title:
Carbon and Oxygen Galactic Abundance Gradients: A Comparative Study of
  Stellar Yields

abstract:
  Chemical evolution models for the Galactic disk under an inside-out formation
scenario are presented for seven sets of stellar yields, all of them metal
dependent. In particular, the effects of yields from massive and
low-and-intermediate-mass stars on the C/O chemical history of the solar
neighborhood and on abundance gradients are discussed comparing the predictions
with abundance ratios from nearby HII regions, B-stars, dwarf stars, and the
Sun.
  In the solar vicinity, the increase of C/O with metallicity is due to massive
stars alone. Models with yields by Maeder (1992) or by Portinari, Chiosi, &
Bressan (1998) reproduce the observed C/O increase with metallicity, while
models assuming yields by Woosley & Weaver (1995) and Woosley, Langer, & Weaver
(1993) do not. Models based on yields by Maeder (1992) are in agreement with
the C/O gradient, while those based on yields by Portinari et al. (1998) or by
Woosley & Weaver (1995) and Woosley et al. (1993) are not. To match both, the
C/O enrichment history of the solar neighborhood and the C/O local gradient,
models call for: i) yields that take into account metal-dependent stellar
winds; and ii) for massive stars, a mass-loss rate with a metallicity
dependence not as simple as Z^{0.5}.
  C/O abundance ratios predicted with yields by Marigo, Bressan, & Chiosi
(1996, 1998) are higher than those with yields by Renzini & Voli (1981), which
in turn are higher than those with yields by the van den Hoek & Groenewegen
(1997).


title: Gravitation Wave Emission from Radio Pulsars Revisited

abstract:
  We report a new pulsar population synthesis based on Monte Carlo techniques,
aiming to estimate the contribution of galactic radio pulsars to the continuous
gravitational wave emission. Assuming that the rotation periods of pulsars at
birth have a Gaussian distribution, we find that the average initial period is
290 ms. The number of objects with periods equal to or less than 0.4 s, and
therefore capable of being detected by an interferometric gravitational antenna
like VIRGO, is of the order of 5100-7800. With integration times lasting
between 2 and 3 yr, our simulations suggest that about two detections should be
possible, if the mean equatorial ellipticity of the pulsars is $\epsilon$
=10$^{-6}$. A mean ellipticity an order of magnitude higher increases the
expected number of detections to 12-18, whereas for $\epsilon < 10^{-6}$, no
detections are expected


title: Gravitational Waves from Mesoscopic Dynamics of the Extra Dimensions

abstract:
  Recent models which describe our world as a brane embedded in a higher
dimensional space introduce new geometrical degrees of freedom: the shape
and/or size of the extra dimensions, and the position of the brane. These modes
can be coherently excited by symmetry breaking in the early universe even on
``mesoscopic'' scales as large as 1 mm, leading to detectable gravitational
radiation. Two sources are described: relativistic turbulence caused by a
first-order transition of a radion potential, and Kibble excitation of
Nambu-Goldstone modes of brane displacement. Characteristic scales and spectral
properties are estimated and the prospects for observation by LISA are
discussed. Extra dimensions with scale between 10 \AA and 1 mm, which enter the
3+1-D era at cosmic temperatures between 1 and 1000 TeV, produce backgrounds
with energy peaked at observed frequencies in the LISA band, between $10^{-1}$
and $10^{-4}$ Hz. The background is detectable above instrument and
astrophysical foregrounds if initial metric perturbations are excited to a
fractional amplitude of $10^{-3}$ or more, a likely outcome for the
Nambu-Goldstone excitations.


title: FUSE Observations of O VI Absorption in the Galactic Halo

abstract:
  Far-ultraviolet spectra of 11 AGNs observed by FUSE are analyzed to obtain
measures of O VI 1031.93 A absorption occurring over very long paths through
Milky Way halo gas. Strong O VI absorption is detected along 10 of 11 sight
lines. Values of log [N(O VI) sin|b|] range from 13.80 to 14.64 with a median
value of 14.21. The observations reveal the existence of a widespread but
irregular distribution of O VI in the Milky Way halo. Combined with estimates
of the O VI mid-plane density, n0 = 2x10^(-8) cm^(-3), from the Copernicus
satellite, the FUSE observations imply an O VI exponential scale height of
2.7+/-0.4 kpc. We find that N(C IV)/N(O VI) ranges from 0.15 in the disk to 0.6
along four extragalactic sight lines. The changing ionization state of the gas
from the disk to the halo is consistent with a systematic decrease in the scale
heights of Si IV, C IV, N V, to O VI from ~5.1 to ~2.7 kpc. While conductive
heating models can account for the highly ionized atoms at low |z|, a
combination of models (and processes) appears to be required to explain the
highly ionized atoms found in the halo. The greater scale heights of Si IV and
C IV compared to O VI suggest that some of the Si IV and C IV in the halo is
produced in turbulent mixing layers or by photoionization by hot halo stars or
the extragalactic background.


title: A Search for OH Megamasers at z > 0.1. I. Preliminary Results

abstract:
  We present the preliminary results of a survey for OH megamasers underway at
the Arecibo Observatory. The goals of the survey are to calibrate the
luminosity function of OH megamasers to the low-redshift galaxy merger rate
(0.1 < z < 0.2), and to use the enhanced sample of OH megamasers provided by
the survey to study OH megamaser environments, engines, lifetimes, and
structure. The survey should double the known OH megamaser sample to roughly
100 objects. Survey results will be presented in installments to facilitate
community access to the data. Here we report the discovery of 11 OH megamasers
and one OH absorber, and include upper limits on the isotropic 1667 MHz OH line
luminosity of 53 other luminous infrared galaxies at z > 0.1. The new
megamasers show a wide range of spectral properties, but are consistent with
the extant set of 55 previously reported objects, only 8 of which have z > 0.1.


title: A Candidate Substellar Companion to HR 7329

abstract:
  We present the discovery of a candidate substellar companion from a survey of
nearby, young stars with the NICMOS coronagraph on the Hubble Space Telescope.
The H ~ 12 mag object was discovered approximately 4" from the young A0V star
HR 7329. Using follow-up spectroscopy from STIS, we derive a spectral type
between M7V and M8V with an effective temperature of ~ 2600 K. We estimate that
the probability of a chance alignment with a foreground dwarf star of this
nature is ~ 10^(-8) and therefore suggest the object (HR 7329B) is physically
associated with HR 7329 with a projected separation of 200 AU. Current brown
dwarf cooling models indicate a mass of less than 50 Jupiter masses for HR
7329B based on age estimates of < 30 Myr for HR7329A.


title: Timescales of disk evolution and planet formation

abstract:
  We present high-spatial resolution HST and adaptive optics observations, and
high-sensitivity ISO (ISOCAM & ISOPHOT) observations of a sample of X-ray
selected weak-line (WTTS) and post (PTTS) T Tauri stars located in the nearby
Chamaeleon T and Scorpius-Centaurus OB associations. HST/NICMOS and adaptive
optics observations aimed at identifying substellar companions at separations
>=30 A.U. from the primary stars. No such objects were found within 300 A.U. of
any of the target stars, and a number of faint objects at larger separations
can very likely be attributed to a population of background stars. ISOCAM
observations of 5 to 15 Myr old WTTS and PTTS in ScoCen reveal infrared
excesses which are clearly above photospheric levels, and which have a spectral
index intermediate between that of younger (1 to 5 Myr) T Tauri stars in Cha
and that of pure stellar photospheres. The difference in the spectral index of
the older PTTS in ScoCen compared to the younger classical and WTTS in Cha can
be attributed to a deficiency of smaller size (0.1 to 1mu) dust grains relative
to larger size (~5mu) dust grains in the disks of the PTTS. The lack of small
dust grains is either due to the environment (effect of nearby O stars and
supernova explosions) or due to disk evolution. If the latter is the case, it
would hint that circumstellar disks start to get dust depleted at an age
between 5 to 15 Myr. Dust depletion is very likely related to the build-up of
larger particles (ultimately rocks and planetesimals) and thus an indicator for
the onset of the period of planet formation.


title: On Estimating the QSO Transmission Power Spectrum

abstract:
  We present new methods to minimize the systematic and random errors for
measuring the transmission power spectrum from the Lyman-alpha forest. Sources
of systematic errors explored include metal line contamination and
continuum-fitting. We advocate the technique of trend-removal in place of
traditional continuum-fitting -- here, a spectrum is normalized by its
(smoothly varying) mean rather than its continuum -- this method is easily
automated and removes biases introduced by continuum-fitting. Trend- removal
can be easily applied to spectra where continuum-fitting is difficult, such as
when the resolution or signal-to-noise is low, or for spectra at high
redshifts. Furthermore, a measurement of the continuum power spectrum using
trend-removal, from either low redshift quasar spectra or the red-side of
Lyman-alpha, allows in principle the removal of spurious power introduced by
the continuum and thereby expanding scales probed to larger ones. We also
derive expressions for the shot-noise bias and variance of the power spectrum
estimate, taking into account the non-Poissonian nature of the shot-noise and
the non-Gaussianity of the cosmic fluctuations. An appropriate minimum variance
weighting of the data is given. Finally, we give practical suggestions on
observing strategy: the desired resolution and S/N for different purposes, and
how to distribute one's finite observing time among quasar targets. Also
discussed is the quasar spectroscopic study of the Sloan Digital Sky Survey,
which has the potential to measure the power spectrum at z ~ 2-4 accurate to
better than 1 % per mode -- the techniques presented here will be useful for
tackling the anticipated issues of shot-noise and continuum contamination.


title:
Nereid Has Complex Large-Amplitude Photometric Variability (Due to
  Chaotic Rotation)

abstract:
  We report on 224 photometric measurements of Nereid, a small outer satellite
of Neptune. Our photometry covers 64 nights from 1987 to 1997 and is primarily
in the V-band; we also have 20 measurements in the U, B, R, and I bands. (1)
Nereid displays large-amplitude brightness variations with a total amplitude of
1.83 mag on time scales ranging from a few hours to roughly a year. (2) The
amplitude as well as the time scale of variation changes greatly from year to
year. (3) Nereid's variability is caused by high contrast albedo features along
with rotational modulation. (4) The changing amplitudes and time scales
demonstrate that the direction and magnitude of Nereid's rotational angular
momentum vector is not constant. (5) Such changes are predicted to arise from
chaotic rotation during every periapse passage provided that Nereid is more
than about 1% nonspherical and is spinning slowly. The match between prediction
and observation could be taken as strong evidence for chaotic rotation of
Nereid. However, the intranight variability cannot be readily explained by
chaotic rotation. (6) The colors of Nereid are U-V=0.84+-0.05, B-V=0.71+-0.04,
V-R=0.44+-0.03, V-I=0.72+-0.05, and V-K=1.6. (7) Nereid is likely either an
inner moon of Neptune kicked to its current orbit or a captured Kuiper Belt
Object or centaur, with the latter possibility being strongly preferred.


