title: Entropic-Acoustic instability in shocked accretion flows

abstract:
  A new instability mechanism is described in accretion flows where the gas is
accelerated from a stationary shock to a sonic surface. The instability is
based on a cycle of acoustic and entropic waves in this subsonic region of the
flow. When advected adiabatically inward, entropy perturbations trigger
acoustic waves propagating outward. If a shock is present at the outer
boundary, acoustic waves reaching the shock produce new entropy perturbations,
thus creating an entropic-acoustic cycle between the shock and the sonic
surface. The interplay of acoustic and entropy perturbations is estimated
analytically using a simplified model based on the compact nozzle
approximation. According to this model, the entropic-acoustic cycle is unstable
if the sound speed at the sonic surface significantly exceeds the sound speed
immediately after the shock. The growth rate scales like the inverse of the
advection time from the outer shock to the sonic point. The frequency of the
most unstable perturbations is comparable to the refraction cutoff, defined as
the frequency below which acoustic waves propagating inward are significantly
refracted outward. This generic mechanism should occur in Bondi-Hoyle-Lyttleton
accretion, and also in shocked accretion discs.


title: An Atlas of Burst Oscillations and Spectral Properties in 4U 1728-34

abstract:
  We study correlations between the burst properties and the position in the
color-color diagram of the low mass X-ray binary 4U 1728-34 using 21 bursts
found in two data sets obtained with the Rossi X-ray Timing Explorer. Using
spectral fits we analyze the spectral evolution during the bursts and determine
the burst peak flux, temperature, rise time and fluence. Using dynamical power
spectra we study the properties of the ~363 Hz burst oscillations. We find
correlations between fluence, peak flux, the occurrence of radius expansion and
the presence of burst oscillations, and the position of the source in the
color-color diagram. The radius expansion bursts with and without burst
oscillations differ both with respect to where they occur in the color-color
diagram and in how the radius expansion takes place. We compare our results
with those of a similar study by Muno et al. (2000) for KS 1731-26. Both KS
1731-260 and 4U 1728-34 show more or less the same behavior with respect to the
dependence of the presence/absence of the burst oscillations on the position of
the source in the color-color diagram, but the dependence of most of the
spectral burst parameters on the position in the color-color diagram is clearly
different. We find that the systematic absence in 4U 1728-34 of burst
oscillations in the ``island'' state of the color-color diagram is not
explained by the bursts involving mixed H-He burning, as may be the case in KS
1731--260 (Cumming & Bildsten 2000).


title: A ridge of recent massive star formation between Sgr B2M and Sgr B2N

abstract:
  We present single dish and interferometric maps of several rotational
transitions of HC3N vibrationally excited levels towards Sgr B2. The single
dish maps show, for the first time, new four bright clumps (Sgr B2R1 to B2R4)
in the ridge connecting the main cores Sgr B2M and Sgr B2N, and a low
brightness extended region to the west of the ridge (Sgr B2W). The physical
properties and the kinematics of all hot cores have been derived from the HC3N*
lines. Our high angular resolution images show that the Sgr B2N hot core breaks
in two different hot cores, Sgr B2N1 and N2, with different radial velocities
and separated by 2 arcsec in declination. We find that the excitation of the
HC3N* emission in all hot cores can be represented by a single temperature and
that the linewidth of the HC3N* rotational lines arising from different
vibrational levels systematically decreases as the energy of the vibrational
level increases. The systematic trend in the linewidth is likely related to the
increase of the velocity as the distance to the exciting source increases. The
different HC3N abundances in the hot cores reflect different stages of
evolution due to time dependent chemistry and/or photo-dissociation by UV
radiation from nearby HII regions. We propose that Sgr B2M and B2N contain a
cluster of 20-30 hot cores and that the Sgr B2R1-B2R4 hot cores represent
isolated formation of massive stars.


