizieR is a database grouping in an homogeneous way thousands of astronomical
catalogues gathered since decades by the Centre de Donnees de Strasbourg (CDS)
and participating institutes. The history and current status of this large
collection is briefly presented, and the way these catalogues are being
standardized to fit in the VizieR system is described. The architecture of the
database is then presented, with emphasis on the management of links and of
accesses to very large catalogues. Several query interfaces are currently
available, making use of the ASU protocol, for browsing purposes or for use by
other data processing systems such as visualisation tools.


title:
Age and metallicity gradients in the Galactic Bulge - A differential
  study using HST/WFPC2

abstract:
  The Galactic Bulge has long been assumed to be a largely old stellar
population. However, some recent studies based on observations with the HST
WF/PC-1 and WFPC2 of stars in the Galactic Bulge have concluded that the old
population may not make up more then 30% of the total. Other studies using
HST/WFPC2 differential studies of `Bulge' globular clusters and field stars
have found the bulge to be comparable in age to the Galactic Halo. A
complication in all these studies is the presence of a substantial population
of stars which mimic a young bulge population, but which may be, and are often
assumed to be, foreground disk stars whose reddening and distance distributions
happen to mimic a young bulge turnoff. We show, using number counts in
HST/WFPC2 colour-magnitude diagrams of both field stars in the Bulge and of two
`bulge' and one `disk' globular cluster (NGC6528, NGC6553, and NGC5927) that
the stars interpreted as young in fact are foreground disk stars. Thus, we
confirm that the bulk of the bulge field stars in Baade's Window are old. The
existence of a young metal-rich population cannot, however, be ruled out from
our data. We also test for age and metallicity gradients using the CMD of a
metal-rich globular cluster as an empirical isochrone and derive a metallicity
difference of <0.2 dex between Baade's window and SGR-I window.


title: Fractal structures and the large scale distribution of galaxies

abstract:
  Galaxy structures are certainly fractal up to a certain crossover scale
\lambda_0. A clear determination of such a scale is still missing. Usually, the
conceptual and practical implications of this property are neglected and the
structures are only discussed in terms of their global amplitude. Here we
present a compact summary of these implications. First, we discuss the problem
of the identification of the crossover scale \lambda_0 and the proper
characterization of the scaling. We then consider the implications of these
properties with respect to various physical phenomena and to the corresponding
characteristic values, i.e. r_0, \sigma_8, \Omega, etc. These implications
crucially depend on the value of \lambda_0, but they are still important for a
relatively small value, say \lambda_0 \approx 50 \hmp. Finally we consider the
main theoretical consequences of these results.


title: The Lyman Continuum Polarization Rise in the QSO PG 1222+228

abstract:
  Some QSOs show an abrupt, strong rise in polarization near rest wavelength
750 A. If this arises in the atmosphere of an accretion disk around a
supermassive black hole, it may have diagnostic value. In PG 1222+228, the
polarization rise occurs at the wavelength of a sharp drop in flux. We examine
and reject interpretations of this feature involving a high velocity outflow.
The observations agree with a model involving several intervening Lyman limit
systems, two of which happen to coincide with the Lyman continuum polarization
rise. After correction for the Lyman limit absorption, the continuum shortward
of 912 A is consistent with a typical power-law slope, alpha = -1.8. This
violates the apparent pattern for the Lyman limit polarization rises to occur
only in ``candidate Lyman edge QSOs''. The corrected, polarized flux rises
strongly at the wavelength of the polarization rise, resembling the case of PG
1630+377. The rise in polarized flux places especially stringent requirements
on models.


title: Quintessence at Galactic Level?

abstract:
  Recently it has been proposed that the main contributor to the dark energy of
the Universe is a dynamical, slow evolving, spatially inhomogeneous scalar
field called quintessence. We investigate the behavior of this scalar field at
galactic level by assuming that it is the dark matter compossing the halos of
galaxies. Using an exact solution of the Einstein's equations we find an
excellent concordance between our results and observations.