title:
Sgr A* Polarization: No ADAF, Low Accretion Rate, and Non-Thermal
  Synchrotron Emission

abstract:
  The recent detection of polarized radiation from Sgr A* requires a
non-thermal electron distribution for the emitting plasma. The Faraday rotation
measure must be small, placing strong limits on the density and magnetic field
strength. We show that these constraints rule out advection-dominated accretion
flow models. We construct a simple two-component model which can reproduce both
the radio to mm spectrum and the polarization. This model predicts that the
polarization should rise to nearly 100% at shorter wavelengths. The first
component, possibly a black-hole powered jet, is compact, low density, and
self-absorbed near 1 mm with ordered magnetic field, relativistic Alfven speed,
and a non-thermal electron distribution. The second component is poorly
constrained, but may be a convection-dominated accretion flow with dM/dt~10^-9
M_Sun/yr, in which feedback from accretion onto the black hole suppresses the
accretion rate at large radii. The black hole shadow should be detectable with
sub-mm VLBI.


title:
Hubble Space Telescope Imaging of Bipolar Nuclear Shells in the
  Disturbed Virgo Cluster Galaxy NGC 4438

abstract:
  We present broadband and narrowband Hubble Space Telescope images of the
central region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp120),
whose nucleus has been described as a type 1 LINER or dwarf Seyfert. Narrowband
H-alpha and [NII] HST images reveal striking bipolar shell features, 1 kpc in
projected length from end-to-end, which are likely the result of an outflow
from the nuclear region experiencing a strong interaction with the ISM. While
these outflow shells share similarities with those in some other starburst or
AGN galaxies, these in NGC 4438 are notable because NGC 4438 harbors neither a
luminous circumnuclear starburst nor a luminous AGN. The shells appear to be
closed at their outer ends, suggesting that the outflow in NGC 4438 is
dynamically younger than those in some other galaxies. The radio continuum
emission is strongly enhanced near the outer ends of the shells, suggesting
working surfaces arising from collimated nuclear outflows which have impacted
and shocked the surrounding ISM. The 2 shells are quite different, as the
northwestern (NW) shell is luminous and compact, while the southeastern (SE)
shell is 2.5 times longer and much fainter, in both optical emission lines and
the non-thermal radio continuum. The differences between the 2 shells may be
attributed to a difference in ISM density on the 2 sides of the nuclear disk.
Such an ISM asymmetry exists on larger scales in this heavily disturbed galaxy.
At the base of the outflow is a nuclear source, which is the highest surface
brightness source in the galaxy at optical wavelengths, We discuss whether the
outflow is powered by a low luminosity AGN or a compact nuclear starburst.


title: The Merging System Am 2049-691

abstract:
  Spectroscopic and photometric observations of the peculiar object AM 2049-691
are presented here. Its systemic velocity is V(GSR) = (10956 +-30) km/s, and
the derived distance (H(0) = 75 km/s/Mpc) results 146 Mpc. A bridge is observed
between two very distinct nuclei whose separation is about 10 kpc, as well as
two tails that emerge from the extremes SW and NE of the main body and extend
up to 41 and 58 kpc respectively. The spectral characteristics of the all
observed zones are typical of H II regions of low excitation. The internal
reddening is quit high, particularly in the NE nucleus. All the derived
equivalent widths of the H(alpha)+[N II] lines indicate enhanced star formation
compared with isolated galaxies, specially in the NE nucleus; the equivalent
width corresponding to the integrated spectrum reflects starburst activity in
the whole object, and is compatible with a merger of two disk galaxies. All the
observed characteristics of AM 2049-691 indicate it is a merger, where a
overabundance of nitrogen is detected in one of the nuclei, which has the most
evolved population and would be the most massive one. The detected total IR
emission is not very high. The integrated total color B - V corresponds to a
Sc-Scd galaxy and its average integrated population is about F7 type.
Indicative B - V colors of the nuclei, corrected for internal absorption, are
in agreement with the spectroscopic results. The central radial velocity
dispersions at the nuclei suggest that the most massive galaxy would be the
progenitor of the SW component. The observed radial velocity curve shows the
presence of two subsystems, each one associated with a different nucleus.


title: Bar Dissolution in Prolate Halos

abstract:
  The time evolution of barred structures is examined under the influence of
the external forces exerted by a spherical halo and by prolate halos. In
particular, galaxy disks are placed in the plane including the major axis of
prolate halos, whose configuration is often found in cosmological simulations.
N-body disks in fixed external halo fields are simulated, so that bars are
formed via dynamical instability. In the subsequent evolution, the bars in
prolate halos dissolve gradually with time, while the bar pattern in a
spherical halo remains almost unchanged to the end of the simulation. The decay
times of the bars suggest that they can be destroyed in a time smaller than a
Hubble time. Our results indicate that this dissolution process could occur in
real barred galaxies, if they are surrounded by massive dark prolate halos, and
the configuration adopted here is not unusual from the viewpoint of galaxy
formation. For a prolate halo model, an additional simulation that is
restricted to two-dimensional in-plane motions has also ended up with similar
bar dissolution. This means that the vertical motions of disk stars do not play
an essential role in the bar dissolution demonstrated here.


title: Production of Lithium in the Galactic Disk

abstract:
  We examine the evolution of Li in the Galactic disk,basing our model on the
compilation of Li v.Fe observations in stars of iron abundance ranging between
halo values,which give a baseline for the disk Li abundance,and 0.2 dex above
solar.The upper envelope of these observations is taken to represent the locus
of minimum stellar Li depletion,and thus to follow the Galactic IS Li
abundance.The most striking feature of this envelope is its steep rise between
Fe/H ~ -0.4 and -0.2,corresponding to a relatively late epoch.The Li abundance
increases by an order of magnitude,from its halo value of logLi ~2.2 to the
"current" value of ~3.2 within this narrow range of Fe abundances.It is well
known that spallation reactions between CNO and 4He in the ISM produce Li,but
models give a nearly tenfold shortfall for this process.The alpha+alpha fusion
reaction appeared to yield too much early Li or too little current Li.These
failures led to the exploration of stellar sources:supernovae,novae,and the He
flash phase in AGB stars.The Li-Fe envelope is a strong constraint on any
process.Our models can account for this in the context of disk chemical
evolution with a near constant or growing rate of low metallicity gas
infall,and a purely interstellar Li source: alpha-alpha fusion.The Li
production rate is found to be proportional to the gas expulsion rate from
intermediate and low mass stars.Low-energy alphas,emitted by these stars,but
accelerated in more energetic processes associated with SNe,or the bow-shocks
of stellar winds,can yield the observed abundance and its variation with Fe or
O.Our model is consistent with the cosmic ray spectrum in the few MeV
range,corrected for solar modulation and with new 7Li/6Li ratios found by
Knauth et al.(2000) in the local ISM.


title: Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)

abstract:
  We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand
2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet
at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo
2.3m optical spectroscopy, and analysed using a spherical, non-LTE,
line-blanketed code. Our study reveals exceptional stellar parameters:
T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt
a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and
O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination
line studies. We confirm that Sand 2 is more chemically enriched in carbon than
LMC WC stars, and is expected to undergo a supernova explosion within the next
50,000 yr.


title:
The morphology of the Magellanic Clouds revealed by stars of different
  age: results from the DENIS survey

abstract:
  The spatial distribution of sources populating different regions of the
colour-magnitude diagram (I-J, I) extracted from the DENIS catalogue towards
the Magellanic Clouds (DCMC -- Cioni et al. 2000) reveal significantly
different morphologies. Each region is associated to a different age group. The
Large Magellanic Cloud (LMC) shows an extended circular shape with a prominent,
off center bar, a nucleus and irregular spiral arms. The Small Magellanic Cloud
shows a perturbated structure with a prominent central concentration of stars.
Old and young populations are offset from one another.


title:
Search for clusters at high redshift - I. Candidate Lya emitters near
  1138-262 at z=2.2

abstract:
  Radio, optical and X-ray observations of the powerful radio galaxy PKS
1138-262 at z=2.156 have suggested that this galaxy is a massive galaxy in the
center of a forming cluster. We have imaged 1138-262 and the surrounding 38
square arcminute field with the Very Large Telescope in a broad band and a
narrow band encompassing the redshifted Lya emission. We detect 50 objects with
rest equivalent width larger than 20 A and a luminous, highly extended Lya halo
around 1138-262. If the radio galaxy is at the center of a forming cluster,
these objects are candidate Lya emitting cluster galaxies.


title:
Prospects for SIMPLE 2000: A large-mass, low-background Superheated
  Droplet Detector for WIMP searches

abstract:
  SIMPLE 2000 (Superheated Instrument for Massive ParticLE searches) will
consist of an array of eight to sixteen large active mass ($\sim15$ g)
Superheated Droplet Detectors(SDDs) to be installed in the new underground
laboratory of Rustrel-Pays d'Apt. Several factors make of SDDs an attractive
approach for the detection of Weakly Interacting Massive Particles (WIMPs),
namely their intrinsic insensitivity to minimum ionizing particles, high
fluorine content, low cost and operation near ambient pressure and temperature.
We comment here on the fabrication, calibration and already-competitive first
limits from SIMPLE prototype SDDs, as well as on the expected immediate
increase in sensitivity of the program, which aims at an exposure of $>$25
kg-day during the year 2000. The ability of modest-mass fluorine-rich detectors
to explore regions of neutralino parameter space beyond the reach of the most
ambitious cryogenic projects is pointed out.

categories: astro-ph cond-mat.soft hep-ex hep-ph nucl-ex physics.ins-det


title: ISO Observations of Pre-Main Sequence and Vega-type Stars

abstract:
  I present an overview of the results obtained by the Infrared Space
Observatory (ISO) on circumstellar material in pre-main sequence (PMS) stars.
Results obtained for embedded YSOs, Herbig Ae/Be systems and T Tauri stars are
reviewed and their connection to the disks around Vega-type systems is
discussed. Although the gas contents of the PMS environment will also be
discussed briefly, this review will mainly focus on the composition, mineralogy
and evolution of dust in these systems, and the results will be compared to
those found in other classes of objects, including solar system comets.


title: A bright X-ray transient towards NGC 5128 (Centaurus A)

abstract:
  During five ROSAT HRI observations in July 1995, a bright X-ray source
(designated 1RXH J132519.8-430312) was detected 2.5' south-west of the nucleus
of NGC 5128 (Centaurus A) at the outer regions of the elliptical galaxy. At
that time it was the brightest point source in the ROSAT HRI field-of-view. All
other ROSAT observations made before and after these observations show no trace
of the source suggesting that this is a highly variable object. Chandra
observations of Cen A made in September 1999 show a source at the ROSAT
position which may be the quiescent counterpart of the transient. It is very
probable that the transient is located in NGC 5128. Given the existence of a
transient source that close to the direction of NGC 5128, all observations (at
least in soft X-rays) of Cen A, with instruments of low spatial resolution,
must take the presence and variability of this object into account.