title:
From Globular Clusters to Tidal Dwarfs: Structure Formation in Tidal
  Tails

abstract:
  Star clusters can be found in galaxy mergers, not only in central regions,
but also in the tidal debris. In both the Eastern and Western tidal tails of
NGC 3256 there are dozens of young star clusters, confirmed by their blue
colors and larger concentration index as compared to sources off of the tail.
Tidal tails of other galaxy pairs do not have such widespread cluster
formation, indicating environmental influences on the process of star formation
or the packaging of the stars.


title:
Probing the Structure of Dark Matter in Galaxy Halos and Clusters using
  Supernovae

abstract:
  A new method for measuring gravitational lensing with high redshift type Ia
supernovae is investigated. The method utilizes correlations between foreground
galaxies and supernova brightnesses to substantially reduce possible systematic
errors and increase the signal to noise ratio. It is shown that this lensing
signal can be related to the mass, size and substructure of galaxy halos and
galaxy clusters if dark matter consists of microscopic particles. This
technique may be particularly useful for measuring the size of dark matter
halos, a measurement to which the lensing of galaxies is not well suited, and
for measuring the level of substructure in galaxy halos, a problematic
prediction of the cold dark matter model. The contributions to the signal from
galaxy halos and galaxy clusters are modeled and contributions to the noise
from fluctuations in the galaxy number counts, galaxy redshift error,
dispersion in SN luminosities and sample variance are estimated. The intrinsic
distribution of supernova luminosities and its redshift evolution are removed
as major sources of uncertainty. The method is found to be complimentary to
galaxy--galaxy lensing. The required observations of $\simgt 100$ supernovae
have already been proposed for the purposes of cosmological parameter
estimation.


title: Adaptive optics imaging of P Cygni in Halpha

abstract:
  We obtained Halpha diffraction limited data of the LBV star P Cyg using the
ONERA Adaptive Optics (AO) facility BOA at the OHP 1.52m telescope on October
1997. Taking P Cyg and the reference star 59 Cyg AO long exposures we find that
P Cyg clearly exhibits a large and diffuse intensity distribution compared to
the 59 Cyg's point-like source. A deconvolution of P Cyg using 59 Cyg as the
Point Spread Function was performed by means of the Richardson-Lucy algorithm.
P Cyg clearly appears as an unresolved star surrounded by a clumped envelope.
The reconstructed image of P Cyg is compared to similar spatial resolution maps
obtained from radio aperture synthesis imaging. We put independent constraints
on the physics of P Cyg which agree well with radio results. We discuss future
possibilities to constrain the wind structure of P Cyg by using
multi-resolution imaging, coronagraphy and long baseline interferometry to
trace back its evolutionary status.


title:
Chandra study of an overdensity of X-ray sources around two distant
  (z~0.5) clusters

abstract:
  We present results from a Chandra X-ray Observatory study of the field X-ray
source populations in 4 different observations: two high-redshift (z~0.5)
clusters of galaxies 3C295 and RXJ003033.2+261819; and two non-cluster fields
with similar exposure time. Surprisingly, the 0.5-2 keV source surface
densities (~900-1200 sources deg**-2 at a flux limit of 1.5x10**-15 erg
cm**-2s**-1) measured in an ~8'x8' area surrounding each cluster exceed by a
factor of ~2 the value expected on the basis of the ROSAT and Chandra
logN-logS, with a significance of ~2 sigma each, or ~3.5 sigma when the 2
fields are combined (i.e. a probability to be a statistical fluctuation of <1%
and <0.04%, respectively). The same analysis performed on the non-cluster
fields and on the outer chips of the cluster fields does NOT show evidence of
such an excess. In both cluster fields, the summed 0.5-10 keV spectrum of the
detected objects is well fitted by a power-law with Gamma~1.7 similar to AGNs
and shows no sign of intrinsic absorption. The few (~10 out of 35) optical
identifications available to date confirm that most of them are, as expected,
AGNs but the number of redshifts available is too small to allow conclusions on
their nature. We discuss possible interpretations of the overdensity in terms
of: a statistical variation of Cosmic Background sources; a concentration of
AGNs and/or powerful starburst galaxies associated with the clusters; and g
ravitational lensing of background QSO's by the galaxy clusters. All
explanations are however difficult to reconcile with the large number of excess
sources detected. Deeper X-ray observations and more redshifts measurements are
clearly required to settle the issue.