title:
MeV-scale Reheating Temperature and Thermalization of Neutrino
  Background

abstract:
  The late-time entropy production by the massive particle decay induces the
various cosmological effects in the early epoch and modify the standard
scenario. We investigate the thermalization process of the neutrinos after the
entropy production by solving the Boltzmann equations numerically. We find that
if the large entropy are produced at t $\sim$ 1 sec, the neutrinos are not
thermalized very well and do not have the perfect Fermi-Dirac distribution.
Then the freeze-out value of the neutron to proton ratio is altered
considerably and the produced light elements, especially He4, are drastically
changed. Comparing with the observational light element abundances, we find
that $T_R$ < 0.7 MeV is excluded at 95 % C.L. We also study the case in which
the massive particle has a decay mode into hadrons. Then we find that $T_R$
should be a little higher, i.e. $T_R$ > 2.5 MeV - 4 MeV, for the hadronic
branching ratio $B_h = 10^{-2} - 1$. Possible influence of late-time entropy
production on the large scale structure formation and temperature anisotropies
of cosmic microwave background is studied. It is expected that the future
satellite experiments (MAP and PLANCK) to measure anisotropies of cosmic
microwave background radiation temperature can detect the vestige of the
late-time entropy production as a modification of the effective number of the
neutrino species $N_{\nu}^{\rm eff}$.


title: Eccentric Orbits of close Companions to Asymptotic Giant Branch Stars

abstract:
  I propose that the relatively high eccentricity found in some tidally
strongly interacting binary systems, where the mass-losing star is an evolved
giant star, e.g., an asymptotic giant branch star, is caused by an enhanced
mass loss rate during periastron passages. Tidal interaction by itself will
circularize the orbits of these systems in a relatively short time, hence a
mechanism which increases the eccentricity on a shorter time scale is required.
The proposed scenario predicts that the nebula formed by the mass loss process
possesses a prominent departure from axisymmetrical structure. Such a departure
is observed in the Red Rectangle, which has a central binary system, HD 44179,
with an orbital period of 318 days, and an eccentricity of e=0.38.


title:
Multi-frequency VLBI observations of faint gigahertz peaked spectrum
  sources

abstract:
  We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of
a sample of faint Gigahertz Peaked Spectrum (GPS) sources selected from the
Westerbork Northern Sky Survey (WENSS). The 5 GHz observations involved a
global array of 16 stations and yielded data on the total sample of 47 sources.
A subsample of 26 GPS sources with peak frequencies > 5 GHz and/or peak flux
densities > 125 mJy was observed with the VLBA at 15 GHz. A second subsample of
29 sources, with peak frequencies <5 GHz, was observed at 1.6 GHz using a 14
station global VLBI array. In this way, 44 of the 47 sources (94%) in the
sample were observed above and at or below their spectral peak. Spectral
decomposition allowed us to identify 3, 11, 7, and 2 objects as compact
symmetric objects, compact doubles, core-jet and complex sources respectively.
  However, many of the sources classified as compact double or core-jet sources
show only two components making their classification rather tentative. This may
explain why the strong morphological dichotomy of GPS quasars and galaxies
found for radio-bright GPS sources, is not as clear in this faint sample.


title: On the evolution of young radio-loud AGN

abstract:
  This paper describes an investigation of the early evolution of extragalactic
radio sources using samples of faint and bright Gigahertz Peaked Spectrum (GPS)
and Compact Steep Spectrum (CSS) radio galaxies. Correlations found between
their peak frequency, peak flux density and angular size provide strong
evidence that synchrotron self absorption is the cause of the spectral
turnovers, and indicate that young radio sources evolve in a self-similar way.
In addition, the data seem to suggest that the sources are in equipartition
while they evolve. If GPS sources evolve to large size radio sources, their
redshift dependent birth-functions should be the same. Therefore, since the
lifetimes of radio sources are thought to be short compared to the Hubble time,
the observed difference in redshift distribution between GPS and large size
sources must be due to a difference in slope of their luminosity functions. We
argue that this slope is strongly affected by the luminosity evolution of the
individual sources. A scenario for the luminosity evolution is proposed in
which GPS sources increase in luminosity and large scale radio sources decrease
in luminosity with time. This evolution scenario is expected for a ram-pressure
confined radio source in a surrounding medium with a King profile density. In
the inner parts of the King profile, the density of the medium is constant and
the radio source builds up its luminosity, but after it grows large enough the
density of th e surrounding medium declines and the luminosity of the radio
source decreases. A comparison of the local luminosity function (LLF) of GPS
galaxies with that of extended sources is a good test for this evolution
scenario [abridged].