title: EUV Flare Activity in Late-Type Stars

abstract:
  \textit{Extreme Ultraviolet Explorer} Deep Survey observations of cool stars
(spectral type F to M) have been used to investigate the distribution of
coronal flare rates in energy and its relation to activity indicators and
rotation parameters. Cumulative and differential flare rate distributions were
constructed and fitted with different methods. Power laws are found to
approximately describe the distributions. A trend toward flatter distributions
for later-type stars is suggested in our sample. Assuming that the power laws
continue below the detection limit, we have estimated that the superposition of
flares with radiated energies of about $10^{29}-10^{31}$ergs could explain the
observed radiative power loss of these coronae, while the detected flares are
contributing only $\approx 10$%. While the power-law index is not correlated
with rotation parameters (rotation period, projected rotational velocity,
Rossby number) and only marginally with the X-ray luminosity, the flare
occurrence rate is correlated with all of them. The occurrence rate of flares
with energies larger than $10^{32}$ergs is found to be proportional to the
average total stellar X-ray luminosity. Thus, energetic flares occur more often
in X-ray bright stars than in X-ray faint stars. The normalized occurrence rate
of flares with energies larger than $10^{32}$ergs increases with increasing
\lxlbol and stays constant for saturated stars. A similar saturation is found
below a critical Rossby number. The findings are discussed in terms of simple
statistical flare models in an attempt to explain the previously observed trend
for higher average coronal temperatures in more active stars. It is concluded
that flares can contribute a significant amount of energy to coronal heating in
active stars.


title: Voids in the LCRS versus CDM Models

abstract:
  We have analyzed the distribution of void sizes in the two-dimensional slices
of the Las Campanas Redshift Survey (LCRS). Fourteen volume-limited subsamples
were extracted from the six slices to cover a large part of the survey and to
test the robustness of the results against cosmic variance. Thirteen samples
were randomly culled to produce homogeneously selected samples. We then studied
the relationship between the cumulative area covered by voids and the void size
as a property of the void hierarchy. We find that the distribution of void
sizes scales with the mean galaxy separation, $\lambda$. In particular, we find
that the size of voids covering half of the area is given by $D_{med} \approx
\lambda + (12\pm3) \h^{-2}$Mpc. Next, by employing an environmental density
threshold criterion to identify mock galaxies, we were able to extend this
analysis to mock samples from dynamical $n$-body simulations of Cold Dark
Matter (CDM) models. To reproduce the observed void statistics, overdensity
thresholds of $\delta_{th} \approx 0 ... 1$ are necessary. We have compared
standard (SCDM), open (OCDM), vacuum energy dominated ($\Lambda$CDM), and
broken scale invariant CDM models (BCDM): we find that both the void coverage
distribution and the two-point correlation function provide important and
complementary information on the large-scale matter distribution. The
dependence of the void statistics on the threshold criterion for the mock
galaxy indentification shows that the galaxy biasing is more crucial for the
void size distribution than are differences between the cosmological models.


title: What hides at the center of the Sun ?

abstract:
  The Standard Solar Model (SSM) and its basic assumption of an equation of
state of perfect gases for the plasmas of its interior is analyzed within the
new theoretical framework of QED coherent states. We find that for
$\frac{r}{r_{\odot}}\leq 0.3$ the SSM solution is unstable against collapse to
a dense, {\it cold} coherent core and as a result a large suppression of
$B^{8}$-neutrinos is obtained, apparently solving the long standing solar
neutrino problem.


title: A spectroscopic study of NGC 6251 and its companion galaxies

abstract:
  Measurements of the velocities of galaxies thought to be associated with the
giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a
systemic redshift of z= 0.0244 +/- 0.0004 and a line-of-sight velocity
dispersion of sigma_{z}= 283 (+109, -52) km/s. This suggests a cluster
atmosphere temperature of T = 0.7 (+0.6, -0.2) keV, which is not enough to
confine the radio jet by gas pressure. The core of NGC 6251 shows strong
emission lines of [O III] and H alpha + [N II], but there is no evidence for
line emission from the jet (detected in optical continuum by Keel (1988)).


title:
X-ray Emission of Mkn 421: New Clues From Its Spectral Evolution. I.
  Temporal Analysis

abstract:
  Mkn 421 was repeatedly observed with BeppoSAX in 1997-1998. This is the first
of two papers where we present the results of a thorough temporal and spectral
analysis of all the data available to us, focusing in particular on the flare
of April 1998, which was simultaneously observed also at TeV energies. Here we
focus on the time analysis, while the spectral analysis and physical
interpretation are presented in the companion paper. The detailed study of the
flare in different energy bands reveals very important new results: i) hard
photons lag the soft ones by 2-3 ks -a behavior opposite to what is normally
found in high energy peak BL Lacs X-ray spectra; ii) the flare light curve is
symmetric in the softest X-ray band, while it becomes increasingly asymmetric
at higher energies, with the decay being progressively slower than the rise;
iii) the flux decay of the flare can be intrinsically achromatic if a
stationary underlying emission component is present. The temporal and spectral
information obtained challenge the simplest models currently adopted for the
(synchrotron) emission and most importantly provide clues on the particle
acceleration process.


title:
X-ray Emission of Mkn 421: New Clues From Its Spectral Evolution. II.
  Spectral Analysis and Physical Constraints

abstract:
  Mkn 421 was repeatedly observed with BeppoSAX in 1997-1998. The source showed
a very rich phenomenology, with remarkable spectral variability. This is the
second of two papers presenting the results of a thorough temporal and spectral
analysis of all the data available to us, focusing in particular on the flare
of April 1998, which was simultaneously observed also at TeV energies. The
spectral analysis and correlations are presented in this paper, while the data
reduction and timing analysis are the content of the companion paper. The
spectral evolution during the flare has been followed over few ks intervals,
allowing us to detect for the first time the peak of the synchrotron component
shifting to higher energies during the rising phase, and then receding. This
spectral analysis nicely confirms the delay of the flare at the higher
energies, which in Paper I we quantified as a hard lag of a few ks.
Furthermore, at the highest energies, evidence is found of variations of the
inverse Compton component. The spectral and temporal information obtained
challenge the simplest models currently adopted for the (synchrotron) emission
and most importantly provide clues on the particle acceleration process. A
scenario accounting for all the observational constraints is discussed, where
electrons are injected at progressively higher energies during the development
of the flare, and the achromatic decay is ascribed to the source light crossing
time exceeding the particle cooling timescales.


title:
Wide Field Imaging of the Hubble Deep Field-South Region I: Quasar
  Candidates

abstract:
  We present candidate quasars from a multi-color (uBVRI + narrow-band) imaging
survey of 1/2 square degree around the Hubble Deep Field - South. We identify
154 candidate quasars with B < 23 using color selection, consistent with
previously measured QSO number counts if we assume a 60% selection efficiency.
The narrow-band filter (NB) was centered at 3958 A to detect Ly-alpha at the
redshift of J2233-6033, the HDF-S QSO. We confirm the presence of Ly-alpha
nebulosity extending ~12'' around the HDF-S QSO, reported by Bergeron et al.
(1999). We detect 10 point-like objects in emission through the NB filter. Of
these, 7 satisfy our QSO color selection criteria. One of emission-line objects
is a B~20 radio-quiet quasar at z=1.56, 6.7' from the line of sight to the
HDF-S QSO and ~12'' from the western edge of the WFPC2 deep field.


title: The Global Cosmological Parameters

abstract:
  This lecture note presents a survey of the current status of the
determination of the three cosmological parameters, the Hubble constant, the
mass density paramater and the cosmological constant, to the closing date of
the end of November 1999.


title: Enlarged quintessence cosmology

abstract:
  We show that the combination of a fluid with a bulk dissipative pressure and
quintessence matter can simultaneously drive an accelerated expansion phase and
solve the coincidence problem of our current Universe. We then study some
scenarios compatible with the observed cosmic acceleration.


title:
An Interpretation of the Evidence for TeV Emission from Gamma-Ray Burst
  970417a

abstract:
  The Milagrito collaboration recently reported evidence for emission of very
high energy gamma-rays in the TeV range from one of the BATSE GRBs, GRB
970417a. Here I discuss possible interpretations of this result. Taking into
account the intergalactic absorption of TeV gamma-rays by the cosmic infrared
background, I found that the detection rate (one per 54 GRBs observed by the
Milagrito) and energy fluence can be consistently explained with the redshift
of this GRB at z \sim 0.7 and the isotropic total energy in the TeV range,
E_{TeV, iso} >~ 10^{54} erg. This energy scale is not unreasonably large, but
interestingly similar to the maximum total GRB energy observed to date, in the
sub-MeV range for GRB 990123. On the other hand, the energy emitted in the
ordinary sub-MeV range becomes E_{MeV, iso} \sim 10^{51} erg for the GRB
970417a, which is much smaller than the total energy in the TeV range by a
factor of about 10^3. I show that the proton-synchrotron model of GRBs provides
a possible explanation for these observational results. I also discuss some
observational signatures expected in the future experiments from this model.


title:
Compton Scattering in Ultra-Strong Magnetic Fields: Numerical and
  Analytical Behavior in the Relativistic Regime

abstract:
  This paper explores the effects of strong magnetic fields on the Compton
scattering of relativistic electrons. Recent studies of upscattering and energy
loss by relativistic electrons that have used the non-relativistic, magnetic
Thomson cross section for resonant scattering or the Klein-Nishina cross
section for non-resonant scattering do not account for the relativistic quantum
effects of strong fields ($ > 4 \times 10^{12}$ G). We have derived a
simplified expression for the exact QED scattering cross section for the
broadly-applicable case where relativistic electrons move along the magnetic
field. To facilitate applications to astrophysical models, we have also
developed compact approximate expressions for both the differential and total
polarization-dependent cross sections, with the latter representing well the
exact total QED cross section even at the high fields believed to be present in
environments near the stellar surfaces of Soft Gamma-Ray Repeaters and
Anomalous X-Ray Pulsars. We find that strong magnetic fields significantly
lower the Compton scattering cross section below and at the resonance, when the
incident photon energy exceeds $m_ec^2$ in the electron rest frame. The cross
section is strongly dependent on the polarization of the final scattered
photon. Below the cyclotron fundamental, mostly photons of perpendicular
polarization are produced in scatterings, a situation that also arises above
this resonance for sub-critical fields. However, an interesting discovery is
that for super-critical fields, a preponderance of photons of parallel
polarization results from scatterings above the cyclotron fundamental. This
characteristic is both a relativistic and magnetic effect not present in the
Thomson or Klein-Nishina limits.