title:
Black hole masses from power density spectra: determinations and
  consequences

abstract:
  We analyze the scaling of the X-ray power density spectra with the mass of
the black hole on the example of Cyg X-1 and Seyfert 1 galaxy NGC 5548. We show
that the high frequency tail of the power density spectrum can be successfully
used for determination of the black hole mass. We determine the masses of the
black holes in 6 Broad Line Seyfert 1 galaxies, 5 Narrow Line Seyfert 1
galaxies and two QSOs using available power density spectra. The proposed
scaling is clearly appropriate for other Seyfert galaxies and QSOs. In all but
1 normal Seyferts the resulting luminosity to the Eddington luminosity ratio is
smaller than 0.15, with a source MCG -6-15-30 being an exception. The
applicability of the same scaling to Narrow Line Seyfert 1 is less clear and
there may be a systematic shift between the power spectra of NLS1 and S1
galaxies of the same mass, leading to underestimation of the black hole mass.
However, both the method based on variability and the method based on spectral
fitting show that those galaxies have relatively low masses and high luminosity
to the Eddington luminosity ratio, supporting the view of those objects as
analogs of galactic sources in their high/soft or very high state based on the
overall spectral shape. Bulge masses of their host galaxies are similar to
normal Seyfert galaxies so they do not follow the black hole mass-bulge mass
relation for Seyfert galaxies, being evolutionary less advanced, as suggested
by Mathur (2000). The bulge mass-black hole mass relation in our sample is
consistent with being linear, with black hole to bulge ratio $\sim$ 0.03 %,
similar to Wandel (1999) and Laor (1998, 2001) for low mass objects but
significantly shifted from the relation of Magorrian et al. (1998) and McLure &
Dunlop (2000).


title:
The Luminosity Function of Magnitude and Proper-Motion Selected Samples.
  The case of White-Dwarfs

abstract:
  The luminosity function of white dwarfs is a powerful tool for studies of the
evolution and formation of the Milky Way. The (theoretical) white dwarf cooling
sequence provides a useful indicator of the evolutionary time scales involved
in the chronometry and star formation history of the galactic disk, therefore,
intrinsically faint (& old) white dwarfs in the immediate solar neighborhood
can be used to determine an upper limit for the age of the galactic disk.
  In this paper we examine the faint-end ($M_V > +14$) behavior of the disk
white dwarf luminosity function using the $1/V_{\rm max}$ method, but fully
including the effects of realistic observational errors in the derived
luminosity function. We employ a Monte Carlo approach to produce many different
realizations of the luminosity function from a given data set with
pre-specified and reasonable errors in apparent magnitude, proper-motions,
parallaxes and bolometric corrections. These realizations allow us to compute
both a mean and an expected range in the luminosity function that is compatible
with the observational errors.
  We find that current state-of-the art observational errors, mostly in the
bolometric corrections and trigonometric parallaxes, play a major role in
obliterating (real or artificial) small scale fluctuations in the luminosity
function. We also find that a better estimator of the true luminosity function
seems to be the median over simulations, rather than the mean. When using the
latter, an age for the disk of 10 Gyr or older can not be ruled out from the
sample of Leggett, Ruiz, and Bergeron (1998).


