title: The Blazar Main Sequence

abstract:
  We propose a sequence (the Blazar main sequence, BMS) that links the two main
components of the Blazar class, namely, the Flat Spectrum Radio Quasars and the
BL Lacertae objects, and yields all their distinctive features in a correlated
way. In this view, both type of sources are centered on a supermassive Kerr
hole close to maximal spin that produces a relativistic jet observed close to
the axis, and on the associated accretion disk that emits more isotropically.
But the FSRQs are energized by accretion at rates dm/dt ~ 1, and are dominated
by the disk components (thermal and electrodynamic jet-like component) which
provide outputs in excess of L ~ 10^46 erg/s. On the other hand, accretion
levels dm/dt << 1 are enough to energize the BL Lacs; here the radiation is
highly non-thermal and the power partly contributed by the rotational energy of
the central Kerr hole, with the latter and the disk together sustaining L ~
10^44 erg/s in the jet frame for several Gyrs. If so, we expect the BL Lacs to
show quite different evolutionary signatures from the FSRQs, and in particular,
number counts close to the Euclidean shape, or flatter if the sources make a
transition to the BL Lac from a FSRQ mode. In addition, for lower dm/dt along
the BMS, we expect the large scale electric fields to be less screened out, and
to accelerate fewer particles to higher energies with non-thermal radiations at
higher frequencies; so in moving from FSRQs to BL Lacs these non-thermal
radiations will peak at frequencies inversely correlated with the disk output.
For the BL Lacs such dependence implies increased scatter when one tries a
correlation with the total ouput. At its endpoint, the BMS suggests widespread
objects that are radiatively silent, but still efficient in accelerating cosmic
rays to ultra high energies.


title:
Spin Clustering of Accreting X-ray Neutron Stars as Possible Evidence of
  Quark Matter

abstract:
  A neutron star in binary orbit with a low-mass non-degenerate companion
becomes a source of x-rays with millisecond variability when mass accretion
spins it up. Centrifugally driven changes in density profile may initiate a
phase transition in a growing region of the core parallel to what may take
place in an isolated millisecond pulsar, but in reverse. Such a star will spend
a longer time in the spin frequency range over which the transition occurs than
elsewhere because the change of phase, paced by the spinup rate, is accompanied
by a growth in the moment of inertia. The population of accreters will exhibit
a clustering in the critical frequency range. A phase change triggered by
changing spin and the accompanying adjustment of moment of inertia has its
analogue in rotating nuclei.


title:
Chandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M
  106)

abstract:
  This paper presents high resolution X-ray observations with Chandra of NGC
4258 and infers the nature of the so called ``anomalous arms'' in this galaxy.
The anomalous arms dominate the X-ray image; diffuse X-ray emission from the
``plateaux'' regions, seen in radio and H$\alpha$ imaging, is also found. X-ray
spectra have been obtained at various locations along the anomalous arms and
are well described by thermal (mekal) models with kT in the range 0.37 - 0.6
keV. The previously known kpc-scale radio jets are surrounded by cocoons of hot
X-ray emitting gas for the first 350 pc of their length. The radio jets, seen
in previous VLBA and VLA observations, propagate perpendicular to the compact
nuclear gas disk (imaged in water vapor maser emission). The angle between the
jets and the rotation axis of the galactic disk is 60$^{\circ}$. The jets shock
the normal interstellar gas along the first 350 pc of their length, causing the
hot, X-ray emitting cocoons noted above. At a height of z = 175 pc from the
disk plane, the jets exit the normal gas disk and then propagate though the low
density halo until they reach ``hot spots'' (at 870 pc and 1.7 kpc from the
nucleus), which are seen in radio, optical line and X-ray emission. These jets
must drive mass motions into the low density halo gas. This high velocity halo
gas impacts on the dense galactic gas disk and shock heats it along and around
a ``line of damage'', which is the projection of the jets onto the galactic gas
disk as viewed down the galaxy disk rotation axis. However, because NGC 4258 is
highly inclined ($i$ = 64$^{\circ}$), the ``line of damage'' projects on the
sky in a different direction to the jets themselves. We calculate the expected
p.a. of the ``line of damage'' on the sky and find that it coincides with the
anomalous arms to within 2$^{\circ}$. (Abstract truncated).


title:
Fast, exact CMB power spectrum estimation for a certain class of
  observational strategies

abstract:
  We describe a class of observational strategies for probing the anisotropies
in the cosmic microwave background (CMB) where the instrument scans on rings
which can be combined into an n-torus, the {\em ring torus}. This class has the
remarkable property that it allows exact maximum likelihood power spectrum
estimation in of order $N^2$ operations (if the size of the data set is $N$)
under circumstances which would previously have made this analysis intractable:
correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes,
non-uniform distribution of integration time on the sky and partial sky
coverage. This ease of computation gives us an important theoretical tool for
understanding the impact of instrumental effects on CMB observables and hence
for the design and analysis of the CMB observations of the future. There are
members of this class which closely approximate the MAP and Planck satellite
missions. We present a numerical example where we apply our ring torus methods
to a simulated data set from a CMB mission covering a 20 degree patch on the
sky to compute the maximum likelihood estimate of the power spectrum $C_\ell$
with unprecedented efficiency.


title: Is the Compact Source at the Center of Cas A Pulsed?

abstract:
  A 50 ksec observation of the Supernova Remnant Cas A was taken using the
Chandra X-Ray Observatory High Resolution Camera (HRC) to search for periodic
signals from the compact source located near the center. Using the HRC-S in
imaging mode, problems with correctly assigning times to events were overcome,
allowing the period search to be extended to higher frequencies than possible
with previous observations. In an extensive analysis of the HRC data, several
possible candidate signals are found using various algorithms, including
advanced techniques developed by Ransom to search for low significance periodic
signals. Of the candidate periods, none is at a high enough confidence level to
be particularly favored over the rest. When combined with other information,
however (e.g., spectra, total energetics, and the historical age of the
remnant), a 12 ms candidate period seems to be more physically plausible than
the others, and we use it for illustrative purposes in discussing the possible
properties of a putative neutron star in the remnant. We emphasize that this is
not necessarily the true period, and that a follow-up observation, scheduled
for the fall of 2001, is required.
  A 50 ksec Advanced CCD Imaging Spectrometer (ACIS) observation was taken, and
analysis of these data for the central object shows that the spectrum is
consistent with several forms, and that the emitted X-ray luminosity in the 0.1
-10 keV band is 10^{33}-10^{35}erg cm^{-2}sec^{-1} depending on the spectral
model and the interstellar absorption along the line of sight to the source.


title: A close view on the protoplanetary disk in the Bok globule CB26

abstract:
  We present new sub-arcsecond-resolution near-infrared polarimetric imaging
and millimetre interferometry data on the circumstellar disk system in the Bok
globule CB26. The data imply the presence of a M > 0.01 M_sun edge-on disk of
>400 AU in diameter, being in Keplerian rotation around a young ~0.35 M_sun
star. The mm dust emission from the inner 200 AU is highly optically thick, but
the outer parts are optically thin and made of small dust grains. Planetesimal
growth in the inner disk could neither be comfirmed nor excluded. The outer
optically thin part of the disk is strongly warped. We argue that the CB 26
disk is a very young protoplanetary disk and show that it is comparable to the
early solar system.


title:
First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to
  Constrain the Plasma Density of a Cosmic X-ray Source

abstract:
  We show that the Fe XVII I(17.10 A)/I(17.05 A) line ratio observed in the
Chandra HETG spectrum of the intermediate polar EX Hydrae is significantly
smaller than that observed in the Sun or other late-type stars. Using the
Livermore X-ray Spectral Synthesizer, which calculates spectral models of
highly charged ions based on HULLAC atomic data, we find that the observed
I(17.10 A)/I(17.05 A) line ratio can be explained if the plasma density n_e >
3x10^{14} cm^{-3}. However, if photoexcitation is included in the level
population kinetics, the line ratio can be explained for any density if the
photoexcitation temperature T_bb > 55 kK. For photoexcitation to dominate the
Fe XVII level population kinetics, the relative size of the hotspot on the
white dwarf surface must be f < 2%. This constraint and the observed X-ray flux
requires a density n > 2x10^{14} cm^{-3} for the post-shock flow. Either way,
then, the Chandra HETG spectrum of EX Hya requires a plasma density which is
orders of magnitude greater than that observed in the Sun or other late-type
stars.


title:
A Composite Seyfert 2 X-ray Spectrum: Implications for the Origin of the
  Cosmic X-ray Background

abstract:
  We present a composite 1-10 keV Seyfert 2 X-ray spectrum, derived from ASCA
observations of a distance-limited sample of nearby galaxies. All 29 observed
objects were detected. Above ~3 keV, the composite spectrum is inverted,
confirming that Seyfert 2 galaxies as a class have the spectral properties
necessary to explain the flat shape of the cosmic X-ray background spectrum.
Integrating the composite spectrum over redshift, we find that the total
emission from Seyfert 2 galaxies, combined with the expected contribution from
unabsorbed type 1 objects, provides an excellent match to the spectrum and
intensity of the hard X-ray background. The principal uncertainty in this
procedure is the cosmic evolution of the Seyfert 2 X-ray luminosity function.
Separate composite spectra for objects in our sample with and without polarized
broad optical emission lines are also presented.


title: Lyman Continuum Extinction by Dust in H {\sc ii} Regions of Galaxies

abstract:
  We examine Lyman continuum extinction (LCE) in H II regions by comparing
infrared fluxes of 49 H II regions in the Galaxy, M31, M33, and the LMC with
estimated production rates of Lyman continuum photons. A typical fraction of
Lyman continuum photons that contribute to hydrogen ionization in the H II
regions of three spiral galaxies is $\la$ 50 %. The fraction may become smaller
as the metallicity (or dust-to-gas ratio) increases. We examine the LCE effect
on estimated star formation rates (SFR) of galaxies. The correction factor for
the Galactic dust-to-gas ratio is 2-5.