title: X-rays from Quiescent Low-Mass X-ray Binary Transients

abstract:
  I argue that it is very unlikely that X-rays from quiescent black-hole
low-mass X-ray binary transients are emitted by coronae of companion stars. I
show that in a simple model in which these X-rays are emitted by an ADAF
filling the inner part of an unsteady, dwarf-nova type disc, the X-ray
luminosity is correlated with the orbital period. I predict what values of
X-ray luminosities from black-hole transient systems should be observed by
Chandra and XMM-Newton.


title: High order symplectic integrators for perturbed Hamiltonian systems

abstract:
  We present a class of symplectic integrators adapted for the integration of
perturbed Hamiltonian systems of the form $H=A+\epsilon B$. We give a
constructive proof that for all integer $p$, there exists an integrator with
positive steps with a remainder of order $O(\tau^p\epsilon +\tau^2\epsilon^2)$,
where $\tau$ is the stepsize of the integrator. The analytical expressions of
the leading terms of the remainders are given at all orders. In many cases, a
corrector step can be performed such that the remainder becomes
$O(\tau^p\epsilon +\tau^4\epsilon^2)$. The performances of these integrators
are compared for the simple pendulum and the planetary 3-Body problem of
Sun-Jupiter-Saturn.


title:
Cosmic ray acceleration at relativistic and ultrarelativistic shock
  waves

abstract:
  Using the Monte Carlo simulations we apply a method of discrete small
amplitude particle momentum scattering to reproduce highly anisotropic
conditions at relativistic shocks. We discusse acceleration times scales in
relativistic shocks. Next, we describe newly found acceleration mechanism at
ultrarelativistic shocks. The universal spectral index and the acceleration
time for the shocks are given. In the end reflections from ultrarelativistic
shocks are considered.


title: ISO observations of a sample of 60 micron peaker galaxies

abstract:
  The sample of IRAS galaxies with spectral energy distributions that peak near
60 microns are called Sixty Micron Peakers (SMPs or 60PKs). Their generally
peculiar and amorphous morphologies, hot dust and lack of a cirrus component
have been interpreted as being indicative of a recent interaction/merger event.
Mid-infrared spectra of eight SMPs, obtained with ISOPHOT-S in the ~2-11 micron
band are presented. Four of the observed sources are H II region-like (H2)
galaxies, three are Seyfert 2 and one is unclassified. Emission attributed to
Polycyclic Aromatic Hydrocarbons (PAHs) at 6.2, 7.7 and 8.6 micron is
ubiquitous in the spectra. The PHOT-S spectrum of the H2 galaxy IRAS 23446+1519
exhibits a bright 11.04 micron line and an 8.6 micron feature of comparable
size to its 7.7 micron feature. [S IV] emission at 10.5 micron was detected in
three of four H2 galaxies and in one Seyfert 2 galaxy. The ratio of the 7.7
\textmu m PAH feature to the continuum at 7.7 micron (PAH L/C) divides the
eight SMPs at a ratio greater than 0.8 for H2 and less than 0.8 for Seyfert
galaxies. An anti-correlation between PAH L/C and the ratio of the continuum
flux at 5.9 micron to the flux at 60 micron is found, similar to that found in
ultraluminous infrared galaxies. Silicate absorption at approximately 9.7
micron was observed in the Seyfert 2 galaxy, IRAS 04385-0828 and in IRAS
03344-2103. The previously unclassified SMP galaxy IRAS 03344-2103 is probably
a Seyfert 2.


title: A theoretical light-curve model for the 1985 outburst of RS Ophiuchi

abstract:
  A theoretical light-curve model of the 1985 outburst of RS Ophiuchi is
presented based on a thermonuclear runaway (TNR) model. The system consists of
a very massive white dwarf (WD) with an accretion disk (ACDK) and a red giant
(RG). The early phase of the V light curve is well reproduced only by the
bloated WD photosphere of the TNR model on a 1.35 +/- 0.01 M_sun WD while the
later phase is dominated both by the irradiated ACDK and by the irradiated RG
underfilling the inner critical Roche lobe. The UV light curve is also well
reproduced by the same model with the distance of 0.6 kpc to RS Oph. The
envelope mass at the optical peak is estimated to be 2 x 10^{-6} M_sun,
indicating a rather high mass accretion rate of 1.2 x 10^{-7} M_sun yr^{-1}
between the 1967 and the 1985 outbursts. About 90% of the envelope mass is
blown off in the outburst wind while the residual 10% (2 x 10^{-7} M_sun) has
been left and added to the helium layer of the WD. The net increasing rate of
the WD mass is 1.2 x 10^{-8} M_sun yr^{-1}. Thus, RS Oph is certainly a strong
candidate for a Type Ia supernova progenitor.


title: Oscillating structure of \gamma-bursts and their possible origin

abstract:
  As it is well-known that the hydrodinamic collapse of the massive star iron
core should lead to the production of a hot neutron star. The assumption is
made that the thermonuclear burning of the envelope matter, accreting onto the
hot neutron star, can proceed in the oscillatoric regime (analogously to that
happens during heat explosion of the carbon-oxigene cores of stars with smaller
masses). Local density oscillations in the vicinity of the neutron star surface
can generate shock waves, in which the stratification of the electron-positron
plasma from the rest of the matter can happen due to the light preasure. In the
case of the spherically symmetric collapse of the compact star it can lead to
the production of the expanding relativistic fireball shells with
characteristic oscillation time of ~ 10^{-2} s, observed in the cosmological
\gamma-bursts (GRB), can occur. It is pointed out that nonrotating massive
Wolf-Rayet's (WR) stars could be the source for the GRB, whose collapses,
according to a number of observations, can happen without any noticeable
ejection of the envelope.


title:
Dynamical processes, element mixing and chemodynamical cycles in dwarf
  galaxies

abstract:
  Since the chemical evolution of galaxies seems to differ between
morphological types and deviates in many details from the standard scenario the
question has to be addressed when, how and to what amount metal-enriched ejecta
from Supernovae and Planetary Nebulae polute their environment. Since recent
observations of dwarf galaxies show no significant metal abundance gradients
throughout the galaxies while enhancement of metals happens in isolated HII
regions, an effective mixing process has to be assumed. Chemodynamical
evolution models can provide a possible explanation by demonstrating that
strong evaporation of gas clouds by hot gas and following condensation leads to
an almost perfect mixing of the gas. We focus on the different phases of
chemodynamical evolution that are experienced by a representative dwarf
irregular galaxy model and present a quantitative analysis of the
chemodynamical gas flow cycles.


title:
Is the diffuse gamma background radiation generated by galactic cosmic
  rays?

abstract:
  We explore the possibility that the diffuse gamma-ray background radiation
(GBR) at high galactic latitudes could be dominated by inverse Compton
scattering of cosmic ray (CR) electrons on the cosmic microwave background
radiation and on starlight from our own galaxy. Assuming that the mechanisms
accelerating galactic CR hadrons and electrons are the same, we derive simple
and successful relations between the spectral indices of the GBR above a few
MeV, and of the CR electrons and CR nuclei above a few GeV. We reproduce the
observed intensity and angular dependence of the GBR, in directions away from
the galactic disk and centre, without recourse to hypothetical extragalactic
sources.


title:
Application of the Limit Cycle Model to Star Formation Histories in
  Spiral Galaxies: Variation among Morphological Types

abstract:
  We propose a limit-cycle scenario of star formation history for any
morphological type of spiral galaxies. It is known observationally that the
early-type spiral sample has a wider range of the present star formation rate
(SFR) than the late-type sample. This tendency is understood in the framework
of the limit-cycle model of the interstellar medium (ISM), in which the SFR
cyclically changes in accordance with the temporal variation of the mass
fraction of the three ISM components. When the limit-cycle model of the ISM is
applied, the amplitude of variation of the SFR is expected to change with the
supernova (SN) rate. Observational evidence indicates that the early-type
spiral galaxies show smaller rates of present SN than late-type ones. Combining
this evidence with the limit-cycle model of the ISM, we predict that the
early-type spiral galaxies show larger amplitudes in their SFR variation than
the late-types. Indeed, this prediction is consistent with the observed wider
range of the SFR in the early-type sample than in the late-type sample. Thus,
in the framework of the limit-cycle model of the ISM, we are able to interpret
the difference in the amplitude of SFR variation among the morphological
classes of spiral galaxies.


title:
An X-ray burst with strong photospheric radius expansion observed from
  the source 4U1724-307 in Terzan 2

abstract:
  We present results of the RXTE observations of an extremely intense X-ray
burst detected from the source 4U1724-307 in the globular cluster Terzan 2. The
burst profile was complex consisting of two precursors and a long primary peak.
During the first (strong) precursor the source luminosity, L ~ 3.6 x 10^38
erg/s, was comparable with that measured in the main event. The structure of
the profile, its dependence on energy and observed spectral evolution indicated
strong photospheric expansion of a neutron star. The effective temperature and
radius of the photosphere were estimated from the black body model at different
stages of expansion, their correlations and specific features of the profile
were analyzed and discussed.


title:
Mid-Infrared Observations of Normal Star-Forming Galaxies: The Infrared
  Space Observatory Key Project Sample

abstract:
  We present mid-infrared maps and preliminary analysis for 61 galaxies
observed with the ISOCAM instrument aboard the Infrared Space Observatory. Many
of the general features of galaxies observed at optical wavelengths---spiral
arms, disks, rings, and bright knots of emission---are also seen in the
mid-infrared, except the prominent optical bulges are absent at 6.75 and 15
microns. In addition, the maps are quite similar at 6.75 and 15 microns, except
for a few cases where a central starburst leads to lower 6.75/15 ratios in the
inner region. We also present infrared flux densities and mid-infrared sizes
for these galaxies. The mid-infrared color 6.75/15 shows a distinct trend with
the far-infrared color 60/100. The quiescent galaxies in our sample (60/100 <
0.6) show 6.75/15 near unity, whereas this ratio drops significantly for
galaxies with higher global heating intensity levels. Azimuthally-averaged
surface brightness profiles indicate the extent to which the mid-infrared flux
is centrally concentrated, and provide information on the radial dependence of
mid-infrared colors. The galaxies are mostly well resolved in these maps:
almost half of them have < 10% of their flux in the central resolution element.
A comparison of optical and mid-infrared isophotal profiles indicates that the
optical flux at 4400 Angstroms near the optical outskirts of the galaxies is
approximately eight (seven) times that at 6.75 microns (15 microns), comparable
with observations of the diffuse quiescent regions of the Milky Way.