title: ASCA and other contemporaneous observations of the blazar B2 1308+326

abstract:
  The high redshift (z=0.997) blazar B2 1308+326 was observed contemporaneously
at x-ray, optical and radio wavelengths in June 1996. The x-ray observations
were performed with ASCA. The ASCA results were found to be consistent with
reanalysed data from two earlier ROSAT observations. The combined ASCA and
ROSAT data reveal an x-ray spectrum that is best fit by a broken power law with
absorber model. The break in the x-ray spectrum is interpreted, to be the
emerging importance of inverse Compton (IC) emission which dominates the ASCA
spectrum. The faint optical state reported for these observations
(m_V=18.3+/-0.25) is incompatible with the high synchrotron flux previously
detected by ROSAT. The IC emission detected by both ROSAT and ASCA was not
significantly affected by the large change in the synchrotron component. MgII
emission was detected with an equivalent width (EW) significantly different
from previously reported values. Absorption at a level of in excess of the
Galactic value was detected, indicating the possible presence of a foreground
absorber. A gravitational microlensing scenario cannot therefore be ruled out
for this blazar. B2 1308+326 could be a typical radio-selected BL Lac in terms
of peak synchrotron frequency and optical and radio variability but its high
bolometric luminosity, variable line emission and high Doppler boost factor
make it appear more like a quasar than a BL Lac. It is suggested that B2
1308+326 be considered as the prototype of this class of composite source.


title: The Cluster of Galaxies Abell 970

abstract:
  We present a dynamical analysis of the galaxy cluster Abell 970 based on a
new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence
observatories. Our analysis indicates that this cluster has a substructure and
is out of dynamical equilibrium. This conclusion is also supported by
differences in the positions of the peaks of the surface density distribution
and X-ray emission, as well as by the evidence of a large scale velocity
gradient in the cluster. We also found a discrepancy between the masses
inferred with the virial theorem and with the X-ray emission, what is expected
if the galaxies and the gas inside the cluster are not in hydrostatic
equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out
of equilibrium as suggested by Allen (1998). We propose that cooling flows may
have an intermittent behavior, with phases of massive cooling flows being
followed by phases without significant cooling flows after the acretion of a
galaxy group massive enough to disrupt the dynamical equilibrium in the center
of the clusters. A massive cooling flow will be established again, after a new
equilibrium is achieved.


title:
A Time Varying Strong Coupling Constant as a Model of Inflationary
  Universe

abstract:
  We consider a scenario where the strong coupling constant was changing in the
early universe. We attribute this change to a variation in the colour charge
within a Bekenstein-like model. Treating the vacuum gluon condensate $<G^2>$ as
a free paramete r, we could generate inflation with the required properties to
solve the fluctuation and other standard cosmology problems. A possible
approach to end the inflation is suggested.


title: The Arecibo OH Megamaser Survey and the Galaxy Merger Rate

abstract:
  We present the current results of a survey for OH megamasers (OHMs) underway
at the Arecibo Observatory. The survey is 2/3 complete and has produced a high
OHM detection rate (1 in 6) from a redshift-selected sample of IRAS galaxies.
The survey will relate the OHM luminosity function to the galaxy merger rate,
allowing subsequent blind OHM surveys to measure the galaxy merger rate as a
function of cosmic time. The survey has also made the first detection of strong
variability in OHMs. Variability will provide a powerful tool for understanding
the small-scale physical settings and mechanisms of OHMs.


title:
The interplay of observational errors through numerical simulations
  using the $1/V_{\rm max}$ method for magnitude and proper-motion samples of
  local disk white dwarfs.}

abstract:
  White dwarf cooling sequences provides a useful indicator of the evolutionary
time scales involved in the chronometry and star formation history of the
galactic disk and, for this reason, the luminosity function of white dwarfs has
become a powerful tool for studies of the evolution and formation of the Milky
Way.
  We examine the faint-end ($M_V > +14$) behavior of the disk white dwarf
luminosity function using the $1/V_{\rm max}$ method, but, for the first time,
fully including the effects of realistic observational errors in the derived
luminosity function.
  We find that observational errors, mostly in the bolometric corrections and
trigonometric parallaxes, play a major role in obliterating (real or
artificial) small scale fluctuations in the luminosity function. A better
estimator of the true luminosity function seems to be the median over
simulations, rather than the mean. When using the latter, an age of 10 Gyr or
older can not be ruled out from the sample of Leggett, Ruiz, and Bergeron
(1998).