title: Collisional Evolution of Galaxy Clusters and the Growth of Common Halos

abstract:
  We investigated the dynamical evolution of clusters of galaxies in virial
equilibrium using Fokker-Planck models and self-consistent N-body models. In
particular, we focused on the growth of a common halo, which is a cluster-wide
halo formed by matter stripped from galaxies, and the development of a central
density cusp. The Fokker-Planck models include the effects of two-body
gravitational encounters both between galaxies and between galaxies and common
halo particles. The effects of tidal mass stripping from the galaxies due to
close galaxy-galaxy encounters and accompanying dissipation of the orbital
kinetic energies of the galaxies were also taken into account in the
Fokker-Planck models. We find that the results of the Fokker-Planck models are
in excellent agreement with those of the N-body models regarding the growth of
the common halo mass and the evolution of the cluster density profiles. In the
central region of the cluster, a shallow density cusp, approximated by $\rho
(r) \propto r^{-\alpha}$ ($\alpha \sim$ 1), develops. This shallow cusp results
from the combined effects of two-body relaxation and tidal stripping. The cusp
steepness, $\alpha$, weakly depends on the relative importance of the tidal
stripping. When the effect of stripping is important, the central velocity
dispersion decreases as the central density increases and, consequently, a
shallow ($\alpha <2$) cusp is formed. In the limit of no stripping, usual
gravothermal core collapse occurs, i.e. the central velocity dispersion
increases as the central density increases with a steep ($\alpha >2$) cusp
left. We conclude from our consideration of the origin of the cusp demonstrated
here that shallow cusps should develop in real galaxy clusters.


title:
The Parkes Multibeam Pulsar Survey: I. Observing and Data Analysis
  Systems, Discovery and Timing of 100 Pulsars

abstract:
  The Parkes multibeam pulsar survey is a sensitive survey of a strip along the
Galactic plane with |b|<5 deg and l=260 deg to l=50 deg. It uses a 13-beam
receiver on the 64-m Parkes radio telescope, receiving two polarisations per
beam over a 288 MHz bandwidth centred on 1374 MHz. Receiver and data
acquisition systems are described in some detail. For pulsar periods in the
range 0.1 - 2 s and dispersion measures of less than 300 cm^{-3} pc, the
nominal limiting flux density of the survey is about 0.2 mJy. At shorter or
longer periods or higher dispersions, the sensitivity is reduced. Timing
observations are carried out for pulsars discovered in the survey for 12 - 18
months after confirmation to obtain accurate positions, spin parameters,
dispersion measures, pulse shapes and mean flux densities. The survey is
proving to be extremely successful, with more than 600 pulsars discovered so
far. We expect that, when complete, this one survey will come close to finding
as many pulsars as all previous pulsar surveys put together. The newly
discovered pulsars tend to be young, distant and of high radio luminosity. They
will form a valuable sample for studies of pulsar emission properties, the
Galactic distribution and evolution of pulsars, and as probes of interstellar
medium properties. This paper reports the timing and pulse shape parameters for
the first 100 pulsars timed at Parkes, including three pulsars with periods of
less than 100 ms which are members of binary systems. These results are briefly
compared with the parameters of the previously known population.


title: Formation of the Galactic stellar halo I. Structure and kinematics

abstract:
  We perform numerical simulations for the formation of the Galactic stellar
halo, based on the currently favored cold dark matter (CDM) theory of galaxy
formation. Our numerical models, taking into account both dynamical and
chemical evolution processes in a consistent manner, are aimed at explaining
observed structure and kinematics of the stellar halo in the context of
hierarchical galaxy formation. The main results of the present simulations are
summarized as follows. (1) Basic physical processes involved in the formation
of the stellar halo, composed of metal-deficient stars with [Fe/H] $\le$ -1.0,
are described by both dissipative and dissipationless merging of subgalactic
clumps and their resultant tidal disruption in the course of gravitational
contraction of the Galaxy at high redshift ($z$ $>$ 1). (2) The simulated halo
has the density profile similar to the observed power-law form of $\rho (r)$
$\sim$ $r^{-3.5}$, and has also the similar metallicity distribution to the
observations. The halo virtually shows no radial gradient for stellar ages and
only small gradient for metallicities. (3) The dual nature of the halo, i.e.,
its inner flattened and outer spherical density distribution, is reproduced, at
least qualitatively, by the present model. The outer spherical halo is formed
via essentially dissipationless merging of small subgalactic clumps, whereas
the inner flattened one is formed via three different mechanisms, i.e.,
dissipative merging between larger, more massive clumps, adiabatic contraction
due to the growing Galactic disk, and gaseous accretion onto the equatorial
plane.


title: Turbulence-driven angular momentum transport in modulated Kepler flows

abstract:
  The velocity fluctuations in a spherical shell arising from sinusoidal
perturbations of a Keplerian shear flow with a free amplitude parameter
\epsilon are studied numerically by means of fully 3D nonlinear simulations.
The investigations are performed at high Reynolds numbers, i.e.
  3000 < Re < 5000. We find Taylor-Proudman columns of large eddies parallel to
the rotation axis for sufficiently strong perturbations. An instability sets in
at critical amplitudes with \epsilon_crit \propto Re^-1. The whole flow turns
out to be almost axisymmetric and nonturbulent exhibiting, however, a very rich
radial and latitudinal structure. The Reynolds stress <u'_r u'_\phi> is
positive in the entire computational domain, from its Gaussian radial profile a
positive viscosity-alpha of about 10^-4 is derived. The kinetic energy of the
turbulent state is dominated by the azimuthal component <u_\phi'^2> whereas the
other components are smaller by two orders of magnitude. Our simulations
reveal, however, that these structures disappear as soon as the perturbations
are switched off. We did not find an ``effective'' perturbation whose amplitude
is such that the disturbance is sustained for large times (cf. Dauchot &
Daviaud 1995) which is due to the effective violation of the Rayleigh stability
criterion. The fluctuations rapidly smooth the original profile towards to pure
Kepler flow which, therefore, proves to be stable in that sense.


title: VLT spectroscopy of XTE J2123-058 during quiescence

abstract:
  We present VLT low resolution spectroscopy of the neutron star X-ray
transient XTE J2123-058 during its quiescent state. Our data reveal the
presence of a K7V companion which contributes 77 % to the total flux at 6300 A
and orbits the neutron star at K_2 = 287 +/- 12 km/s. Contrary to other soft
X-ray transients (SXTs), the Halpha emission is almost exactly in antiphase
with the velocity curve of the optical companion. Using the light-center
technique we obtain K_1 = 140 +/- 27 km/s and hence q=K_1/K_2=M_2/M_1= 0.49 +/-
0.10. This, combined with a previous determination of the inclination angle
(i=73 +/- 4) yields M_1 = 1.55 +/- 0.31 Msun and M_2 = 0.76 +/- 0.22 Msun. M_2
agrees well with the observed spectral type. Doppler tomography of the Halpha
emission shows a non-symmetric accretion disc distribution mimicking that seen
in SW Sex stars. Although we find a large systemic velocity of -110 +/- 8 km/s
this value is consistent with the galactic rotation velocity at the position of
J2123-058, and hence a halo origin. The formation scenario of J2123-058 is
still unresolved.


title:
The contribution of galaxies to the UV ionising background and the
  evolution of the Lyman forest

abstract:
  We have modelled the evolution of the number of Ly_alpha absorbers with
redshift, resulting from the evolution of the ionising background and the
Hubble expansion. The contribution of quasars (QSOs) and galaxies to the
HI-ionising UV background has been estimated. The QSOs emissivity is derived
from recent fits of their luminosity function. The galaxy emissivity is
computed using a stellar population synthesis model, with a star-formation
history scaled on observations of faint galaxies at lambda <= 1500 A. We allow
for three values of the fraction of ionising photons that can escape the
interstellar medium, f_esc=0.05, 0.1 and 0.4. The Intergalactic Medium is
modelled as made of purely-absorbing clouds with the distribution in redshift
and column density obtained from QSOs absorption lines. For the adopted values
of f_esc, the contribution of galaxies to the ionising UV background is
comparable or greater than that of QSOs. Accounting for the contribution of
clouds to the UV emission, all models with f_esc <~ 0.1 provide an ionising
flux compatible with local and high-z determination, including those with a
pure QSOs background. The observed z ~ 1 break in the evolution can be better
explained by a dominant contribution from galaxies. We find that models in
Lambda-cosmology with Omega_matter=0.3, Omega_Lambda=0.7 describe the flat
absorbers evolution for z <~ 1.0 better than models for Omega_matter=1.0.


title:
Jet launching theory and the vertical structure of a
  magnetically-dominated thin accretion disc

abstract:
  The presence of an imposed external magnetic field may drastically influence
the structure of thin accretion discs. The magnetic field energy is here
assumed to be in balance with the thermal energy of the accretion flow. The
vertical magnetic field, its toroidal component B^tor at the disc surface (due
to different rotation rates between disc and its magnetosphere), the turbulent
magnetic Prandtl number and the viscosity-alpha are the key parameters of our
model. Inside the corotation radius for rather small B^tor the resulting
inclination angle i of the magnetic field lines to the disc surface normal can
exceed the critical value 30^\circ (required to launch cold jets) even for
small magnetic Prandtl numbers of order unity. The self-consistent
consideration of both magnetic field and accretion flow demonstrates a weak
dependence of the inclination (``dragging'') angle on the magnetic Prandtl
number for given surface density but a strong dependence on the toroidal field
component at the disc surface.
  A magnetic disc is thicker than a nonmagnetic one for typical parameter
values. The accretion rate can be strongly amplified by large B^tor and small
magnetic Prandtl number. On the other hand, for given accretion rate the
magnetised disc is less massive than the standard-alpha disc. The surface
values of the toroidal magnetic fields which are necessary to induce
considerably high values for the inclination angle are much smaller than
expected and are of order 10^-3 of the imposed vertical field. As the innermost
part of the disc produces the largest B^tor, the largest radial inclination can
be expected also there. The idea is therefore supported that the cold jets are
launched only in the central disc area.


title:
A search for gamma-ray emission from the Galactic plane in the longitude
  range between 37 deg and 43 deg

abstract:
  Using the HEGRA system of imaging atmospheric Cherenkov telescopes, a region
of the Galactic plane (-10 deg < b < 5 deg, 38 deg < l < 43 deg) was surveyed
for TeV gamma-ray emission, both from point sources and of diffuse nature. The
region covered includes 15 known pulsars, 6 known supernova remnants (SNR) and
one unidentified EGRET source. No evidence for emission from point sources was
detected; upper limits are typically below 0.1 Crab units for the flux above 1
TeV. For the diffuse gamma-ray flux from the Galactic plane, an upper limit of
6.1*10E-15 ph/(cm2 s sr MeV) was derived under the assumption that the spatial
distribution measured by the EGRET instrument extends to the TeV regime. This
upper flux limit is a factor of about 1.5 larger than the flux expected from
the ensemble of gamma-ray unresolved Galactic cosmic ray sources.