title: Possible manifestations of the graviton background

abstract:
  Possible effects are considered which would be caused by a hypothetical
superstrong interaction of photons or massive bodies with single gravitons of
the graviton background. If full cosmological redshift magnitudes are caused by
the interaction, then the luminosity distance in a flat non-expanding universe
as a function of redshift is very similar to the specific function which fits
supernova cosmology data by Riess et al. From another side, in this case every
massive body, slowly moving relatively to the background, would experience a
constant acceleration, proportional to the Hubble constant, of the same order
as a small additional acceleration of Pioneer 10, 11.


title: The redshift space power spectrum in the halo model

abstract:
  Recently there has been a lot of attention focussed on a virialized
halo-based approach to understanding the properties of the matter and galaxy
power spectrum. We show that this model allows a natural treatment of the large
and small scale redshift space distortions, which we develop here, which
extends the pedagogical value of the approach.


title: Dynamics of the Galactic Bulge using Planetary Nebulae

abstract:
  Evidence for a bar at the center of the Milky Way triggered a renewed
enthusiasm for dynamical modelling of the Galactic bar-bulge. Our goal is to
compare the kinematics of a sample of tracers, planetary nebulae, widely
distributed over the bulge with the corresponding kinematics for a range of
models of the inner Galaxy. Three of these models are N-body barred systems
arising from the instabilities of a stellar disk (Sellwood, Fux and Kalnajs),
and one is a Schwarzschild system constructed to represent the 3D distribution
of the COBE/DIRBE near-IR light and then evolved as an N-body system for a few
dynamical times (Zhao). For the comparison of our data with the models, we use
a new technique developed by Saha (1998). The procedure finds the parameters of
each model, i.e. the solar galactocentric distance R_o in model units, the
orientation angle phi, the velocity scale (in km/s per model unit), and the
solar tangential velocity which best fit the data.


title: Skewness as a probe of non-Gaussian initial conditions

abstract:
  We compute the skewness of the matter distribution arising from non-linear
evolution and from non-Gaussian initial perturbations. We apply our result to a
very generic class of models with non-Gaussian initial conditions and we
estimate analytically the ratio between the skewness due to non-linear
clustering and the part due to the intrinsic non-Gaussianity of the models. We
finally extend our estimates to higher moments.


title:
Redshifts of 10 quasar candidates in the field of the rich absorption
  line quasar QSO 0122-380

abstract:
  We have obtained low resolution (~20 Angstrom FWHM) slit spectra of 10 quasar
candidates located within one degree of the z = 2.181 quasar Q0122-380 with the
objective of searching for signs of large scale structure matching the
intervening rich absorption complexes seen over the redshift range 1.81<z<1.97
toward this object. Of the 8 confirmed quasars, 4 turn out to have redshifts z
< 1.8, placing them well in front of the redshift range of interest. Two of the
three confirmed quasars at redshift z > 1.8 show no obvious absorption matching
that of Q0122-380 at our spectral resolution and signal-to-noise ratio. The
third object at a redshift of z = 1.868 displays strong z_{abs} \sim z_{em}
absorption systems at z = 1.84 and z = 1.86 and a possibly BAL-like trough at z
= 1.76. If not intrinsic in nature, the former two systems could potentially be
related to the absorption seen in Q0122-380, albeit over a distance of 50.2
arcmin (D_\perp \simeq 15 h^{-1} Mpc at z = 1.9).


title: Composition of UHE Cosmic Ray Primaries

abstract:
  Project GRAND presents results on the atomic composition of primary cosmic
rays. This is accomplished by determining the average height of primary
particles that cause extensive air showers detected by Project GRAND. Particles
with a larger cross sectional area, such as iron nuclei, are likely to start an
extensive air shower higher in the atmosphere whereas protons, with a smaller
cross section, would pass through more air before interacting and thus start
showers at lower heights. Such heights can be determined by extrapolating
identified muon tracks backward (upward) to determine their height of origin
(Gress et al., 1997). Since muons are from the top, hadronic part of the
shower, they are a good estimator for the beginning of the shower. The data for
this study were taken during the previous year with 20 million shower events.


title:
FUSE Observations of Molecular Hydrogen in Translucent Interstellar
  Clouds: The Line of Sight Toward HD 73882

abstract:
  We report the results of initial FUSE observations of molecular hydrogen (H2)
in translucent clouds. These clouds have greater optical depth than any of the
diffuse clouds previously observed for far-UV H2 absorption, and provide new
insights into the physics and chemistry of such regions. Our initial results
involve observations of HD 73882, a well-studied southern hemisphere star lying
behind substantial interstellar material (E(B-V) = 0.72; A_V = 2.44). We find a
total H2 column density, N(H2) = 1.2 x 10^{21} cm^{-2}, about three times
larger than the values for diffuse clouds previously measured in the far-UV.
The gas kinetic temperature indicated by the ratio N(J=1)/N(J=0) is 58 +/- 10
K. With the aid of ground-based data to calculate an appropriate
multi-component curve of growth, we have determined column densities for all
rotational levels up to J = 7. The J >= 2 states can be reasonably fitted with
a rotational excitation temperature of 307 +/- 23 K. Both the kinetic and
rotational temperatures are similar to those found in previous investigations
of diffuse clouds. The ratios of carbonaceous molecules to hydrogen molecules
are also similar to ratios in diffuse clouds, suggesting a similar chemistry
for this line of sight.


title:
The Palomar Abell Cluster Optical Survey I: Photometric Redshifts for
  431 Abell Clusters

abstract:
  This paper presents photometric redshifts for 431 Abell clusters imaged as
part of the Palomar Abell Cluster Optical Survey (PACOS), of which 236 are new
redshi fts. We have obtained moderately deep, 3--band (Gunn gri) imaging for
this sam ple at the Palomar Observatory 60'' telescope, as part of the
photometric calibration of DPOSS. Our data acquisition, reduction, and
photometric calibration techniques are described, and photometric accuracy and
consistency is demonstrated. An empirical redshift estimator is presented,
utilizing background-corrected median g-r colors and mean g magnitudes for the
ensemble of galaxies in each field. We present photometric redshift estimates
for the clusters in our sample with an accuracy of sigma_z=0.038. These
redshift estimates provide checks on single-galaxy cluster redshifts, as well
as distance information for studies of the Butcher-Oemler effect, luminosity
functions, M/L ratios, and many other projects.


title:
Far Ultraviolet Spectroscopic Explorer Observations of the Supernova
  Remnant N49 in the Large Magellanic Cloud

abstract:
  We report a Far Ultraviolet Spectroscopic Explorer satellite observation of
the supernova remnant N49 in the Large Magellanic Cloud, covering the 905 --
1187 A spectral region. A 30'' square aperture was used, resulting in a
velocity resolution of ~100 km/s. The purpose of the observation was to examine
several bright emission lines expected from earlier work and to demonstrate
diffuse source sensitivity by searching for faint lines never seen previously
in extragalactic supernova remnant UV spectra. Both goals were accomplished.
Strong emission lines of O VI 1031.9 A, 1037.6 A and C III 977.0 A were seen,
Doppler broadened to +/- 225 km/s and with centroids red-shifted to 350 km/s,
consistent with the LMC. Superimposed on the emission lines are absorptions by
C III and O VI 1031.9 at +260 km/s, which are attributed to warm and hot gas
(respectively) in the LMC. The O VI 1037.6 A line is more severely affected by
overlying interstellar and H2 absorption from both the LMC and our galaxy. N
III 989.8 A is not seen, but models indicate overlying absorption severely
attenuates this line. A number of faint lines from hot gas have also been
detected, many of which have never been seen in an extragalactic supernova
remnant spectrum.


title: Interstellar Gas in the NGC 4410 Galaxy Group

abstract:
  We present new radio continuum, 21 cm HI, and 2.6 mm CO data for the peculiar
radio galaxy NGC 4410A and its companion NGC 4410B, and compare with available
optical and X-ray maps. Our radio continuum maps show an asymmetric
double-lobedstructure, with a high surface brightness lobe extending 3.6 arcmin
(~100 kpc) to the southeast and a 6.2 arcmin (~180 kpc) low surface brightness
feature in the northwest. Molecular gas is abundant in NGC 4410A, with M(H2) ~
4 X 10^9 M(sun) (using the standard Galactic conversion factor), but is
undetected in NGC 4410B. HI is less abundant, with M(HI) ~ 10^9 M(sun) for the
pair. Our HI map shows a 3 X 10^8 M(sun) HI tail extending 1.7 arcmin (50 kpc)
to the southeast of the pair, coincident with a faint optical tail and
partially overlapping with the southeastern radio lobe. The HI tail is
anti-coincident with a 2' (56 kpc) long X-ray structure aligned with a stellar
bridge that connects the pair to a third galaxy. If this X-ray emission is
associated with the group, there is 3 - 8 X 10^8 M(sun) of hot gas in this
feature: either intracluster gas or shocked gas associated with the bridge. Our
detection of abundant interstellar gas in this pair suggests that the
distortions in this lobe map have been caused by the interstellar medium in
this system. The interaction of the two galaxies and the subsequent motion of
the interstellar medium in the system relative to the jet may have produced
sufficient ram pressure to bend the radio jet. An alternative hypothesis is
that the jet was distorted by ram pressure due to an intracluster medium,
although the small radial velocity of NGC 4410A relative to the group and the
lack of diffuse X-ray emission in the group makes this less likely unless the
group is not virialized or is in the process of merging with another group.


title: Redshift Distortions and Clustering in the PSCz Survey

abstract:
  We have constrained the redshift-distortion parameter $\beta \equiv
\Omega^{0.6}/b$ and the real-space power spectrum of the IRAS PSCz survey using
a spherical-harmonic redshift-distortion analysis combined with a data
compression method which is designed to deal with correlated parameters. Our
latest result, $\beta=0.4 \pm 0.1$, strongly rules out $\beta=1$.


title:
Lyman-alpha Forest Constraints on the Mass of Warm Dark Matter and the
  Shape of the Linear Power Spectrum

abstract:
  High resolution N-body simulations of cold dark matter (CDM) models predict
that galaxies and clusters have cuspy halos with excessive substructure.
Observations reveal smooth halos with central density cores. One possible
resolution of this conflict is that the dark matter is warm (WDM); this will
suppress the power spectrum on small scales. The Lyman-alpha forest is a
powerful probe of the linear power spectrum on these scales. We use
collisionless N-body simulations to follow the evolution of structure in WDM
models, and analyze artificial Lyman-alpha forest spectra extracted from them.
By requiring that there is enough small-scale power in the linear power
spectrum to reproduce the observed properties of the Lyman-alpha forest in
quasar spectra, we derive a lower limit to the mass of the WDM particle of 750
eV. This limit is robust to reasonable uncertainties in our assumption about
the temperature of the mean density gas (T0) at z=3. We argue that any model
that suppresses the CDM linear theory power spectrum more severely than a 750
eV WDM particle cannot produce the Lyman-alpha forest.