title: Luminous hot accretion disks

abstract:
  We find a new two-temperature hot branch of equilibrium solutions for
stationary accretion disks around black holes. In units of Eddington accretion
rate defined as $10L_{\rm Edd}/c^2$, the accretion rates to which these
solutions correspond are within the range $\dot{m}_1 \la \dot{m} \la 1$, here
$\dot{m}_1$ is the critical rate of advecti$. In these solutions, the energy
loss rate of the ions by Coulomb energy transfer between the ions and electrons
is larger than the viscously heating rate and it is the advective heating
together with the viscous dissipation that balances the Coulomb cooling of
ions. When $\dot{m}_1 \la \dot{m} \la \dot{m}_2$, where $\dot{m}_2 \sim 5
\dot{m}_1 < 1$, the accretion flow remains hot throughout the disk. When
$\dot{m}_2 \la \dot{m}\la 1$, Coulomb interaction will cool the inner region of
the disk within a certain radius ($r_{\rm tr} \sim$ several -- tens of
Schwarzschild radii or larger depending on the accretion rate and the outer
boundary condition) and the disk will collapse onto the equatorial plane and
form an optically thick cold annulus. Compared to ADAF, these hot solutions are
much more luminous because of the high accretion rate and efficiency,
therefore, we name them luminous hot accretion disks.


title: Modeling Mid-Ultraviolet Spectra. I. Temperatures of Metal-Poor Stars

abstract:
  Determining the properties of old stellar systems using evolutionary
population synthesis requires a library of reliable model stellar fluxes.
Empirical libraries are limited to spectra of stars in the solar neighborhood,
with nearly solar abundances and abundance ratios. We report here a first step
towards providing a flux library that includes nonsolar abundances, based on
calculations from first principles that are calibrated empirically. We have
started with main-sequence stars, whose light dominates the mid-ultraviolet
spectrum of an old stellar system. We have calculated mid-ultraviolet spectra
for the Sun and nine nearby, near-main-sequence stars spanning metallicities
from less than 1/100 solar to greater than solar, encompassing a range of
light-element abundance enhancements. We first determined temperatures of eight
of the stars by analyzing optical echelle spectra together with the
mid-ultraviolet. Both could be matched at the same time only when models with
no convective overshoot were adopted, and only when an approximate chromosphere
was incorporated near the surface of relatively metal-rich models. Extensive
modifications to mid-UV line parameters were also required, notably the manual
assignment of approximate identifications for mid-UV lines missing from
laboratory linelists. Without recourse to additional missing opacity, these
measures suffice to reproduce in detail almost the entire mid-UV spectrum of
solar-temperature stars up to one-tenth solar metallicity, and the region from
2900A to 3100A throughout the entire metallicity range. Ramifications for
abundance determinations in individual metal-poor stars and for age-metallicity
determinations of old stellar systems are briefly discussed, with emphasis on
the predictive power of the calculations.


title: Mode Generating Mechanism in Inflation with Cutoff

abstract:
  In most inflationary models, space-time inflated to the extent that modes of
cosmological size originated as modes of wavelengths at least several orders of
magnitude smaller than the Planck length. Recent studies confirmed that,
therefore, inflationary predictions for the cosmic microwave background
perturbations are generally sensitive to what is assumed about the Planck
scale. Here, we propose a framework for field theories on curved backgrounds
with a plausible type of ultraviolet cutoff. We find an explicit mechanism by
which during cosmic expansion new (comoving) modes are generated continuously.
Our results allow the numerical calculation of a prediction for the CMB
perturbation spectrum.