title:
Long-Slit Observations of Extended C II 1335 Emission Around V854
  Centauri and RY Sagittarii

abstract:
  We have obtained long-slit far-ultraviolet (1150--1730 A) spectra of the R
Coronae Borealis (RCB) stars V854 Cen and RY Sgr, near maximum light and
pulsational phase zero, with the Space Telescope Imaging Spectrograph (STIS) on
Hubble Space Telescope (HST). The far-UV spectrum of each star shows a
photospheric continuum rising steeply toward longer wavelengths, and a
prominent emission feature at C II 1335. RY Sgr displays a second, but fainter,
emission attributed to Cl I 1351 (which is radiatively fluoresced by C II
1335), but Cl I is weak or absent in V854 Cen. Most surprisingly, the C II
emission of V854 Cen is significantly extended along the slit by +/- 2.5
arcsec, about 6 x 10^3 AU at the distance of the star. The C II feature of RY
Sgr exhibits no such gross extension. Nevertheless, subtle broadenings of the C
II emissions beyond the point response profile suggests inner clouds of radius
\~0.1 arcsec (250 AU) around both stars. V854 Cen is only the third RCB star
after R CrB and UW Cen known to have a resolved shell.


title: High Energy Hadronic Acceleration in Extragalactic Radio Jets

abstract:
  Within an electric circuit description of extragalactic jets temporal
variations of the electric currents are associated with finite collisionless
conductivities and consequently magnetic-field aligned electric fields
$E_\parallel$. The maximum field strengths depend on the efficiency of the jet
MHD generator $E_\perp$ and the local conversion to the $E_\parallel$
component. The hadronic jet constituents can efficiently be accelerated in such
fields all along the jets. To estimate the maximum energy the accelerated jet
hadrons can achieve we consider energy loss processes as photon-pion and pair
production as well as synchrotron and inverse Compton radiation. It turns out
that for the strongest $E_\parallel$ possible the Centaurus A jet is a most
promising candidate for the source of the highest energy component of cosmic
rays.


title: Relative space-time transformations in GRBs

abstract:
  The GRB 991216 and its relevant data acquired from the BATSE experiment and
RXTE and Chandra satellites are used as a prototypical case to test the theory
linking the origin of gamma ray bursts (GRBs) to the process of vacuum
polarization occurring during the formation phase of a black hole endowed with
electromagnetic structure (EMBH). The relative space-time transformation
paradigm (RSTT paradigm) is presented. It relates the observed signals of GRBs
to their past light cones, defining the events on the worldline of the source
essential for the interpretation of the data. Since GRBs present regimes with
unprecedently large Lorentz $\gamma$ factor, also sharply varying with time,
particular attention is given to the constitutive equations relating the four
time variables: the comoving time, the laboratory time, the arrival time at the
detector, duly corrected by the cosmological effects. This paradigm is at the
very foundation of any possible interpretation of the data of GRBs.


title: On the interpretation of the burst structure of GRBs

abstract:
  Given the very accurate data from the BATSE experiment and RXTE and Chandra
satellites, we use the GRB 991216 as a prototypical case to test the EMBH
theory linking the origin of the energy of GRBs to the electromagnetic energy
of black holes. The fit of the afterglow fixes the only two free parameters of
the model and leads to a new paradigm for the interpretation of the burst
structure, the IBS paradigm. It leads as well to a reconsideration of the
relative roles of the afterglow and burst in GRBs by defining two new phases in
this complex phenomenon: a) the injector phase, giving rise to the proper-GRB
(P-GRB), and b) the beam-target phase, giving rise to the extended afterglow
peak emission (E-APE) and to the afterglow. Such differentiation leads to a
natural possible explanation of the bimodal distribution of GRBs observed by
BATSE. The agreement with the observational data in regions extending from the
horizon of the EMBH all the way out to the distant observer confirms the
uniqueness of the model.


title: SED Signatures of Jovian Planets Around White Dwarf Stars

abstract:
  The problem of detecting Jovian-sized planets orbiting White Dwarf stars is
considered. Significant IR excesses result from warm Jupiters orbiting a White
Dwarf of $T_{\rm eff}=10000$ K at a distance of $\sim 10^3$ White Dwarf radii
(corresponding to $\sim 10^2$ Jupiter radii or a few tenths of an AU) with an
orbital period of $\sim 100$ days. Such a planet will have a 10 micron flux
density at its Wien peak that is comparable to the emission of the White Dwarf
at that wavelength. Although the White Dwarf is much hotter than the planet,
the planet will have peak brightness at the IR, well into the Rayleigh-Jeans
tail of the White Dwarf, plus Jovians are about 10 times larger than White
Dwarfs, so there is a substantial gain in the planet to star brightness
contrast as compared to planets around Main Sequence stars. In the solar
neighborhood, there are 51 White Dwarf stars within 13 pc of the Sun. At 10 pc,
the IR flux density of ``warm'' Jupiters (a few hundred Kelvin) will fall in
the range 10--100 micro-Jansky which should be observable with {\it SIRTF}.


title: On a possible GRB-supernova time sequence

abstract:
  The data from the Chandra satellite on the iron emission lines in the
afterglow of GRB 991216 are used to give further support for the EMBH theory,
which links the origin of the energy of GRBs to the extractable energy of
electromagnetic black holes (EMBHs), leading to an interpretation of the
GRB-supernova correlation. Following the relative space-time transformation
(RSTT) paradigm and the interpretation of the burst structure (IBS) paradigm,
we introduce a paradigm for the correlation between GRBs and supernovae. The
following sequence of events is shown as kinematically possible and consistent
with the available data: a) the GRB-progenitor star $P_1$ first collapses to an
EMBH, b) the proper GRB (P-GRB) and the peak of the afterglow (E-APE) propagate
in interstellar space until the impact on a supernova-progenitor star $P_2$ at
a distance $\le 2.69\times 10^{17}$ cm, and they induce the supernova
explosion, c) the accelerated baryonic matter (ABM) pulse, originating the
afterglow, reaches the supernova remnants 18.5 hours after the supernova
explosion and gives rise to the iron emission lines. Some considerations on the
dynamical implementation of the paradigm are presented. The concept of induced
supernova explosion introduced here specifically for the GRB-supernova
correlation may have more general application in relativistic astrophysics.


title:
On the physical processes which lie at the bases of time variability of
  GRBs

abstract:
  The relative-space-time-transformation (RSTT) paradigm and the interpretation
of the burst-structure (IBS) paradigm are applied to probe the origin of the
time variability of GRBs. Again GRB 991216 is used as a prototypical case,
thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is
found that with the exception of the relatively inconspicuous but
scientifically very important signal originating from the initial ``proper
gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be
explained by the interaction of the accelerated-baryonic-matter pulse with
inhomogeneities in the interstellar matter. This can be demonstrated by using
the RSTT paradigm as well as the IBS paradigm, to trace a typical spike
observed in arrival time back to the corresponding one in the laboratory time.
Using these paradigms, the identification of the physical nature of the time
variablity of the GRBs can be made most convincingly. It is made explicit the
dependence of a) the intensities of the afterglow, b) the spikes amplitude and
c) the actual time structure on the Lorentz gamma factor of the
accelerated-baryonic-matter pulse. In principle it is possible to read off from
the spike structure the detailed density contrast of the interstellar medium in
the host galaxy, even at very high redshift.


title: Analysis of CMB polarization on an incomplete sky

abstract:
  The full sky cosmic microwave background polarization field can be decomposed
into 'electric' and 'magnetic' components. Working in harmonic space we
construct window functions that allow clean separation of the electric and
magnetic modes from observations over only a portion of the sky. Our
construction is exact for azimuthally symmetric patches, but should continue to
perform well for arbitrary patches. From the window functions we obtain
variables that allow for robust estimation of the magnetic component without
risk of contamination from the probably much larger electric signal. For
isotropic, uncorrelated noise the variables have a very simple diagonal noise
correlation, and further analysis using them should be no harder than analysing
the temperature field. For an azimuthally-symmetric patch, such as that
obtained from survey missions when the galactic region is removed, the
exactly-separated variables are fast to compute allowing us to estimate the
magnetic signal that could be detected by the Planck satellite in the absence
of non-galactic foregrounds. We also discuss the sensitivity of future
experiments to tensor modes in the presence of a magnetic signal generated by
weak lensing, and give lossless methods for analysing the electric polarization
field in the case that the magnetic component is negligible.


title:
Late-type stars members of young stellar kinematic groups - I. Single
  stars

abstract:
  This is the first paper of a series aimed at studying the properties of
late-type stars members of young stellar kinematic groups. We concentrate our
study on classical young moving groups as: Local Association (Pleiades moving
group, 20 - 150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius
supercluster, 300 Myr), and Hyades supercluster (600 Myr); as well as on
recently identified groups as: Castor moving group (200 Myr). In this paper we
have compiled a preliminary list of single late-type stars possible members of
some of these young stellar kinematic groups. Stars have been selected from
previously established members of stellar kinematic groups based on photometric
and kinematic properties as well as from candidates based on other criteria as
their level of chromospheric activity, rotation rate, lithium abundance.
Precise measurements of proper motions and parallaxes taken from Hipparcos
Catalogue, as well as from Tycho-2 Catalogue, and published radial velocity
measurements are used to calculate the Galactic space motions (U, V, W) and to
apply the Eggen's kinematic criteria in order to determine the membership of
the selected stars to the different groups. Additional criteria using
age-dating methods for late-type stars will be applied in forthcoming papers of
this series. A further study of the list of stars compiled here could lead to a
better understanding of the chromospheric activity and their age evolution as
well as of the star formation history in the solar neighbourhood. In addition,
these stars are also potential search targets for direct imaging detection of
sub-stellar companions.


title:
Studying the anisotropy of the gravitational wave stochastic background
  with LISA

abstract:
  A plethora of gravitational wave stochastic backgrounds populate the
sensitivity window of the Laser Interferometer Space Antenna. We show that LISA
can detect the anisotropy of the background corresponding to the multipole
moments of order l=2 and 4. The signal-to-noise ratio generated by galactic
white dwarf binary systems could be as high as 60 for 3 yrs of integration, and
LISA could provide valuable information on the spatial distribution of a
variety of galactic sources. We also show that the cross-correlation of the
data sets from two interferometers could marginally lead to meaningful
upper-limits on the degree of isotropy of the primordial gravitational wave
background.