title: Jet directions in Seyfert galaxies

abstract:
  We present the study of the relative angle between the accretion disk (or
radio jet) and the galaxy disk for a sample of Seyfert galaxies selected from a
mostly isotropic property, the 60$\mu$m flux. For each galaxy we have a pair of
points ($i$,$\delta$), which are the inclination of the galaxy relative to the
line of sight and the angle between the jet projected into the plane of the sky
and the host galaxy major axis, respectively. This data is combined with a
statistical technique to determine the distribution of $\beta$ angles {\it in 3
dimensions}, the angle between the jet and the host galaxy plane axis. The
analysis of the data, not differentiating between Seyfert 1's and 2's, showed
that the observed distribution of $i$ and $\delta$ values can be well
represented by a homogeneous $\beta-$distribution in the range
$0^{\circ}\leq\beta\leq90^{\circ}$. However, when we distinguished between
Seyfert 1's and 2's, the models could not represent Seyfert 1's adequately. It
was necessary to introduce viewing angle restrictions, that a galaxy can only
be recognized as a Seyfert 1 if the angle between the jet and the line of sight
($|\phi|$) is smaller than a given angle $\phi_c$ and that the galaxy
inclination $i$ is smaller than an angle $i_c$, in order to have statistically
acceptable models. This is a direct and independent confirmation of the
underlying concepts of the Unified Model. We discuss several ways to explain
the misalignment between the accretion disk axis and the host galaxy disk axis.


title: Jet directions in Seyfert galaxies: B and I imaging data

abstract:
  We present the results of broad-band B and I imaging observations for a
sample of 88 Seyfert galaxies (29 Seyfert 1's and 59 Seyfert 2's), selected
from a mostly isotropic property, the flux at 60$\mu$m. We also present the B
and I imaging results for an additional sample of 20 Seyfert galaxies (7
Seyfert 1's and 13 Seyfert 2's), selected from the literature and known to have
extended radio emission. The I band images are fitted with ellipses to
determine the position angle and ellipticity of the host galaxy major axis.
This information will be used in a future paper, combined with information from
radio observations, to study the orientation of radio jets relative to the
plane of their host galaxies (Kinney et al. 2000). Here we present surface
brightness profiles and magnitudes in the B and I bands, as well as mean
ellipticities and major axis position angles.


title: Models of Disk Evolution: Confrontation with Observations

abstract:
  We present simple models for disk evolution based on two different
approaches: a forward approach based on predictions generic to hierarchical
models for structure formation (e.g., Mo, Mao, & White 1998) and a backwards
approach based on detailed modeling of the Milky Way galaxy (e.g., Bouwens,
Cayon, & Silk 1997). We normalize these models to local observations and
predict high-redshift luminosities, sizes, circular velocities, and surface
brightnesses. Both approaches yield somewhat similar predictions for size,
surface brightness, and luminosity evolution though they clearly differ in the
amount of number evolution. These predictions seem to be broadly consistent
with the high-redshift observations of Simard et al. (1999), suggesting that
the B-band surface brightness of disks has indeed evolved by ~1.5 mag from z~0
to z~1 similar to the models and is not an artifact of selection effects as
previously claimed. We also find a lack of low surface brightness galaxies in
several high redshift samples relative to model predictions based on local
samples (de Jong & van der Kruit 1994; Mathewson, Ford, & Buchhorn 1992).


title:
Temporal and Spectral Variabilities of High Energy Emission from Blazars
  Using Synchrotron Self-Compton Models

abstract:
  Multiwavelength observations of blazars such as Mrk 421 and Mrk 501 show that
they exhibit strong short time variabilities in flare-like phenomena. Based on
the homogeneous synchrotron self-Compton (SSC) model and assuming that time
variability of the emission is initiated by changes in the injection of
nonthermal electrons, we perform detailed temporal and spectral studies of a
purely cooling plasma system. One important parameter is the total injected
energy E and we show how the synchrotron and Compton components respond as E
varies. We discuss in detail how one could infer important physical parameters
using the observed spectra. In particular, we could infer the size of the
emission region by looking for exponential decay in the light curves. We could
also test the basic assumption of SSC by measuring the difference in the rate
of peak energy changes of synchrotron and SSC peaks. We also show that the
trajectory in the photon-index and flux plane evolves clockwise or
counter-clockwise depending on the value of E and observed energy bands.