title: The Galactic Center He I Stars: Remains of a Dissolved Young Cluster?

abstract:
  A massive young star cluster, initially embedded in its parent molecular
cloud, will spiral into the Galactic Center from $\lta 30m_6^{1/2}\pc$ during
the life-time of its most massive stars, if the combined total mass is $\sim
10^6m_6\msun$. On its way inwards the system loses most of its mass to the
strong tidal field, until the dense cluster core of high-mass stars is finally
disrupted near the central black hole. A simple model is presented to argue
that this scenario may under plausible conditions explain the observed location
and rotation of the Galactic Center HeI stars. Accretion of star clusters into
the Galactic Center could be recurrent, and play an important role in
regulating the activity of Sgr A$^\ast$.


title:
ROSAT PSPC detection of soft X-ray absorption in GB 1428+4217: The most
  distant matter yet probed with X-ray spectroscopy

abstract:
  We report on a ROSAT PSPC observation of the highly-luminous z = 4.72
radio-loud quasar GB 1428+4217 obtained between 1998 December 11 and 17, the
final days of the ROSAT satellite. The low-energy sensitivity of the PSPC
detector was employed to constrain the intrinsic X-ray absorption of the
currently most distant X-ray detected object. Here we present the detection of
significant soft X-ray absorption towards GB 1428+4217, making the absorbing
material the most distant matter yet probed with X-ray spectroscopy. X-ray
variability by 25+-8 per cent is detected on a timescale of 6500 s in the rest
frame. The X-ray variation requires an unusually high radiative efficiency of
at least 4.2, further supporting the blazar nature of the source.


title:
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the
  Damped Ly-alpha galaxy at z_abs=3.3901

abstract:
  Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.


title: The Low Surface Brightness Extent of the Fornax Cluster

abstract:
  We have used a large format CCD camera to survey the nearby Fornax cluster
and its immediate environment for low luminosity low surface brightness
galaxies. Recent observations indicate that these are the most dark matter
dominated galaxies known and so they are likely to be a good tracer of the dark
matter in clusters. We have identified large numbers of these galaxies
consistent with a steep faint end slope of the luminosity function (alpha~ -2)
down to MB ~ -12. These galaxies contribute almost the same amount to the total
cluster light as the brighter galaxies and they have a spatial extent that is
some four times larger. They satisfy two of the important predictions of N-body
hierarchical simulations of structure formation using dark halos. The
luminosity (mass ?) function is steep and the mass distribution is more
extended than that defined by the brighter galaxies. We also find a large
concentration of low surface brightness galaxies around the nearby galaxy
NGC1291.


title: Electromagnetic Radiation and Motion of Dust Particle - A Simple Model

abstract:
  A simple model for motion of dust particle (meteoroid) under the action of
(solar) electromagnetic radiation is presented. The particle of the form of
plane mirror is taken into account and exact analytical results are presented.
As for long-term orbital evolution, particle may spiral outwards the central
body (Sun); initial conditions are important. As a consequence, motion of real
dust particles may differ from that generally considered.


title:
Data Streams from the Low Frequency Instrument On-Board the Planck
  Satellite: Statistical Analysis and Compression Efficiency

abstract:
  The expected data rate produced by the Low Frequency Instrument (LFI) planned
to fly on the ESA Planck mission in 2007, is over a factor 8 larger than the
bandwidth allowed by the spacecraft transmission system to download the LFI
data. We discuss the application of lossless compression to Planck/LFI data
streams in order to reduce the overall data flow. We perform both theoretical
analysis and experimental tests using realistically simulated data streams in
order to fix the statistical properties of the signal and the maximal
compression rate allowed by several lossless compression algorithms. We studied
the influence of signal composition and of acquisition parameters on the
compression rate Cr and develop a semiempirical formalism to account for it.
The best performing compressor tested up to now is the arithmetic compression
of order 1, designed for optimizing the compression of white noise like
signals, which allows an overall compression rate <Cr> = 2.65 +/- 0.02. We find
that such result is not improved by other lossless compressors, being the
signal almost white noise dominated. Lossless compression algorithms alone will
not solve the bandwidth problem but needs to be combined with other techniques.

categories: astro-ph cs.OH physics.data-an physics.space-ph


title:
On the transition to self-gravity in low mass AGN and YSO accretion
  discs

abstract:
  The equations governing the vertical structure of a stationary keplerian
accretion disc are presented. The model is based on the alpha-viscosity,
includes self-gravity, convective transport and turbulent pressure. A few
properties of the model are discussed for circumstellar and AGN discs.
  We show the strong sensitivity of the disc structure to the viscous energy
deposition towards the vertical axis, specially when entering inside the
self-gravitating part of the disc. The local version of the alpha-prescription
leads to a "singular" behavior which is also predicted by the vertically
averaged model. With respect, a much softer transition is observed with the
  "alpha-P" formalism. Turbulent pressure is important only for alpha > 0.1. It
lowers vertical density gradients, significantly thickens the disc, tends to
wash out density inversions and pushes the self-gravitating region to slightly
larger radii. Curves localizing the inner edge of the self-gravitating disc as
functions of the viscosity parameter and accretion rate are given. The lower
alpha, the closer to the center the self-gravitating regime, and the
sensitivity to the accretion rate is generally weak, except for alpha < 0.1.
This study suggests that models aiming to describe T-Tauri discs beyond about a
few to a few tens astronomical units from the central protostar using the
alpha-theory should consider vertical self-gravity. The Primitive Solar Nebula
was probably a bit (if not strongly) self-gravitating at the actual orbit of
giant planets. Alpha-discs hosted by active galaxies are self-gravitating
beyond about a thousand Schwarzchild radii. The inferred surface density
remains too high to lower the accretion time scale. More efficient mechanisms
driving accretion are required.


title: Monte Carlo Predictions of Far-Infrared Emission from Spiral Galaxies

abstract:
  We present simulations of Far Infrared (FIR) emission by dust in spiral
galaxies, based on the Monte Carlo radiative transfer code of Bianchi, Ferrara
& Giovanardi (1996). The radiative transfer is carried out at several
wavelength in the Ultraviolet, optical and Near Infrared, to cover the range of
the stellar Spectral Energy Distribution (SED). Together with the images of the
galactic model, a map of the energy absorbed by dust is produced. Using
Galactic dust properties, the spatial distribution of dust temperature is
derived under the assumption of thermal equilibrium. A correction is applied
for non-equilibrium emission in the Mid Infrared. Images of dust emission can
then be produced at any wavelength in the FIR.
  We show the application of the model to the spiral galaxy NGC 6946. The
observed stellar SED is used as input and models are produced for different
star-dust geometries. It is found that only optically thick dust disks can
reproduce the observed amount of FIR radiation. However, it is not possible to
reproduce the large FIR scalelength suggested by recent observation of spirals
at 200 um, even when the scalelength of the dust disk is larger than that for
stars. Optically thin models have ratios of optical/FIR scalelengths closer to
the 200um observations, but with smaller absolute scalelengths than optically
thick cases. The modelled temperature distributions are compatible with
observations of the Galaxy and other spirals. We finally discuss the
approximations of the model and the impact of a clumpy stellar and dust
structure on the FIR simulations.


title: Newtonian Limit of Induced Gravity

abstract:
  We discuss the weak-field limit of induced gravity and show that results
directly depend on the coupling and self-interaction potential of the scalar
field. A static spherically symmetric exact solution is found and its conformal
properties are studied. As an application, it is shown that the light
deflection angle and the microlensing quantities can be parametrized by the
coupling of the theory.


title: Instabilities and Clumping in Type Ia Supernova Remnants

abstract:
  We present two-dimensional high-resolution hydrodynamical simulations in
spherical polar coordinates of a Type Ia supernova interacting with a constant
density interstellar medium. The ejecta are assumed to be freely expanding with
an exponential density profile. The interaction gives rise to a double-shocked
structure susceptible to hydrodynamic instabilities. The Rayleigh-Taylor
instability initially grows, but the Kelvin-Helmholtz instability takes over,
producing vortex rings. The nonlinear instability initially evolves toward
longer wavelengths and eventually fades away when the reverse shock front is in
the flatter part of the supernova density distribution. Based on observations
of X-ray knots and the protrusion in the southeast outlin of Tycho's supernova
remnant, we include clumping in the ejecta. The clump interaction with the
reverse shock induces Rayleigh-Taylor and Kelvin-Helmholtz instabilities on the
clump surface that facilitate fragmentation. In order to survive crushing and
to have a bulging effect on the forward shock, the clump's initial density
ratio to the surrounding ejecta must be at least 100 for the conditions in
Tycho's remnant. The 56Ni bubble effect may be important for the development of
clumpiness in the ejecta. The observed presence of an Fe clump would then
require a non-radioactive origin for this Fe, possibly 54Fe. The large radial
distance of the X-ray emitting Si and S ejecta from the remnant center
indicates that they were initially in clumps.


title: The Intergalactic Medium

abstract:
  About half a million years after the Big Bang, the ever-fading cosmic
blackbody radiation cooled below 3000 K and shifted first into the infrared and
then into the radio, and the smooth baryonic plasma that filled the Universe
became neutral. The Universe then entered a ``dark age'' which persisted until
the first cosmic structures collapsed into gravitationally-bound systems, and
evolved into stars, galaxies, and black holes that lit up the Universe again.
Some time between redshift of 7 and 15, stars within protogalaxies created the
first heavy elements; these systems, together perhaps with an early population
of quasars, generated the ultraviolet radiation that reheated and reionized the
cosmos. The history of the Universe during and soon after these crucial
formative stages is recorded in the all-pervading intergalactic medium (IGM),
which is believed to contain most of the ordinary baryonic material left over
from the Big Bang. Throughout the epoch of structure formation, the IGM becomes
clumpy and acquires peculiar motions under the influence of gravity, and acts
as a source for the gas that gets accreted, cools, and forms stars within
galaxies, and as a sink for the metal enriched material, energy, and radiation
which they eject. Observations of absorption lines in quasar spectra at
redshifts up to 5 provide invaluable insight into the chemical composition of
the IGM and primordial density fluctuation spectrum of some of the earliest
formed cosmological structures, as well as of the ultraviolet background
radiation that ionizes them.


title: A new model of a tidally disrupted star

abstract:
  A new semi-analytical model of a star evolving in a tidal field is proposed.
The model is a generalization of the so-called 'affine' stellar model. In our
model the star is composed of elliptical shells with different parameters and
different orientations, depending on time and on the radial Lagrangian
coordinate of the shell. The evolution equations of this model are derived from
the virial relations under certain assumptions, and the integrals of motion are
identified. It is shown that the evolution equations can be deduced from a
variational principle. The evolution equations are solved numerically and
compared quantitatively with the results of 3D numerical computations of the
tidal interaction of a star with a supermassive black hole. The comparison
shows very good agreement between the main ``integral'' characteristics
describing the tidal interaction event in our model and in the 3D computations.
Our model is effectively a one-dimensional Lagrangian model from the point of
view of numerical computations, and therefore it can be evolved numerically
$10^{2}-10^{3}$ times faster than the 3D approach allows. This makes our model
well suited for intensive calculations covering the whole parameter space of
the problem.