title:
An Adaptive Grid, Implicit Code for Spherically Symmetric, General
  Relativistic Hydrodynamics in Comoving Coordinates

abstract:
  We describe an implicit general relativistic hydrodynamics code. The
evolution equations are formulated in comoving coordinates. A conservative
finite differencing of the Einstein equations is outlined, and artificial
viscosity and numerical diffusion are discussed. The time integration is
performed with AGILE, an implicit solver for stiff algebrodifferential
equations on a dynamical adaptive grid. We extend the adaptive grid technique,
known from nonrelativistic hydrodynamics, to the general relativistic
application and identify it with the concept of shift vectors in a 3+1
decomposition. The adaptive grid minimizes the number of required computational
zones without compromising the resolution in physically important regions.
Thus, the computational effort is greatly reduced when the zones are subject to
computationally expensive additional processes, such as Boltzmann radiation
transport or a nuclear reaction network. We present accurate results in the
standard tests for supernova simulations: Sedov's point-blast explosion, the
nonrelativistic and relativistic shock tube, the Oppenheimer-Snyder dust
collapse, and homologous collapse.


title: Dark Matter or a New Force?

abstract:
  We show that a new force, which appeared in a five-dimensional generalization
of general relativity, implies precisely the flat circular velocity curves of
luminous matter observed in the outer parts of spiral galaxies. A cosmological
solution for the new force (not the galactic solution treated in this paper)
might explain the cosmic negative, or repulsive, gravitation responsible for
the accelerated expansion of the universe, attributed nowadays to ``dark
energy'' and sometimes modelled by Einstein's cosmological constant.


title: Formation of Twin Clusters in a Galactic Tidal Field

abstract:
  The formation of globular clusters is still an unsolved problem. Though most
scenarios assume a massive molecular cloud as the progenitor, it is unclear,
how the cloud is transformed into a star cluster. Here a scheme of supernova
(SN) induced cluster formation is investigated. In this scenario the expanding
SN shell accumulates the mass of the cloud. This is accompanied by
fragmentation resulting in star formation in the shell. If this stellar shell
expands sufficiently slow, its self-gravity leads to a recollapsing shell, by
this forming one or several stellar clusters.
  In this paper N-body simulations of collapsing shells moving on circular
orbits in a galactic potential are presented. It is shown that typical shells
(10^5 Msun, 30 pc) evolve to twin clusters in the galactocentric distance range
between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside
5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin
cluster contains about 55% of the shell's mass, whereas the mass of the smaller
decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end
up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only
fragments substantially less massive than the initial shell survive.


title: The Structure of Dark Matter Halos in an Annihilating Dark Matter Model

abstract:
  The inability of standard non-interacting cold dark matter (CDM) to account
for the small scale structure of individual galaxies has led to the suggestion
that the dark matter may undergo elastic and/or inelastic scattering. We
simulate the evolution of an isolated dark matter halo which undergoes both
scattering and annihilation. Annihilations produce a core that grows with time
due to adiabatic expansion of the core as the relativistic annihilation
products flow out of the core, lessening the binding energy. An effective
annihilation cross section per unit mass equal to $>.03 cm^2 g^{-1} (100 km
s^{-1}/v$) with a scattering cross section per unit mass of .6 cm g$^{-1}$
produces a 3 kpc core in a 10$^{10}$ M$_{\sun}$ halo that persists for 100
dynamical times. The same cross section leads to a core of only 120 pc in a
rich cluster. In addition to creating to cores, annihilation should erase
structure on scales below $\sim 3\times10^8$ M$_{\sun}$. Annihilating dark
matter provides a mechanism for solving some of the problems of non-interacting
CDM, at the expense of introducing a contrived particle physics model.


title:
The Polatron: A Millimeter-Wave Cosmic Microwave Background Polarimeter
  for the OVRO 5.5 m Telescope

abstract:
  We describe the development of a bolometric receiver designed to measure the
arcminute-scale polarization of the cosmic microwave background (CMB). The
Polatron will be mounted at the Cassegrain focus of the 5.5 m telescope at the
Owens Valley Radio Observatory (OVRO). The receiver will measure both the Q and
U Stokes parameters over a 20% pass-band centered near 100 GHz, with the input
polarization signal modulated at ~0.6 Hz by a rotating, birefringent, quartz
half-wave plate. In six months of observation we plan to observe ~400 2.5
arcminute pixels in a ring about the North Celestial Pole to a precision of ~6
\mu K/pixel in each of Q and U, adequate to unambiguously detect CMB
polarization at levels predicted by current models.


title: Polarization Properties of Nine Southern Radio Pulsars

abstract:
  We report on radio polarimetry observations for nine southern pulsars. Six of
the nine in the sample are young, with characteristic ages under 100 kyr and
high spin-down luminosities. All six show a significant degree of linear
polarization. We also confirm a previously noticed trend in which the degree of
linear polarization increases with spin-down luminosity. Where possible we have
used the rotating-vector model of the pulsar emission geometry to fit the
observed position angle data. Our fit for PSR J1513-5908 (B1509-58) in
particular is useful for directly testing the magnetospheric model of Melatos
(1997) in combination with further timing observations. For this pulsar we find
that a magnetic inclination angle greater than or equal to 60 degrees is
excluded at the 3-sigma level, and that the geometry suggested by the
morphology of an apparent bipolar X-ray outflow is marginally inconsistent with
the Melatos model. We also report on polarimetry of three older pulsars: PSR
J0045-7319, PSR J1627-4845, and PSR J1316-6232 (whose discovery we also
report). Of these, only PSR J0045-7319 shows significant polarization.


title: Dynamical Evolution of Triplets of Galaxies

abstract:
  By means of N-body simulations we study the global dynamics of triplets of
galaxies, considering initial conditions starting from `maximum expansion' and
in virial equilibrium. Unlike previous studies we treat galaxies
self-consistently. We do not consider the influence of a primordial common halo
of dark matter. Our results indicate that a low number of triple mergers are
expected at the present epoch (~10%) for collapsing triplets. Initially
virialised conditions yield ~5% of triple mergers in ~10 Gyr of evolution;
hence, the 3-galaxy problem has stable states. No overmerging problem for these
small groups of galaxies is found. Their geometrical properties, as reflected
by the Agekyan-Anosova map, do not show an excess of extreme hierarchical
triplets. The median velocity dispersion of observed compact triplets (~100
km/s) is not well reproduced in our models at the present epoch. However, about
10% of simulated triplets starting from maximum expansion have dynamical
properties very similar to them. Our median values agree, however, very well
with new data on triples. We find that the median mass estimators performs
somewhat better than the virial mass estimate. The VME underestimates mass by
\~35%. We conclude that Karachentsev's compact triplets probably represent the
most advanced stage of gravitational clustering of initially diffuse triplets.


title: HST UV and Keck HIRES Spectra of BAL Quasars

abstract:
  In the analysis of broad absorption line (BAL) quasar spectra, Keck HIRES
spectra are a useful complement to lower resolution HST and ground based
spectra. The HIRES spectra provide accurate parameters for narrow, intervening
type absorption systems including Lyman limit systems and a direct measurement
of the smoothness of BAL features. The smoothness of the troughs is related to
the number of "clouds" in the BAL region if the BAL region consists of clouds.
The HIRES spectra, especially for z approx. 2 quasars, are also a source of
high quality absorption templates. All of the BAL features are apparently
resolved in the high resolution spectra (R approx. 45 000), while low
resolution (R approx. 1000) spectra do not always resolve features belonging to
the outflow.


title: On the Dynamic Stability of Cool Supergiant Atmospheres

abstract:
  We have developed a new formalism to compute the thermodynamic coefficient
Gamma1 in the theory of stellar and atmospheric stability. We generalize the
classical derivation of the first adiabatic index, which is based on the
assumption of thermal ionization and equilibrium between gas and radiation
temperature, towards an expression which incorporates photo-ionization due to
radiation with a temperature T_rad different from the local kinetic gas
temperature.Our formalism considers the important non-LTE conditions in the
extended atmospheres of supergiant stars. An application to the Kurucz grid of
cool supergiant atmospheres demonstrates that models with T_rad =~ T_eff
between 6500 K and 7500 K become most unstable against dynamic perturbations,
according to Ledoux' stability integral <Gamma1>. This results from Gamma1 and
<Gamma1> acquiring very low values, below 4/3, throughout the entire stellar
atmosphere, which causes very high gas compression ratios around these
effective temperatures. Based on detailed NLTE-calculations, we discuss
atmospheric instability of pulsating massive yellow supergiants, like the
hypergiant rho Cas (Ia+), which exist in the extension of the Cepheid
instability strip, near the Eddington luminosity limit.


title:
Spatially Resolved STIS Spectroscopy of alpha Orionis: Evidence for
  Non-radial Chromospheric Oscillation from Detailed Modeling

abstract:
  Four spatially resolved near-UV raster scans across the chromospheric disk of
alpha Ori, obtained with the Space Telescope Imaging Spectrograph on the Hubble
Space Telescope, reveal mean chromospheric infall from 1998 January to 1998
April, which reversed to upflow in deeper layers between 1998 September and
1999 March. In 1998 September we detect systematic reversals in the component
maxima of four double-peaked emission lines of Si I (UV 1), Fe II (UV 36), Fe
II (UV 61), and Al II] (UV 1), when scanning across the UV disk. Detailed
modeling of the Si I lambda 2516 resonance line with radiative transport
calculations in spherical geometry constrain the mean radial velocity structure
in the projected slit area (25 by 100 mas) for different aperture positions,
observed off-limb to 157.5 mas. Hence we determine with semi-empirical models
that these spatial reversals of emission line components correspond with
average opposite flow velocities of ~2 km/s across the chromospheric disk. We
determine that the chromospheric velocity field can not be represented by a
unique radial velocity structure across the stellar disk in order to match the
observed peak ratios of this raster scan. These sub-sonic velocities indicate
(local) non-radial movements of chromospheric fluid in confined regions during
a chromospheric oscillation phase, which reverses from global contraction into
expansion over this monitoring period of 15 months.


title: Cosmological Parameter Determination from Counts of Galaxies

abstract:
  We study constraints that anticipated DEEP survey galaxy counts versus
redshift data will place on cosmological model parameters in models with and
without a constant or time-variable cosmological constant $\Lambda$. This data
will result in fairly tight constraints on these parameters. For example, if
all other parameters of a spatially-flat model with a constant $\Lambda$ are
known, the galaxy counts data should constrain the nonrelativistic matter
density parameter $\Omega_0$ to about 5% (10%, 1.5%) at 1 $\sigma$ with neutral
(worst case, best case) assumptions about data quality.