title:
Size-selective concentration of chondrules and other small particles in
  protoplanetary nebula turbulence

abstract:
  Size-selective concentration of particles in a weakly turbulent
protoplanetary nebula may be responsible for the initial collection of
chondrules and other constituents into primitive body precursors. This paper
presents the main elements of this process of turbulent concentration. In the
terrestrial planet region, both the characteristic size and size distribution
of chondrules are explained. "Fluffier" particles would be concentrated in
nebula regions which were at a lower gas density and/or more intensely
turbulent. The spatial distribution of concentrated particle density obeys
multifractal scaling}, suggesting a close tie to the turbulent cascade process.
This scaling behavior allows predictions of the probability distributions for
concentration in the protoplanetary nebula to be made. Large concentration
factors (>10^5) are readily obtained, implying that numerous zones of particle
density significantly exceeding the gas density could exist. If most of the
available solids were actually in chondrule sized particles, the ensuing
particle mass density would become so large that the feedback effects on gas
turbulence due to mass loading could no longer be neglected. This paper
describes the process, presenting its basic elements and some implications,
without including the effects of mass loading.


title:
Chandra High-Resolution Camera Observations of the Luminous X-Ray Source
  in the Starburst Galaxy M82

abstract:
  We have analyzed Chandra High Resolution Camera observations of the starburst
galaxy M82, concentrating on the most luminous x-ray source. We find a position
for the source of $\rm R.A. = 09^h 55^m 50^s.2, decl. = +69^{\circ} 40\arcmin
46\arcsec.7$ (J2000) with a $1\sigma$ radial error of $0.7\arcsec$. The
accurate x-ray position shows that the luminous source is not at the dynamical
centre of M82 nor coincident with any suggested radio AGN candidate. The source
is highly variable between observations, which suggests that the source is a
compact object and not a supernova or remnant. There is no significant short
term variability within the observations. Dynamical friction and the off-center
position place an upper bound of $10^{5} - 10^{6} M_{\odot}$ on the mass of the
object, depending on its age. The x-ray luminosity suggests a compact object
mass of at least $500 M_{\odot}$. Thus, the luminous source in M82 may
represent a new class of compact object with a mass intermediate between those
of stellar mass black hole candidates and supermassive black holes.


title:
Bondi-Hoyle-Lyttleton Accretion Model for Low-luminosity X-ray Sources
  in Globular Clusters

abstract:
  We present a new model for low-luminosity X-ray sources in globular clusters,
with L_x < 10^34 erg/s. The model we propose is that of a single neutron star
accreting from cluster gas that has accumulated as a natural product of stellar
evolution. An analytic luminosity function is derived under the assumption that
the speed distribution of neutron stars in the central region of a cluster is
described by a Maxwellian, and that the density and temperature of the gas are
uniform. Predictions of the model and implications for the gas content of
globular clusters are discussed.


title:
First Stellar Abundances in NGC 6822 from VLT-UVES and Keck-HIRES
  Spectroscopy

abstract:
  We have obtained the first high resolution spectra of individual stars in the
dwarf irregular galaxy, NGC 6822. The spectra of the two A-type supergiants
were obtained at the VLT and Keck Observatories, using UVES and HIRES,
respectively. A detailed model atmospheres analysis has been used to determine
their atmospheric parameters and elemental abundances. The mean iron abundance
from these two stars is $<$[Fe/H]$>=-$0.49 $\pm$0.22 ({\it $\pm$0.21}, with Cr
yielding a similar underabundance, $<$[Cr/H]$>=-$0.50 $\pm$0.20 ({\it
$\pm$0.16}). This confirms that NGC 6822 has a metallicity that is slightly
higher than that of the SMC, and is the first determination of the present-day
iron-group abundances in NGC 6822. The mean stellar oxygen abundance,
12+log(O/H)=8.36 $\pm$0.19 ({\it $\pm$0.21}),is in good agreement with the
nebular oxygen results. Oxygen has the same underabundance as iron,
$<$[O/Fe]$>$=+0.02 $\pm$0.20 ({\it $\pm$0.21}). This O/Fe ratio is very similar
to that seen in the Magellanic Clouds, which supports the picture that chemical
evolution occurs more slowly in these lower mass galaxies, although the O/Fe
ratio is also consistent with that observed in comparatively metal-poor stars
in the Galactic disk. Combining all of the available abundance observations for
NGC 6822 shows that there is no trend in abundance with galactocentric
distance. However, a subset of the highest quality data are consistent with a
radial abundance gradient.