title: Foreground and background dust in star cluster directions

abstract:
  This paper compares reddening values E(B-V) derived from the stellar content
of 103 old open clusters and 147 globular clusters of the Milky Way with those
derived from DIRBE/IRAS 100 micron dust emission in the same directions. Star
clusters at |b|> 20 show comparable reddening values between the two methods,
in agreement with the fact that most of them are located beyond the disk dust
layer. For very low galactic latitude lines of sight, differences occur in the
sense that DIRBE/IRAS reddening values can be substantially larger, suggesting
effects due to the depth distribution of the dust. The differences appear to
arise from dust in the background of the clusters consistent with a dust layer
where important extinction occurs up to distances from the Plane of ~ 300 pc.
For 3 % of the sample a significant background dust contribution might be
explained by higher dust clouds. We find evidence that the Milky Way dust lane
and higher dust clouds are similar to those of several edge-on spiral galaxies
recently studied in detail by means of CCD imaging.


title:
Introducing ZEUS-MP: A 3D, Parallel, Multiphysics Code for Astrophysical
  Fluid Dynamics

abstract:
  We describe ZEUS-MP: a Multi-Physics, Massively-Parallel, Message-Passing
code for astrophysical fluid dynamics simulations in 3 dimensions. ZEUS-MP is a
follow-on to the sequential ZEUS-2D and ZEUS-3D codes developed and
disseminated by the Laboratory for Computational Astrophysics
(lca.ncsa.uiuc.edu) at NCSA. V1.0 released 1/1/2000 includes the following
physics modules: ideal hydrodynamics, ideal MHD, and self-gravity. Future
releases will include flux-limited radiation diffusion, thermal heat
conduction, two-temperature plasma, and heating and cooling functions. The
covariant equations are cast on a moving Eulerian grid with Cartesian,
cylindrical, and spherical polar coordinates currently supported.
Parallelization is done by domain decomposition and implemented in F77 and MPI.
The code is portable across a wide range of platforms from networks of
workstations to massively parallel processors. Some parallel performance
results are presented as well as an application to turbulent star formation.


title:
Presupernova Evolution of Rotating Massive Stars II: -- Evolution of the
  Surface Properties

abstract:
  We investigate the evolution of the surface properties of models for rotating
massive stars, i.e., their luminosities, effective temperatures, surface
rotational velocities, and surface abundances of all isotopes, from the zero
age main sequence to the supernova stage. Our results are based on the grid of
stellar models by Heger, Langer, & Woosley, which covers solar metallicity
stars in the initial mass range 8 - 25 solar masses. Results are parameterized
by initial mass, initial rotational velocity and major uncertainties in the
treatment of the rotational mixing inside massive stars.
  Rotationally induced mixing processes widen the main sequence and increase
the core hydrogen burning lifetime, similar to the effects of convective
overshooting. It can also significantly increase the luminosity during and
after core hydrogen burning, and strongly affects the evolution of the
effective temperature. Our models predict surface rotational velocities for
various evolutionary stages, in particular for blue supergiants, red
supergiants, and for the immediate presupernova stage.
  We discuss the changes of the surface abundances due to rotationally induced
mixing for main sequence and post main sequence stars. We single out two
characteristics by which the effect of rotational mixing can be distinguished
from that of massive close binary mass transfer, the only alternative process
leading to non-standard chemical surface abundances in massive stars. A
comparison with observed abundance anomalies in various types of massive stars
supports the concept of rotational mixing in massive stars and indicates that
it is responsible for most of the observed abundance anomalies.


title: A New Perspective on Cosmic Coincidence Problems

abstract:
  Cosmological data suggest that we live in an interesting period in the
history of the universe when \rho_\Lambda \sim \rho_M \sim \rho_R. The
occurence of any epoch with such a "triple coincidence" is puzzling, while the
question of why we happen to live during this special epoch is the "Why now?"
problem. We introduce a framework which makes the triple coincidence
inevitable; furthermore, the ``Why now?'' problem is transformed and greatly
ameliorated. The framework assumes that the only relevant mass scales are the
electroweak scale, M_{EW}, and the Planck scale, M_{Pl}, and requires
\rho_\Lambda^{1/4} \sim M_{EW}^2/M_{Pl} parametrically. Assuming that the true
vacuum energy vanishes, we present a simple model where a false vacuum energy
yields a cosmological constant of this form.


title:
A Determination of the Hubble Constant from Cepheid Distances and a
  Model of the Local Peculiar Velocity Field

abstract:
  We present a measurement of the Hubble Constant based on Cepheid distances to
27 galaxies within 20 Mpc. We take the Cepheid data from published measurements
by the Hubble Telescope Key Project on the Distance Scale (H0KP). We calibrate
the Cepheid Period-Luminosity (PL) relation with data from over 700 Cepheids in
the LMC obtained by the OGLE collaboration; we assume an LMC distance modulus
of 18.50 mag (d=50.1 kpc). Using this PL calibration we obtain new distances to
the H0KP galaxies. We correct the redshifts of these galaxies for peculiar
velocities using two distinct velocity field models: the phenomenological model
of Tonry et al. and a model based on the IRAS density field and linear
gravitational instability theory. We combine the Cepheid distances with the
corrected redshifts for the 27 galaxies to derive H_0, the Hubble constant. The
results are H_0 = 85 +/- 5 km/s/Mpc (random error) at 95% confidence when the
IRAS model is used, and 92 +/- 5 km/s/Mpc when the phenomenological model is
used. The IRAS model is a better fit to the data and the Hubble constant it
returns is more reliable. Systematic error stems mainly from LMC distance
uncertainty which is not directly addressed by this paper. Our value of H_0 is
significantly larger than that quoted by the H0KP, H_0 = 71 +/- 6 km/s/Mpc.
Cepheid recalibration explains ~30% of this difference, velocity field analysis
accounts for ~70%. We discuss in detail possible reasons for this discrepancy
and future study needed to resolve it.


title:
Abundances of Stars in the Galactic Bulge Obtained Using the Keck
  Telescope

abstract:
  We report on detailed abundances of giants in the Galactic bulge, measured
with the HIRES echelle spectrograph on the 10-m Keck telescope. We also review
other work on the bulge field population and globular clusters using
Keck/HIRES. Our new spectra have 3 times the resolution and higher S/N than
previous spectra obtained with 4m telescopes. We are able to derive $\log g$
from Fe II lines and excitation temperature from Fe I lines, and do not rely on
photometric estimates for these parameters. We confirm that the iron abundance
range extends from -1.6 to +0.55 dex. The improved resolution and S/N of the
Keck spectra give [Fe/H] typically 0.1 to 0.2 dex higher than previous studies
of bulge stars more metal rich than the Sun. Alpha elements are enhanced even
for stars at the Solar metallicity (as is the case for bulge globular
clusters). We confirm our earlier abundance ananlysis of bulge giants and find
that Mg and Ti are enhanced relative to Ca and Si even up to [Fe/H]=+0.55. We
also resport the first reliable estimates of the bulge oxygen abundance. Our
element ratios confirm that bulge giants have a clearly identifiable chemical
signature and suggest a rapid formation timescale for the bulge.


title: Decaying neutrino and a high cosmological baryon density

abstract:
  The low second acoustic peak in the recent Boomerang data may indicate a
cosmological baryon density which is larger than allowed by standard big bang
nucleosynthesis.
  We show that the decay of the tau-neutrino: nu_tau -> nu_e + phi, where nu_e
is the electron neutrino and phi is a scalar, essentially can assure agreement
between BBN calculations and light element observations for a large baryon
density.


title: Cosmic strings in the age of Boomerang

abstract:
  We show how two simple modifications to the standard cosmic string scenario
for structure formation compare to the recently released Boomerang data set.
Namely we consider pure string closed models and mixed models where both
inflation and strings are responsible for the perturbations. In the closed
models we find that pure string models would require a universe with roughly
$\Omega_M=0.8$, $\Omega_{\Lambda}=1.6$ to agree with the peak position revealed
by the data and in agreement with the SNIa data. In the hybrid scenario with
local strings we find that we require even more tilt and baryon content
($n_s\sim 0.8$, $\Omega_b=0.08$, $H_0=70$) to match the data than with pure
inflation models. The case with global strings fares better with a standard
period of $\Lambda$CDM inflation and a $\sim30%$ contribution from strings
being in good agreement with the data.


title: The neutrino star in the bulk Universe

abstract:
  Motivated by the Kaluza-Klein theory with large extra spacetime dimensions
the neutrino star built from the massive sterile neutrinos core and the
massless brane neutrinos envelope is presented. The six - dimensional
compactification scale ~15 MeV gives the maximal neutrino mass M_max = 2.3 10^4
of the solar mass with the radius R_max = 1.2 10^6 km . The maximal neutrino
star parameters varies with temperature. In the limit of the neutrino ball
approximation the maximal sterile neutrino star is M_max = 1.1 10^6 of the
solar mass.


title: Semiclassical planetology : some results

abstract:
  The aim of this lecture is to review the basic physical ideas and some
planetological results of the semiclassical theory of dense matter proposed by
P.Savic and R.Kasanin


title:
On the bolometric quiescent luminosity and luminosity swing of black
  hole candidate and neutron star low mass X-ray transients

abstract:
  Low mass X-ray transients (LMXRTs) hosting black hole candidates (BHCs)
display on average a factor of ~100 larger swing in the minimum (quiescent) to
maximum (outburst) X-ray luminosity than neutron stars (NSs), despite the fact
that the swing in the mass inflow rate is likely in the same range. Advection
dominated accretion flows (ADAFs) were proposed to interpret such a difference.
The residual optical/UV emission of quiescent LMXRTs, after subtraction of the
companion star spectrum, is produced by synchrotron radiation in the (latest
version) of ADAF and therefore is part of the ADAF's luminosity budget. We
demonstrate that, once the residual optical/UV emission is taken into account,
the bolometric luminosity swing of BHCs is consistent with that of NSs. We
explore here an alternative scenario to ADAFs in which very little mass
accretion onto the collapsed star takes place in the quiescence intervals. The
residual optical/UV emission of BHCs are expected to derive from the energy
released by the matter transferred from the companion star at radii comparable
to the circularisation radius. The quiescent X-ray luminosity originates either
from accretion onto the BH at very low rates and/or from coronal activity in
the companion star or in the outer disk. For comparably small mass inflow
rates, the NSs in these systems are likely in the radio pulsar regime. In the
interaction of the radio pulsar relativistic wind with matter transferred from
the companion star, a shock forms, the power law-like emission of which powers
both the harder X-ray emission and most of the residual optical/UV. The soft,
thermal-like X-ray component may arise from the cooling of the NS surface. This
scenario matches well both the X-ray and bolometric luminosity swing of LMXRTs.
(ABRIDGED).