title: Extended Quintessence and its Late-time Domination

abstract:
  Various astronomical observations point towards the evidence for dark energy.
One of the most mysterious problem is the coincidence problem: why dark energy
becomes dominant only recently. We present a scenario based on extended
quintessence models to explain the late-time domination of dark energy without
severe fine-tuning of initial conditions and model parameters.


title: Constraining Lambda using cluster quadrupoles

abstract:
  We examine how the statistics of the quadrupoles of (projected) cluster
masses can discriminate between flat cold dark matter (CDM) universes with or
without a cosmological constant term. Even in the era of high precision
cosmology that cosmic microwave background experiments should open soon, it is
important to devise self consistency tests of cosmogonic theories tuned at the
matter radiation decoupling epoch using data from the non--linear evolved
universe. We build cluster catalogs from two large volume simulations of a
``tilted'' CDM model and a $\Lambda$CDM model with cosmic density parameter
$\Omega_m=0.35$ and cosmological constant contribution $\Omega_\Lambda=0.65$.
  From the projected mass distribution of the clusters we work out the
quadrupoles Q and examine their dependence on cluster mass and the cosmological
model. We find that TCDM clusters have systematically larger quadrupoles than
their \lcdm counterpart. The effect is mass dependent: massive clusters
($M\gsim 10^{15}\Msunh$) have quadrupoles differing by more than 30% in the two
models, while for $M\lsim 4\times10^{14}\Msunh$ the difference rapidly drops to
$\sim 1$%. Performing a K-S test of the Q distributions, we estimate that using
just the 15 most massive clusters in the simulation volume ($360\Mpch$ a side)
we can discriminate between TCDM and \lcdm at a confidence level better than
99.9%. In the volume probed by exhisting observations, there are potentially
several hundred clusters with masses above the threshold for which the
differences in the quadrupoles become relevant. Should weak lensing data become
available for this whole set, a quadrupole analysis may be expected to
discriminate among different values of $\Lambda$.


title: Is the gas in cooling-flows multi-phase?

abstract:
  Employing XMM-Newton EPIC data we perform a detailed comparison between
different spectral models to test whether the gas in cooling-flows is
multi-phase or not. Our findings all point in the same direction, namely that
gas in cooling-flows does not show the wide distribution of temperatures
expected from standard multi-phase models. This result has profound
implications for cooling-flow models. Firstly, the large absorption column
depths inferred by previous analysis of cooling-flow spectra are most likely an
artifact following from the application of an incorrect spectral model to the
data. Secondly, the mass deposition and mass flow are likely to be much smaller
than previously thought. Last, but perhaps not least, the term "cooling-flow"
cluster is probably no longer appropriate, as it describes a phenomenon of
smaller entity and impact than previously thought. We propose to substitute it
with that of "cool-core" cluster. The latter definition is less ambitious than
the first, as it reflects only an observational fact rather than an inferred
physical property, the flow, but has the undeniable advantage of being firmer.


title: On the metal abundance in the core of M87

abstract:
  We revisit the XMM-Newton observation of M87 to make a new and more detailed
measurement of the metal abundance profile. After having verified that spectral
fits with single temperature models show a dramatic abundance drop within 1
arcmin of the cluster core, we show that more appropriate models, which include
a multi-temperature component to account for the strong temperature gradient
observed in M87, and a power-law component to account for the emission of the
nucleus and knot A, give a substantially flat abundance profile. The drastic
abundance decrement found by fitting a single temperature component to the data
is an artifact known as "Fe-bias" (Buote 2000a,b) following from the
application of an oversimplified spectral model to the data.


title:
Horizontal-Branch Models and the Second-Parameter Effect. IV. The Case
  of M3 and Palomar 3

abstract:
  We present a detailed analysis of the "second-parameter pair" of globular
clusters M3 (NGC 5272) and Palomar 3. Our main results can be summarized as
follows: i) The horizontal-branch (HB) morphology of M3 is significantly bluer
in its inner regions (observed with the Hubble Space Telescope) than in the
cluster outskirts (observed from the ground), i.e., M3 has an internal second
parameter. Most plausibly the mass loss on the red giant branch (RGB) has been
more efficient in the inner than in the outer regions of the cluster. ii) The
dispersion in mass of the Pal 3 HB is found to be very small -- consistent with
zero -- and we argue that this is unlikely to be due to a statistical
fluctuation. It is this small mass dispersion that leads to the most apparent
difference in the HB morphologies of M3 and Pal 3. iii) The relative HB types
of M3 and Pal 3, as measured by mean colors or parameters involving the number
of blue, variable, and red HB stars, can easily be accounted for by a fairly
small difference in age between these clusters, of order 0.5-1 Gyr -- which is
in good agreement with the relative age measurement, based on the clusters'
turnoffs, by VandenBerg (2000).


title:
Calculating exclusion limits for Weakly Interacting Massive Particle
  direct detection experiments without background subtraction

abstract:
  Competitive limits on the weakly interacting massive particle (WIMP)
spin-independent scattering cross section are currently being produced by 76Ge
detectors originally designed to search for neutrinoless double beta decay,
such as the Heidelberg-Moscow and IGEX experiments. In the absence of
background subtraction, limits on the WIMP interaction cross section are set by
calculating the upper confidence limit on the theoretical event rate, given the
observed event rate. The standard analysis technique involves calculating the
90% upper confidence limit on the number of events in each bin, and excluding
any set of parameters (WIMP mass and cross-section) which produces a
theoretical event rate for any bin which exceeds the 90% upper confidence limit
on the event rate for that bin. We show that, if there is more than one energy
bin, this produces exclusion limits that are actually at a lower degree of
confidence than 90%, and are hence erroneously tight. We formulate criteria
which produce true 90% confidence exclusion limits in these circumstances,
including calculating the individual bin confidence limit for which the overall
probability that no bins exceeds this confidence limit is 90% and calculating
the 90% minimum confidence limit on the number of bins which exceed their
individual bin 90% confidence limits. We then compare the limits on the WIMP
cross-section produced by these criteria with those found using the standard
technique, using data from the Heidelberg-Moscow and IGEX experiments.


title:
The Influence of Stellar Wind Variability on Measurements of
  Interstellar O VI Along Sightlines to Early-Type Stars

abstract:
  A primary goal of the FUSE mission is to understand the origin of the O VI
ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along
sightlines to OB-type stars, these interstellar components are usually blended
with O VI stellar wind profiles, which frequently vary in shape. In order to
assess the effects of this time-dependent blending on measurements of the
interstellar O VI lines, we have undertaken a mini-survey of repeated
observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud.
These sparse time series, which consist of 2-3 observations separated by
intervals ranging from a few days to several months, show that wind variability
occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does
in other resonance lines. However, in the interstellar O VI $\lambda$1032
region, the O VI $\lambda$1038 wind varies only in $\sim$30% of the cases. By
examining cases exhibiting large amplitude variations, we conclude that
stellar-wind variability {\em generally} introduces negligible uncertainty for
single interstellar O VI components along Galactic lines of sight, but can
result in substantial errors in measurements of broader components or blends of
components like those typically observed toward stars in the Large Magellanic
Cloud. Due to possible contamination by discrete absorption components in the
stellar O VI line, stars with terminal velocities greater than or equal to the
doublet separation (1654 km/s) should be treated with care.


title: Search for non-helical disc dynamos in simulations

abstract:
  The possibility of non-helical large scale dynamo action is investigated
using three-dimensional simulations of global accretion discs as well as
idealized local simulations without rotation and only shear. Particular
emphasis is placed on a certain correlation between vorticity and azimuthal
velocity gradient which has been predicted to drive large scale dynamo action,
independent of the presence or absence of kinetic helicity. In the global disc
simulations two types of behaviours are found: those which do show this type of
velocity correlation and those which do not. The former ones are typically also
the cases where the resistivity is larger. The latter ones show signs typical
of dynamo action based on the usual helicity effect. In the idealized
simulations without rotation and just shear the above correlation is found to
be particularly strong. In both cases there is, as expected, a systematic flux
of magnetic helicity through the midplane. However, very little helicity flux
leaves the domain through the top and bottom boundaries. The idealized
simulations reveal that much of this systematic flux comes from the rotational
component of the helicity flux and does not contribute to its divergence.


title: Modified Newtonian dynamics and its implications

abstract:
  Milgrom has proposed that the appearance of discrepancies between the
Newtonian dynamical mass and the directly observable mass in astronomical
systems could be due to a breakdown of Newtonian dynamics in the limit of low
accelerations rather than the presence of unseen matter. Milgrom's hypothesis,
modified Newtonian dynamics or MOND, has been remarkably successful in
explaining systematic properties of spiral and elliptical galaxies and
predicting in detail the observed rotation curves of spiral galaxies with only
one additional parameter-- a critical acceleration which is on the order of the
cosmologically interesting value of $cH_o$. Here I review the empirical
successes of this idea and discuss its possible extention to cosmology and
structure formation.


title: Evolution of galaxy clusters in $\Lambda$MDM cosmologies

abstract:
  The time evolution of galaxy cluster abundance is used to constrain
cosmological parameters in dark matter models containing a fraction of hot
particles (massive neutrino). We test the modified MDM models with cosmic
gravitational waves which are in agreement with observational data at $z=0$,
and show that they do not pass the cluster evolution test and therefore should
be ruled out. The models with a non-zero cosmological constant are in better
agreement with the evolution test. We estimate $\Omega_\Lambda$ and find that
it is strongly affected by a small fraction of hot dark matter: $0.4
<\Omega_\Lambda <0.8$ for $\Omega_H /\Omega_M <0.2$.