title: Radio-Quiet Quasars in the Direction of the Northern Hubble Deep Field

abstract:
  We match quasars discovered in a multi-color survey centered on the northern
Hubble Deep Field (HDF) with radio sources from an ultra-deep radio survey.
Although 3 out of 12 quasars are detected at a level below 0.2 mJy at 1.4 GHz,
all of the quasars in the search area are radio-quiet by the criterion L_r <
10^{25} h^{-1}_{50} W/Hz. We combine this information with other radio surveys
of quasars so as to break the degeneracy between redshift and luminosity. In
the redshift range 0.02 < z < 3.64, the radio-loud fraction increases with
increasing optical luminosity, consistent with some degree of correlation
between the non-thermal optical and radio emissions. More tentatively, for low
luminosity quasars in the range -22.5 < M_B < -25, the radio-loud fraction
decreases with increasing redshift. We can infer from this that the radio
luminosity function evolves more slowly than the optical luminosity function.
The mechanism that leads to strong radio emission in only a small fraction of
quasars at any epoch is still unknown.


title: The Formation of the Milky Way Disk

abstract:
  We present theoretical results on the galactic abundance gradients of several
chemical species for the Milky Way disk, obtained using an improved version of
the two-infall model of Chiappini, Matteucci, & Gratton (1997) that
incorporates a more realistic model of the galactic halo and disk. This
improved model provides a satisfactory fit to the elemental abundance gradients
as inferred from the observations and also to other radial features of our
galaxy (i.e., gas, star formation rate and star density profiles). We discuss
the implications these results may have for theories of the formation of the
Milky Way and make some predictions that could in principle be tested by future
observations.


title:
Observations of the core of the Pleiades with the Chandra X-ray
  Observatory

abstract:
  We present results from a 36-ksec observation of the core of the Pleiades
open cluster using ACIS-I on the Chandra X-ray Observatory. We have detected 57
sources, most of which do not have previously known optical counterparts.
Follow-up photometry indicates that many of the detections are likely to be
AGNs, in accordance with extragalactic source counts, but some of the sources
may be previously undiscovered low-mass members of the Pleiades. We discuss our
dataset and our findings about X-ray emission from early-type stars as well as
very late type stars. In particular, the large X-ray fluxes, lack of
variability, and hardness ratios of the four Pleiades B6 IV -- F4 V stars
suggest a tentative conclusion that Pleiades stars in this spectral type range
are intrinsic X-ray sources rather than previously unknown binaries in which
the X-ray emission is from a late-type companion. Also the sensitivity of
Chandra allowed us to detect nonflare X-ray emission from late-M stars.


title: The Milky Way in Molecular Clouds: A New Complete CO Survey

abstract:
  New large-scale CO surveys of the first and second Galactic quadrants and the
nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2
m telescope, have been combined with 31 other surveys obtained over the past
two decades with that instrument and a similar telescope on Cerro Tololo in
Chile, to produce a new composite CO survey of the entire Milky Way. The survey
consists of 488,000 spectra that Nyquist or beamwidth (1/8-deg) sample the
entire Galactic plane over a strip 4-10 deg wide in latitude, and beamwidth or
1/4-deg sample nearly all large local clouds at higher latitudes.
  A map of molecular column density predicted from complete and unbiased
far-infrared and 21 cm surveys of the Galaxy was used both to determine the
completeness of the present survey and to extrapolate it to the entire sky at
|b| < 32 deg. The close agreement of the observed and predicted maps implies
that only ~2% of the total CO emission at |b| < 32 deg lies outside our current
sampling. Taking into account this small amount of unobserved emission, the
mean molecular column density decreases from ~3 E20 cm-2 at |b| = 5 deg to ~0.1
E20 cm-2 at |b| = 30 deg.
  The ratio of the predicted molecular column density map to the observed CO
intensity map provides a calibration of the CO-to-H2 mass conversion factor X =
N(H2)/Wco. Out of the Galactic plane (|b| > 5 deg), X shows little systematic
variation with latitude from a mean value of 1.8 +/- 0.3 E20 cm-2 K-1 km-1 s.
Given the large sky area and large quantity of CO data analyzed, we conclude
that this is the most reliable measurement to date of the mean X value in the
solar neighborhood.