title: The Formation and Fragmentation of Primordial Molecular Clouds

abstract:
  Many questions in physical cosmology regarding the thermal history of the
intergalactic medium, chemical enrichment, reionization, etc. are thought to be
intimately related to the nature and evolution of pregalactic structure. In
particular the efficiency of primordial star formation and the primordial IMF
are of special interest. We present results from high resolution
three--dimensional adaptive mesh refinement simulations that follow the
collapse of primordial molecular clouds and their subsequent fragmentation
within a cosmologically representative volume. Comoving scales from 128 kpc
down to 1 pc are followed accurately. Dark matter dynamics, hydrodynamics and
all relevant chemical and radiative processes (cooling) are followed
self-consistently for a cluster normalized CDM structure formation model.
Primordial molecular clouds with ~10^5 solar masses are assembled by mergers of
multiple objects that have formed hydrogen molecules in the gas phase with a
fractional abundance of ~10^-4. As the subclumps merge cooling lowers the
temperature to ~200 Kelvin in a `cold pocket' at the center of the halo. Within
this cold pocket, a quasi-hydrostatically contracting core with ~200 solar mass
and number densities > 10^5 cm^-3 is found. We find that less than 1% of the
primordial gas in such small scale structures cools and collapses to
sufficiently high densities to be available for primordial star formation.
Furthermore, it is worthwhile to note that this study achieved the highest
dynamic range covered by structured adaptive mesh techniques in cosmological
hydrodynamics to date.


title:
Cosmic Star Formation History Required from Infrared Galaxy Number Count
  : Future Prospect for Infrared Imaging Surveyor (IRIS)

abstract:
  We constructed a model of infrared and sub-mm (hereafter IR) galaxy number
count and estimated history of the IR luminosity density. We treat the
evolutionary change of galaxy luminosities as a stepwise nonparametric form, in
order to explore the most suitable evolutionary history which reproduces the
present observational results. We found the evolutionary patterns which satisfy
both constraints required from Cosmic Infrared Background (CIRB) and IR galaxy
number counts. One order of magnitude increase of luminosity at redshift
$z=0.75 - 1.0$ was found in IR $60 \mu$m luminosity density evolution. We also
found that a large number of galaxies ($\sim 10^7$ in the whole sky) will be
detected in all-sky survey at far-infrared by Infrared Imaging Surveyor (IRIS);
Japanese infrared satellite project Astro-F.


title:
Electron Acceleration and Time Variability of High Energy Emission from
  Blazars

abstract:
  Blazars are known to emit a broad band emission from radio to gamma-rays with
rapid time variations, particularly, in X- and gamma-rays. Synchrotron
radiation and inverse Compton scattering are thought to play an important role
in emission and the time variations are likely related to the acceleration of
nonthermal electrons. As simultaneous multiwavelength observations with
continuous time spans are recently available, some characteristics of electron
acceleration are possibly inferred from the spectral changes of high energy
emission. In order to make such inferences, we solve the time-dependent kinetic
equations of electrons and photons simultaneously using a simple model for
electron acceleration. We then show how the time variations of emission are
dependent on electron acceleration. We also present a simple model for a flare
in X-rays and TeV gamma-rays by temporarily changing the acceleration
timescale. Our model will be used, in future, to analyze observed data in
detail to obtain information on electron acceleration in blazars.


title:
Discovery of high proper motion ancient white dwarfs: nearby massive
  compact halo objects?

abstract:
  We present the discovery and spectroscopic identification of two very high
proper motion ancient white dwarf stars, found in a systematic proper motion
survey. Their kinematics and apparent magnitude clearly indicate that they are
halo members, while their optical spectra are almost identical to the recently
identified cool Halo white dwarf WD0346+246. Canonical stellar halo models
predict a white dwarf volume density of two orders of magnitude less than the
approx 7*10^{-4} Solar masses per pc^{-3} inferred from this survey. With the
caveat that the sample size is very small, it appears that a significant
fraction, about 10%, of the local dark matter halo is in the form of very old,
cool, white dwarfs.