title:
Stationary components of HeI in strong magnetic fields - a tool to
  identify magnetic DB white dwarfs

abstract:
  In only three of the 61 known magnetic white dwarfs helium has been
identified unambiguously while about 20% of all non-magnetic stars of this
class are known to contain HeI or HeII. Until recently, data for HeI data were
available only for magnetic fields below 20MG. This changed with the
publication of extensive data by the group in Heidelberg. The corresponding
calculations have now been completed for the energetically lowest five states
of singlet and triplet symmetry for the subspaces with |m| <= 3; selected
calculations have been performed for even higher excitations. In strongly
magnetized white dwarfs only line components are visible whose wavelengths vary
slowly with respect to the magnetic field, particularly stationary components
which have a wavelength minimum or maximum in the range of the magnetic fields
strengths on the stellar surface. In view of the many ongoing surveys finding
white dwarfs we want to provide the astronomical community with a tool to
identify helium in white dwarfs for fields up to 5.3GG. To this end we present
all calculated helium line components whose wavelengths in the UV, optical, and
near IR vary slowly enough with respect to the field strength to produce
visible absorption features. We also list all stationary line components in
this spectral range. Finally, we find series of minima and maxima which occur
as a result of series of extremal transitions to increasingly higher
excitations. We estimated the limits for 8 series which can possibly give rise
to additional absorption in white dwarf spectra; one strong absorption feature
in GD229 which is yet unexplained by stationary components is very close to two
estimated series limits.


title:
Particle Acceleration in three dimensional Reconnection Regions: A New
  Test Particle Approach

abstract:
  Magnetic Reconnection is an efficient and fast acceleration mechanism by
means of direct electric field acceleration parallel to the magnetic field.
Thus, acceleration of particles in reconnection regions is a very important
topic in plasma astrophysics. This paper shows that the conventional analytical
models and numerical test particle investigations can be misleading concerning
the energy distribution of the accelerated particles, since they oversimplify
the electric field structure by the assumption that the field is homogeneous.
These investigations of the acceleration of charged test particles are extended
by considering three-dimensional field configurations characterized by
localized field-aligned electric fields. Moreover, effects of radiative losses
are discussed. The comparison between homogeneous and inhomogeneous electric
field acceleration in reconnection regions shows dramatic differences
concerning both, the maximum particle energy and the form of the energy
distribution.


title:
Acoustic instabilities at the transition from the radiation-dominated to
  the matter-dominated universe

abstract:
  The transition from acoustic noise in the radiation-dominated universe to the
density structures in the matter dominated epoch is considered. The initial
state is a stochastic field of sound waves moving in different directions. The
construction of the initial state is compatible with the hyperbolic type of
propagation equation for density perturbations, and parallel to the theory of
stochastic background of gravitational waves. Instantaneous transition between
the cosmological epochs is assumed, and Darmois-Israel joining conditions are
applied to match solutions for sound waves with growing or decaying modes at
the decoupling. As a result a substantial amplification of the low scale
structures is obtained.


title:
The Tolman Surface Brightness Test for the Reality of the Expansion.
  III. HST Profile and Surface Brightness Data for Early-Type Galaxies in Three
  High-Redshift Clusters

abstract:
  Photometric data for 34 early-type galaxies in the three high-redshift
clusters Cl 1324+3011 (z = 0.76), Cl 1604+4304 (z = 0.90), and Cl 1604+4321 (z
= 0.92), observed with the Hubble Space Telescope (HST) and with the Keck
10-meter telescopes by Oke, Postman & Lubin, are analyzed to obtain the
photometric parameters of mean surface brightness, magnitudes for the growth
curves, and angular radii at various Petrosian eta radii. The angular radii at
eta = 1.3 mag for the program galaxies are all larger than 0.24". All of the
galaxies are well resolved at this angular size using HST whose point-spread
function is 0.05", half width at half maximum. The data for each of the program
galaxies are listed at eta = 1.0, 1.3, 1.5, 1.7, and 2.0 mag. They are
corrected by color equations and K terms for the effects of redshift to the
rest-frame Cape/Cousins I for Cl 1324+3011 and Cl 1604+4304 and R for Cl
1604+4321. The K corrections are calculated from synthetic spectral energy
distributions derived from evolving stellar population models of Bruzual &
Charlot which have been fitted to the observed broad-band (BVRI) AB magnitudes
of each program galaxy. The listed photometric data are independent of all
cosmological parameters. They are the source data for the Tolman surface
brightness test made in Paper IV.


title: Star formation time-scales in the nearby, prototype starburst galaxy M82

abstract:
  The last tidal encounter between M82 and M81, some 500 Myr ago, had a major
impact on what was probably an otherwise normal, quiescent disc galaxy. It
caused a concentrated burst of star formation in the form of massive star
clusters, which decreased rapidly, within a few 100 Myr. The current starburst
in the centre of the galaxy is likely either due to large-scale propagating
star formation or possibly related to late infall of tidally disrupted debris
from M82 itself. It may, in fact, be a combination of these two mechanisms, in
the sense that the star formation in the active core is actually propagating,
while the overall evolution of the starburst is due to tidal debris raining
back onto the disc of the galaxy, causing the present-day starburst.


title: Hard radio spectra from reconnection regions in galactic nuclei

abstract:
  Extremely flat and inverted radio spectra as observed in galactic nuclei and
BL Lac sources are still a challenge for fast particle acceleration models.
Continuous acceleration by electric fields in reconnection regions can result
in almost constant particle distributions and thereby in inverted synchrotron
spectra independent from the details of the injected spectrum. These spectra
are calculated from a spatially averaged diffusion transport equation in
momentum space that includes systematic momentum gains and losses as well as
finite particle escape lifetimes.


title:
The Tolman Surface Brightness Test for the Reality of the Expansion. IV.
  A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type
  Galaxies

abstract:
  We review a sample of the early literature in which the reality of the
expansion is discussed, explain Hubble's reticence to accept the expansion as
real, and contrast the Tolman surface brightness test with three other modern
tests. We search for the Tolman surface brightness depression with redshift
using the Hubble Space Telescope (HST) data from Paper III for 34 early-type
galaxies from the three clusters Cl 1324+3011 (z=0.76), Cl 1604+4304 (z=0.90),
and Cl 1604+4321 (z=0.92). Depressions of the surface brightness relative to
the zero-redshift fiducial lines in the mean surface brightness, log linear
radius diagrams of Paper I are found for all three clusters. Expressed as the
exponent, n, in 2.5 log (1 + z)^n mag, the value of n for all three clusters is
n = 2.59 +/- 0.17 in the R band and 3.37 +/- 0.13 in the I band for a q_o = 1/2
model. The sensitivity of the result to the assumed value of q_o is shown to be
less than 23% between q_o = 0 and +1. For a true Tolman signal with n = 4, the
luminosity evolution in the look-back time, expressed as the exponent in 2.5
log (1+z)^(4-n) mag, must then be between 1.72 to 1.19 in the R band and 0.94
to 0.45 in the I band. We show that this is precisely the range expected from
the evolutionary models of Bruzual & Charlot. We conclude that the Tolman
surface brightness test is consistent with the reality of the expansion. We
have also used the high-redshift HST data to test the ``tired light''
speculation for a non-expansion model for the redshift. The HST data rule out
the ``tired light'' model at a significance level of better than 10 sigma.


title:
Secondary antiprotons and propagation of cosmic rays in the Galaxy and
  heliosphere

abstract:
  High-energy collisions of cosmic-ray nuclei with interstellar gas are
believed to be the mechanism producing the majority of cosmic ray antiprotons.
Due to the kinematics of the process they are created with a nonzero momentum;
the characteristic spectral shape with a maximum at ~2 GeV and a sharp decrease
towards lower energies makes antiprotons a unique probe of models for particle
propagation in the Galaxy and modulation in the heliosphere. On the other hand,
accurate calculation of the secondary antiproton flux provides a ``background''
for searches for exotic signals from the annihilation of supersymmetric
particles and primordial black hole evaporation. Recently new data with large
statistics on both low and high energy antiproton fluxes have become available
which allow such tests to be performed. We use our propagation code GALPROP to
calculate interstellar cosmic-ray propagation for a variety of models. We show
that there is no simple model capable of accurately describing the whole
variety of data: boron/carbon and sub-iron/iron ratios, spectra of protons,
helium, antiprotons, positrons, electrons, and diffuse gamma rays. We find that
only a model with a break in the diffusion coefficient plus convection can
reproduce measurements of cosmic-ray species, and the reproduction of primaries
(p, He) can be further improved by introducing a break in the primary injection
spectra. For our best-fit model we make predictions of proton and antiproton
fluxes near the Earth for different modulation levels and magnetic polarity
using a steady-state drift model of propagation in the heliosphere.


title:
Chandra X-Ray Point Sources, including Supernova 1979C, in the Spiral
  Galaxy M100

abstract:
  Six x-ray point sources, with luminosities of $4 \times 10^{38} - 2 \times
10^{39} \rm ergs s^{-1}$ in the 0.4--7 keV band, were detected in Chandra
observations of the spiral galaxy M100. One source is identified with supernova
SN 1979C and appears to have roughly constant x-ray flux for the period 16--20
years after the outburst. The x-ray spectrum is soft, as would be expected if
the x-ray emission is due to the interaction of supernova ejecta with
circumstellar matter. Most of the other sources are variable either within the
Chandra observation or when compared to archival data. None are coincident with
the peak of the radio emission at the nucleus. These sources have harder
spectra than the supernova and are likely x-ray binaries. M100 has more bright
x-ray sources than typical for spiral galaxies of its size. This is likely
related to active star formation occurring in the galaxy.


title:
Orbital Eccentricity Effects on the Stochastic Gravitational Wave
  Background from Coalescing Binary Neutron Stars

abstract:
  Unresolved coalescing binary neutron stars in the Galaxy and beyond produce a
stochastic gravitational wave background within the LISA frequency band, which
can be potentially dangerous for possible detection of fundamentally more
interesting relic cosmological backgrounds. Here we address the question what
effects the unavoidable eccentricity of orbits of these systems should have on
the properties of this backgrounds. In particularly, we examine starting from
which frequency one-year observations with LISA can be secure from
contamination by the noise produced by galactic binary neutron stars in
eccentric orbits. We come to the conclusion that harmonics from such binaries
do not contribute significantly above $\sim 10^{-3}$ Hz.


title: The dividing line between FR I and FR II radio--galaxies

abstract:
  In the radio - host galaxy optical luminosity plane FR I and FR II
radio-galaxies are clearly divided. Since the optical luminosity of an
elliptical galaxy is an indication of the mass of its central black hole, we
propose that the FR I - FR II dividing luminosity is a function of the mass of
the black hole powering the active nucleus. Furthermore, as the radio power
gives an estimate of the total kinetic power carried by the jet, the FR I - FR
II separation can be re-interpreted as occurring at a constant ratio between
the jet power and the black hole mass. There is also convincing evidence of a
correlation between the radio power and the luminosity in narrow emission
lines. As the latter results from photoionization by the radiation produced by
accretion, we can estimate the ionizing luminosity and find that the separation
luminosity can be also re-expressed as a constant accretion rate between
\~0.01-0.001 of the Eddington one. This possibly regulates the accretion mode
and the consequent presence and characteristics of nuclear outflows.