title: Particle Heating by Nonlinear Alfvenic Turbulence in ADAFs

abstract:
  Particle heating in advection-dominated accretion flows (ADAFs) by nonlinear
MHD (Alfvenic) turbulence is investigated. Such turbulence with
highly-fluctuating magnetic fields, $\tilde B\sim B_0$, is believed to be
naturally produced by the magnetic shearing instability near the nonlinear
saturation. It is shown that the energy is dissipated in the parallel cascade,
which occurs due to nonlinear compressibility of high-amplitude turbulence, and
predominantly heats protons, but not electrons. The conservative limit on the
electron--to--proton heating fraction is $\delta\lesssim{\rm
few}\times10^{-2}$.


title:
The Mass Assembly and Star Formation Characteristics of Field Galaxies
  of Known Morphology

abstract:
  We discuss a new method for inferring the stellar mass of a distant galaxy of
known redshift based on the combination of a near-infrared luminosity and
multi-band optical photometry. The typical uncertainty for field galaxies with
I<22 in the redshift range 0<z<1 is a factor 2. We apply this method to a
newly-constructed sample of 321 field galaxies with redshifts and Hubble Space
Telescope morphologies enabling us to construct the stellar mass density
associated with various morphologies as a function of redshift. We find a
marked decline with time in the stellar mass associated with peculiar galaxies
accompanied by a modest rise in that observed for ellipticals. The result
suggests that peculiars decline in abundance because they transform and merge
into regular systems. The star formation rate per unit stellar mass indicates
that massive systems completed the bulk of their star formation before redshift
one, whereas dwarfs continue to undergo major episodes of activity until the
present epoch.


title: The Origin of the Solar Flare Waiting-Time Distribution

abstract:
  It was recently pointed out that the distribution of times between solar
flares (the flare waiting-time distribution) follows a power law, for long
waiting times. Based on 25 years of soft X-ray flares observed by Geostationary
Operational Environmental Satellite (GOES) instruments it is shown that 1. the
waiting-time distribution of flares is consistent with a time-dependent Poisson
process, and 2. the fraction of time the Sun spends with different flaring
rates approximately follows an exponential distribution. The second result is a
new phenomenological law for flares. It is shown analytically how the observed
power-law behavior of the waiting times originates in the exponential
distribution of flaring rates. These results are argued to be consistent with a
non-stationary avalanche model for flares.


title: Imaging of Ultraluminous Infrared Galaxies in the Near-UV

abstract:
  We present the first ground-based U' (3410 angstroms) images of Ultraluminous
Infrared Galaxies (ULIGs). Strong U' emission (median total M_U' = -20.8) is
seen in all systems and in some cases the extended tidal features (both the
smooth stellar distribution and compact star-forming features) contribute up to
60-80% of the total flux. The star-forming regions in both samples are found to
have ages based on spectral synthesis models in the range 10-100 Myrs, and most
differences in color between them can be attributed to the effects of dust
reddening. Additionally, it is found that star-formation in compact knots in
the tidal tails is most prominent in those ULIGs which have double nuclei,
suggesting that the star-formation rate in the tails peaks prior to the actual
coalescence of the galaxy nuclei and diminishes quickly thereafter. Similar to
results at other wavelengths, the observed star formation at U' can only
account for a small fraction of the known bolometric luminosity of the ULIGs.
Azimuthally averaged radial light profiles at U' are characterized by a sersic
law with index n=2, which is intermediate between an exponential disk and an
r^(-1/4) law and closely resembles the latter at large radii. The implications
of this near-ultraviolet imaging for optical/near-infrared observations of high
redshift counterparts of ULIGs are discussed.


title:
MAXIMA-1: A Measurement of the Cosmic Microwave Background Anisotropy on
  angular scales of 10 arcminutes to 5 degrees

abstract:
  We present a map and an angular power spectrum of the anisotropy of the
cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a
balloon-borne experiment with an array of 16 bolometric photometers operated at
100 mK. MAXIMA observed a 124 square degrees region of the sky with 10
arcminute resolution at frequencies of 150, 240 and 410 GHz. The data were
calibrated using in-flight measurements of the CMB dipole anisotropy. A map of
the CMB anisotropy was produced from three 150 and one 240 GHz photometer
without need for foreground subtractions. Analysis of this CMB map yields a
power spectrum for the CMB anisotropy over the range 36 < l < 785. The spectrum
shows a peak with an amplitude of 78 +/- 6 micro-Kelvin at l ~ 220 and an
amplitude varying between ~40 micro-Kelvin and ~50 micro-Kelvin for 400 < l <
785.


title: Constraints on Cosmological Parameters from MAXIMA-1

abstract:
  We set new constraints on a seven-dimensional space of cosmological
parameters within the class of inflationary adiabatic models. We use the
angular power spectrum of the cosmic microwave background measured over a wide
range of \ell in the first flight of the MAXIMA balloon-borne experiment
(MAXIMA-1) and the low \ell results from COBE/DMR. We find constraints on the
total energy density of the universe, \Omega=1.0^{+0.15}_{-0.30}, the physical
density of baryons, \Omega_{b}h^2=0.03 +/- 0.01, the physical density of cold
dark matter, \Omega_{cdm}h^2=0.2^{+0.2}_{-0.1}$, and the spectral index of
primordial scalar fluctuations, n_s=1.08+/-0.1, all at the 95% confidence
level. By combining our results with measurements of high-redshift supernovae
we constrain the value of the cosmological constant and the fractional amount
of pressureless matter in the universe to 0.45<\Omega_\Lambda<0.75 and
0.25<\Omega_{m}<0.50, at the 95% confidence level. Our results are consistent
with a flat universe and the shape parameter deduced from large scale
structure, and in marginal agreement with the baryon density from big bang
nucleosynthesis.


title: Narrow-Line Seyfert 1s: 15 Years Later

abstract:
  The spectroscopic properties of the objects that came to be called
Narrow-Line Seyfert 1s were first systematically described and named as such 15
years ago by Osterbrock & Pogge (1985). At the time, they were a relatively
rare and peculiar subclass of Seyfert galaxies. Their discovery in large
numbers in X-ray surveys, however, has elevated them to a role as important
members of the AGN family, ones which may hold many keys to understanding the
physics of AGN across the electromagnetic spectrum. This contribution reviews
the spectral classification of the narrow-line Seyfert 1s, and describes some
of the properties that make this unusual class of objects interesting.


title: The BeppoSAX view of NLS1s

abstract:
  The main results of broad-band (0.1-10 keV) BeppoSAX observations of a
selected sample of NLS1s are presented and discussed. It is shown that all the
available data are consistent with a scenario in which NLS1s are running at a
high accretion rate.


title: ROSAT Results on Narrow-Line Seyfert 1 Galaxies

abstract:
  The excellent soft X-ray sensitivity of the PSPC detector onboard the ROSAT
satellite provided the first chance to study precisely the spectral and timing
properties of Narrow-Line Seyfert 1 galaxies. ROSAT observations of Narrow-Line
Seyfert 1 galaxies have revealed (1) the existence of a giant soft X-ray
excess, (2) a striking, clear correlation between the strength of the soft
X-ray excess emission and the FWHM of the H-beta line, (3) the general absence
of significant soft X-ray absorption by neutral hydrogen above the Galactic
column, (4) short doubling time scales down to about 1000 seconds, (5) the
existence of persistent giant (above a factor of 10), and rapid (less than 1
day) X-ray variability in extragalactic sources. The soft X-ray results on
Narrow-Line Seyfert 1 galaxies indicate that their black hole regions are
directly visible, further supporting the Seyfert 1 nature of these objects. The
extreme X-ray properties of Narrow-Line Seyfert 1 galaxies make them ideal
objects for understanding many of the problems raised generally by the Seyfert
phenomenon.


title:
ASCA Observations of NLS1s: BH Mass Estimation from X-ray Variability
  and X-ray Spectra

abstract:
  ASCA observations of Narrow-Line Seyfert 1 galaxies (NLS1s) are presented. We
focus on the black hole size of the NLS1 sources by employing two independent
methods for the mass estimation; one is using X-ray variability, the other is
using a blackbody fit to the soft component. Although the coincidence is not
good for some sources, the mass estimated by these methods ranges from 1e5 to
1e7 solar masses, systematically smaller than those for typical (broad line)
Seyfert 1. We consider the small mass black hole to be the principal cause of
the several extreme characteristics of the NLS1s.


title: ASCA Observations of NLS1s

abstract:
  The study of NLS1s using ASCA has many advantages. A representative sample
can be studied; to date, observations of more than 30 NLS1s have been made.
ASCA observations are conducted contiguously, so their X-ray variability
properties can be studied systematically. ASCA detectors have a broad band pass
and moderate energy resolution, properties which allow their complex X-ray
spectrum to be deconvolved. ASCA observations have revealed that a soft excess
extending up to 1 keV is frequently found in the X-ray spectra from NLS1s. The
hard X-ray photon index has been shown to be systematically steeper than in
Seyfert 1 galaxies with broad optical lines. NLS1s also exhibit larger
amplitude variability than broad-line Seyferts of similar hard X-ray
luminosity. On occasion, features in the soft X-ray band have been detected
that appear to be specific to NLS1s; ionized iron lines have also been
observed. These results have been fundamental for building our current picture
of the X-ray emission from NLS1s. Many of the properties can be explained if
the specific accretion rate is larger in NLS1s than in Seyfert 1 galaxies with
broad optical lines. NLS1s may exemplify an extreme state of an intrinsic
physical parameter and therefore their study may lead to an enhanced
understanding of AGN in general. This proceedings contribution has two parts.
First I describe and discuss some of the results obtained from a study of the
X-ray variability in NLS1s using ASCA data (Leighly 1999ab). Then, I discuss
the results from our HST observations of NLS1s that were first presented during
this meeting (Leighly & Halpern 2000).


title: Black Holes and Host Galaxies of NLS1s

abstract:
  Recently, reliable mass estimates for the central black holes in AGN became
feasible due to emission-line reverberation techniques. Using this method as a
calibrator, it is possible to determine black hole masses for a wide range of
AGN, in particular NLS1s. Do NLS1s have smaller black holes than ordinary
Seyfert 1 galaxies? Are their black holes smaller compared to the sizes of
their host galaxies? Do they have larger L/M ratios? Do NLS1s have hotter
accretion disks? I confront these questions with accretion disk theory and with
the data, showing that the above may well be the case.