title: How Mira Variables Change Visual Light by a Thousand-fold

abstract:
  Mira variables change visual light by up to 8 magnitudes over their roughly
yearly cycle. Here we present a simple explanation for the extremely large
amplitudes of light curves of oxygen-rich Mira variables. Metallic oxides, such
as TiO, form throughout the stellar atmosphere as the star cools when
approaching minimum light. When this happens, the visual light can be almost
completely absorbed at large radii, extending the visual photosphere to nearly
twice its nominal size. At these large radii, temperatures can fall to
approximately 1400 K and essentially all of the star's radiation emerges in the
infrared. Since almost no optical light is emitted at these low temperatures,
Mira variables can decrease their visual light by more than a thousand-fold and
almost "disappear" to the human eye.


title: Disk Accretion at 10 Myr: Results from the TW Hydrae Association

abstract:
  We present an analysis of the accretion properties of the members of the TW
Hydrae association. The Halpha emission line profile provides explicit evidence
of an active accretion flow in 3 out of 23 observed members of the association;
we use radiative transfer models to derive approximate accretion rates for
these 3 objects. The resulting accretion rates for these 10 Myr-old stars
(<10^-9 Msun/yr) are well over an order of magnitude lower than typical values
in 1 Myr-old T Tauri stars. The small fraction of TW Hydrae association objects
still accreting (13%, compared with ~70% in 1 Myr-old regions like Taurus),
along with the very small accretion rates, points to significant disk evolution
over 10 Myr, providing an important constraint on the timescales for planet
formation.


title: Computational Asteroseismology

abstract:
  White dwarf asteroseismology offers the opportunity to probe the structure
and composition of stellar objects governed by relatively simple physical
principles. The observational requirements of asteroseismology have been
addressed by the development of the Whole Earth Telescope, but the analysis
procedures still need to be refined before this technique can yield the
complete physical insight that the data can provide. We have applied an
optimization method utilizing a genetic algorithm to the problem of fitting
white dwarf pulsation models to the observed frequencies of the most thoroughly
characterized helium-atmosphere pulsator, GD 358. The free parameters in this
initial study included the stellar mass, the effective temperature, the surface
helium layer mass, the core composition, and the internal chemical profile. For
many years, astronomers have promised that the study of pulsating white dwarfs
would ultimately lead to useful information about the physics of matter under
extreme conditions of temperature and pressure. The optimization approach
developed in this dissertation has allowed us to finally make good on that
promise by exploiting the sensitivity of our models to the core composition. We
empirically determine that the central oxygen abundance in GD 358 is 84 +/- 3
percent. We use this value to place a preliminary constraint on the
C12(alpha,gamma)O16 nuclear reaction cross-section of S_300 = 295 +/- 15 keV
barns. We find a thick helium layer solution for GD 358 that provides a better
match to the data than previous fits, and helps to resolve a problem with the
evolutionary connection between PG 1159 stars and DBVs. [abridged]


title: The Cosmic Gamma-Ray Bursts

abstract:
  Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today.
They are a playground of relativists and observers alike. They may teach us
about the death of stars and the birth of black holes, the physics in extreme
conditions, and help us probe star formation in the distant and obscured
universe. In this review we summarise some of the remarkable progress in this
field over the past few years. While the nature of the GRB progenitors is still
unsettled, it now appears likely that at least some bursts originate in
explosions of very massive stars, or at least occur in or near the regions of
massive star formation. The physics of the burst afterglows is reasonably well
understood, and has been tested and confirmed very well by the observations.
Bursts are found to be beamed, but with a broad range of jet opening angles;
the mean gamma-ray energies after the beaming corrections are ~ 10^51 erg.
Bursts are associated with faint <R> ~ 25 mag) galaxies at cosmological
redshifts, with <z> ~ 1. The host galaxies span a range of luminosities and
morphologies, but appear to be broadly typical for the normal, actively
star-forming galaxy populations at comparable redshifts and magnitudes. Some of
the challenges for the future include: the nature of the short bursts and
possibly other types of bursts and transients; use of GRBs to probe the
obscured star formation in the universe, and possibly as probes of the very
early universe; and their detection as sources of high-energy particles and
gravitational waves.


title: 2016+112: A Gravitationally Lensed Type-II Quasar

abstract:
  A single-screen model of the gravitational lens system 2016+112 is proposed,
that explains recent Hubble Space Telescope} (HST) infrared (NICMOS-F160W)
observations and new high-resolution European VLBI Network (EVN) 5-GHz radio
observations, presented in this paper. In particular, we find that a massive
`dark' structure at the lens position, previously suggested by X-ray, optical
and spectroscopic observations of the field around 2016+112, is not necessarily
required to accommodate the strong lensing constraints. A massive structure to
the north-west of the lens system, suggested from a weak-lensing analysis of
the field, is included in the model. The lensed source is an X-ray bright
active galaxy at z=3.273 with a central bright optical continuum core and
strong narrow emission lines, suggestive of a type-II quasar. The EVN 5-GHz
radio maps show a radio-jet structure with at least two compact subcomponents.
We propose that the diamond caustic crosses the counter-jet of the radio
source, so that part of the counter-jet, host galaxy and narrow-line emission
regions are quadruply imaged. The remainder of the radio source, including the
core, is doubly imaged. Our lens model predicts a very high magnification
(mu~300) at the bightness peaks of the inner two radio components of complex C.
If the jet exhibits relativistic velocities on micro-arsecond scales, it might
result in apparent hyperluminal motion. However, the lack of strong radio
variability and the peaked radio spectrum imply that these motions need not be
present in the source. Our model furthermore implies that the optical spectrum
of C' can only show features of the AGN and its host galaxy.


title:
Quantum Gravity and Astrophysics: The Microwave Background and Other
  Thermal Sources

abstract:
  The problem of formulating a fully consistent quantum gravity theory (QGT)
has not yet been solved. Even before we are able to work out the details of a
complete theory, however, we do know some important qualitative features to be
expected in any quantum theory. Fluctuations of the metric, for example, are
expected and are associated with fluctuations of the lightcone. Lightcone
fluctuations affect the arrival time of signals from distant sources in
potentially measurable ways, broadening the spectra. In this paper, we start
with a thermal spectrum and derive the form of spectral changes expected in a
wide class of QGTs. We apply these results, valid for any thermal spectrum, to
the cosmic microwave background (CMB). The CMB offers two advantages: (1)
deviations from a thermal spectrum are well constrained, and (2) the radiation
emanates from the most distant source of light, the surface of last scattering.
We use existing CMB data to derive an upper bound on the value of $\Delta t,$
the mean spread in arrival times due to metric fluctuations: ${\Delta t} < 2.1
\times 10^{-14}$ s at the 95% confidence limit. This limit applies to a wide
range of QGTs, and falsifies those predicting a larger spread in arrival times.
We find this limit rules out at least one QGT, the 5-dimensional theory in
which the "extra" dimension is flat. Tests of other models may also be
possible, depending on the results of calculations to predict values of \Delta
t,$ and also a second time scale, $\tau_c,$ the correlation time, which is the
characteristic time scale of the metric fluctuations. We show that stronger
limits on the value of $\Delta t,$ hence on lightcone fluctuations, can likely
be derived through observations of of higher-T sources, e.g., in the X-ray and
gamma-ray regimes.


title: Evidence for an accelerating wind as the broad-line region in NGC 3516

abstract:
  Spectroscopic data in wavelengths 900--3000A have been obtained in a low flux
state of the nucleus of the Seyfert 1 galaxy NGC 3516. The line profiles show P
Cygni characteristics, particularly in O VI 1032A, and are compared with data
from an earlier higher state. The profiles are suggestive of, and consistent
with, an accelerating wind driven by a disk continuum source, in which the
ionisation radii have changed. This scenario may apply to the formation of
other broad emission lines in AGN.


title:
Chandra Detection of X-ray Absorption Associated with a Damped Lyman
  Alpha System

abstract:
  We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with
the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray
absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers.
For PKS 1127-145, we detect absorption which, if associated with an intervening
z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption
is not at z_{abs}=0.312, then the metallicity is still constrained to be less
than 23% solar. The advantage of the X-ray measurement is that the derived
metallicity is insensitive to ionization, inclusion of an atom in a molecule,
or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is
consistent with the oxygen abundance of 30% solar derived from optical nebular
emission lines in a foreground galaxy at the redshift of the absorber.
  For Q1331+171 and Q 0054+144, only upper limits were obtained, although the
exposure times were intentionally short, since for these two objects we were
interested primarily in measuring flux levels to plan for future observations.
The imaging results are presented in a companion paper.


title:
Effects of Foreground Contamination on the Cosmic Microwave Background
  Anisotropy Measured by MAP

abstract:
  We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.


title:
A 1.2mm MAMBO/IRAM-30m Survey of Dust Emission from the Highest Redshift
  PSS Quasars

abstract:
  We report 250 GHz (1.2mm) observations of redshift > 3.8 quasars from the
Palomar Sky Survey (PSS) sample, using the Max-Planck Millimetre Bolometer
(MAMBO) array at the IRAM 30-metre telescope. Eighteen sources were detected
and upper limits were obtained for 44 with 3-sigma flux density limits in the
range 1.5-4 mJy. Adopting typical dust temperatures of 40-50K, we derive dust
masses of ~10^8-10^9 M_sun and far-infrared luminosities of order 10^13 L_sun.
We suggest that a substantial fraction of this luminosity arises from young
stars, implying star formation rates approaching 10^3 M_sun/yr or more. The
high millimetre detection rate supports current views on a connection between
AGN and star forming activity, suggesting a parallel evolution of the central
black hole and of the stellar core of a galaxy, although their growth-rate
ratio seems higher than the mass ratio observed in nearby galaxies. The
observed, exceptionally bright objects may trace the peaks of the primordial
density field, the cores of future giant ellipticals


title:
H2 and CO emission from disks around TTauri and HerbigAe
  pre-main-sequence stars and from debris disks around young stars: warm and
  cold circumstellar gas

abstract:
  We present ISO-SWS observations of H2 pure-rotational line emission from the
disks around low and intermediate mass pre-main-sequence stars as well as from
young stars thought to be surrounded by debris disks. We detect `warm' (T ~
100-200 K) H2 gas around many sources, including tentatively the debris-disk
objects. The mass of this warm gas ranges from ~1E-4 Solar mass up to 8E-3
Solar mass, and can constitute a non-negligible fraction of the total disk
mass. Complementary single-dish 12CO 3-2, 13CO 3-2 and 12CO 6-5 observations
have been obtained as well. These transitions probe cooler gas at T ~ 20-80 K.
Most objects show a double-peaked CO emission profile characteristic of a disk
in Keplerian rotation, consistent with interferometer data on the lower-J
lines. The ratios of the 12CO 3-2/ 13CO 3-2 integrated fluxes indicate that
12CO 3-2 is optically thick but that 13CO 3-2 is optically thin or at most
moderately thick. The 13CO 3-2 lines have been used to estimate the cold gas
mass. If a H2/CO conversion factor of 1E4 is adopted, the derived cold gas
masses are factors of 10-200 lower than those deduced from 1.3 millimeter dust
emission assuming a gas/dust ratio of 100,in accordance with previous studies.
The warm gas is typically 1-10 % of the total mass deduced from millimeter
continuum emission, but can increase up to 100% or more for the debris-disk
objects. Thus, residual molecular gas may persist into the debris-disk phase.
No significant evolution in the H2, CO or dust masses is found for stars with
ages in the range of 1E6-1E7 years, although a decrease is found for the older
debris-disk star beta Pictoris. Existing models fail to explain the amount of
warm gas quantitatively.


title: Gravitational radiation from a torus around a black hole

abstract:
  Long gamma-ray bursts (GRBs) from rapidly spinning black hole-torus systems
may represent hypernovae or black hole-neutron star coalescence. We show that
the torus may radiate gravitational radiation powered by the spin-energy of the
black hole in the presence of non-axisymmetries. The coupling to the
spin-energy of the black hole is due to equivalence in poloidal topology to
pulsar magnetospheres. Results calculated in the suspended accretion state
indicate that GRBs are potentially the most powerful LIGO/VIRGO burst-sources
in the Universe, with an expected duration of 10-15s on a horizontal branch of
1-2kHz in the $\dot{f}(f)-$diagram.


title: Simulations of Clusters of Galaxies

abstract:
  Numerical simulations of clusters of galaxies provide a unique way to follow
the dynamics of these systems. The models reveal many characteristics of the
merging process of subclusters: shock structure and strength, temperature
distribution and gas distribution. From the models detailed observational
signatures of the dynamical state can be derived. The simulations also show
that mergers have effects on the magnetic field, on the X-ray luminosity, on
the metal enrichment and other physical processes. Furthermore, observational
methods like the mass determination can be tested.


title: Theory of GRB Afterglow

abstract:
  The most interesting current open question in the theory of GRB afterglow is
the propagation of jetted afterglows during the sideway expansion phase. Recent
numerical simulations show hydrodynamic behavior that differs from the one
suggested by simple analytic models. Still, somewhat surprisingly, the
calculated light curves show a `jet break' at about the expected time. These
results suggest that the expected rate of orphan optical afterglows should be
smaller than previously estimated.


title: Keck Spectroscopy of Dwarf Elliptical Galaxies in the Virgo Cluster

abstract:
  Keck spectroscopy is presented for four dwarf elliptical galaxies in the
Virgo Cluster. At this distance, the mean velocity and velocity dispersion are
well resolved as a function of radius between 100 to 1000 pc, allowing a clear
separation between nuclear and surrounding galaxy light. We find a variety of
dispersion profiles for the inner regions of these objects, and show that none
of these galaxies is rotationally flattened.


title:
Mean-pairwise peculiar velocity in cosmological N-body simulations:
  time-variation, scale-dependence and stable condition

abstract:
  We report on the detailed analysis of the mean-pairwise peculiar velocity
profile in high-resolution cosmological N-body simulations ($N=8.8\times 10^6$
particles in a sphere of $50 \sim 200$Mpc radius). In particular we examine the
validity and limitations of the stable condition which states that the mean
{\it physical} separation of particle pairs is constant on small scales. We
find a significant time-variation (irregular oscillatory behavior) of the
mean-pairwise peculiar velocity in nonlinear regimes. We argue that this
behavior is not due to any numerical artifact, but a natural consequence of the
continuous merging processes in the hierarchical clustering universe. While
such a time-variation is significant in a relatively local patch of the
universe, the global average over a huge spatial volume $\simgt$(200Mpc)$^3$
does not reveal any {\it systematic} departure from the stable condition. Thus
we conclude that the mean-pairwise peculiar velocity is rather unstable
statistics but still satisfies the stable condition when averaged over the
cosmological volume.


title: Galaxy Deconstruction: Clues from Globular Clusters

abstract:
  The present-day globular cluster populations of galaxies reflect the
cumulative effects of billions of years of galaxy evolution via such processes
as mergers, tidal stripping, accretion, and in some cases the partial or even
complete destruction of other galaxies. If large galaxies have grown by
consuming their smaller neighbors, or by accreting material stripped from other
galaxies, then their observed globular cluster systems are an amalgamation of
the globular cluster systems of their progenitors. Careful analysis of the
globular cluster populations of galaxies can thus allow astronomers to
reconstruct their dynamical histories.


title:
A Limit on the Large Angular Scale Polarization of the Cosmic Microwave
  Background

abstract:
  We present an upper limit on the polarization of the Cosmic Microwave
Background at 7 degree angular scales in the frequency band between 26 and 36
GHz, produced by the POLAR experiment. The campaign produced a map of linear
polarization over the R.A. range 112 degrees - 275 degrees at declination
43degrees. The model-independent upper limit on the E-mode polarization
component of the CMB at angular scales l = 2 - 20 is 10 microKelvin (95%
confidence). The corresponding limit for the B-mode is also 10 microKelvin.
Constraining the B-mode power to be zero, the 95% confidence limit on E-mode
power alone is 8 microKelvin.


title: X-ray Bursts from the Source A1742-294 in the Galactic-Center Region

abstract:
  We present results of observations of the X-ray burster A1742-294 near the
Galactic center with the ART-P telescope onboard the Granat observatory. The
shape of its persistent spectra was well described by the model of
bremsstrahlung from optically thin plasma, and it had remained essentially
unchanged over $\sim2.5$ years of observations. We show that the mean interval
between X-ray bursts from the source is several times shorter than assumed
previously, and that the burst profile itself depends on the flux during the
burst. We analyze in detail the strong X-ray burst detected from this source on
October 18, 1990, and trace the evolution of its luminosity and radiation
temperature.


title: Dynamics of gravitational clustering I. Building perturbative expansions

abstract:
  We develop a systematic method to obtain the solution of the collisionless
Boltzmann equation which describes the growth of large-scale structures as a
perturbative series over the initial density perturbations. We give an explicit
calculation of the second-order terms which are shown to agree with the results
obtained from the hydrodynamical description of the system. Then, we explain
that this identity extends to all orders of perturbation theory and that the
perturbative series actually diverge for hierarchical scenarios. However, since
the collisionless Boltzmann equation provides the exact description of the
dynamics (including the non-linear regime) these results may serve as a basis
for a study of the non-linear regime. In particular, we derive a
non-perturbative quadratic integral equation which explicitly relates the
actual non-linear distribution function to the initial conditions (more
precisely, to the linear growing mode). This allows us to write an explicit
path-integral expression for the probability distribution of the exact
non-linear density field.


title: Chemical evolution and abundance gradients in the Milky Way

abstract:
  We extend our model of chemical evolution that successfully account for the
main observables in the solar neighborhood (Alibes, Labay & Canal 2001) to the
whole Milky Way halo and disk. We assume an inside-out scenario for the
assembling of the Galaxy through the infall of external material. Two different
compositions of the infalling material have been considered: primordial and
slightly metal-enriched (0.1 Z_{\sun}). Our calculations follow the evolution
of 76 isotopes up to the Iron peak, but we only present here results for the
elements having well-measured gradients: C, N, O, Ne, Mg, Al, Si, S, Ar and Fe.
The calculated current radial distributions of these elements are compared with
large samples of data from HII regions, B stars, planetary nebulae and open
clusters. We also discuss the time evolution of the abundance gradients. Good
fits are achieved with both infall compositions, closer to the observational
data in the case of primordial infall. We show that contributions from
intermediate-mass stars allow to reproduce the measured abundances of C and N,
but the profiles of their ratios to oxygen leave still open the nucleosynthetic
origin of these elements. In agreement with several previous works, our models
predict a flattening with time of the abundance gradients, most of which taking
place during the early galactic evolution.


title:
Multiband optical polarimetry of BL Lac objects with the Nordic Optical
  Telescope

abstract:
  Optical polarization of seven selected BL Lac objects in UBVRI bands was
studied with the Nordic Optical Telescope from December 10-14, 1999. Two of
them, 3C 66A and PKS 0735+178, were monitored for 4 nights for a total
integration time of 4.75 and 5.5 hours, respectively. Other objects (1Jy
0138-097, H 0414+009, PKS 0823-223, OJ287 and BL Lac) were observed sparsely
during the run. Apart from PKS 0823-223 (more polarized than observed in the
past), the sources show levels of flux and polarization consistent with results
at previous epochs. 3C 66A and PKS 0735+178 were intensively observed during
December 11 and 12 and exhibited variability of polarization, both on
internight and intranight time scales. Wavelength dependence of polarization
has been investigated, as well as circular polarization. The results are
discussed within the standard model for BL Lacs.


title: The Galactic disk mass-budget : I. stellar mass-function and density

abstract:
  In this paper, we use the general theory worked out within the past few years
for the structure and the evolution of low-mass stars to derive the stellar
mass-function in the Galactic disk down to the vicinity of the hydrogen-burning
limit, from the observed nearby luminosity functions. The accuracy of the
mass-magnitude relationships derived from the afore-mentioned theory is
examined by comparison with recent, accurate observational relationships in the
M-dwarf domain. The mass function is shown to flatten out below $\sim 1 \msol$
but to keep rising down to the bottom of the main sequence. Combining the
present determination below 1 $\msol$ and Scalo's (1986) mass function for
larger masses, we show that the mass function is well described over the entire
stellar mass range, from $\sim 100 \msol$ to $\sim 0.1 \msol$, by three
functional forms, namely a two-segment power-law, a log-normal form or an
exponential form, all normalized to the Hipparcos sample at 0.8 $\msol$.
Integration of this mass function yields a reasonably accurate census of the
entire stellar population in the Galactic disk, and its volume and surface
mass-density.