title: The near-infrared view of SBS 0335-052

abstract:
  We present near-infrared (NIR) spectra, deep J, H and K low-resolution ima
ges, and high-resolution images in J and Ks of the low-metallicity blue dwarf
gal axy SBS 0335-052. These new NIR data, together with optical and
mid-infrared data from the literature, are used to constrain the properties and
the star formation history of the galaxy. The NIR spectral characteristics and
broadband colors of this galaxy are those of an extremely young starburst. We
find that the NIR emission is dominated by star formation occuring in clusters
younger than 5 Myr; no optically hidden star formation is revealed in our data.
We also find that a warm-dust component is necessary to explain the H-K color,
and is consistent with the mid-infrared spectral energy distribution. Finally,
we quantify the possible contribution from an evolved stellar populatio n.


title: On the Spectroscopic Diversity of Type Ia Supernovae

abstract:
  A comparison of the ratio of the depths of two absorption features in the
spectra of TypeIa supernovae (SNe Ia) near the time of maximum brightness with
the blueshift of the deep red Si II absorption feature 10 days after maximum
shows that the spectroscopic diversity of SNe Ia is multi-dimensional. There is
a substantial range of blueshifts at a given value of the depth ratio. We also
find that the spectra of a sample of SNe Ia obtained a week before maximum
brightness can be arranged in a ``blueshift sequence'' that mimics the time
evolution of the pre-maximum-light spectra of an individual SN Ia, the well
observed SN 1994D. Within the context of current SN Ia explosion models, we
suggest that some of the SNe Ia in our sample were delayed-detonations while
others were plain deflagrations.


title: Models for Multiband IR Surveys

abstract:
  Empirical 'backward' galaxy evolution models for IR-bright galaxies are
constrained using multiband IR surveys. A new Monte-Carlo algorithm is
developed for this task. It exploits a large library of realistic Spectral
Energy Distributions (SEDs) of 837 local IR galaxies (IRAS 25$\mu m$ selected)
from the UV (1000{\AA}) to the radio (20cm), including ISO-measured 3--13$\mu
m$ unidentified broad features (UIBs). The basic assumption is that the local
correlation between SEDs and Mid-Infrared (MIR) luminosities can be applied to
earlier epochs of the Universe. Three populations of IR sources are considered
in the evolution models. These include (1) starburst galaxies, (2) normal
late-type galaxies, and (3) galaxies with AGN. A set of models so constructed
are compared with data from the literature. Predictions for number counts,
confusion limits, redshift distributions, and color-color diagrams are made for
multiband surveys using the upcoming SIRTF satellite.


title:
The Starburst-Interstellar Medium Interaction of NGC 1569 I. Location
  and Nature of He II Sources Using Hubble Space Telescope WFPC2 Imagery

abstract:
  We present the detection of He II sources in the Im galaxy NGC 1569 from HST
WFPC2 imagery. Out of the fifteen detections, seven were Wolf-Rayet stars, five
were stellar clusters with associated He II emission, and three were sources of
unknown origin. The detected Wolf-Rayet stars' colors and magnitudes are
similar to Large Magellanic Cloud late-type WN stars. The physical origin of
the other He II sources are discussed. We conclude that the equivalent of
51+/-19 WNL stars have been detected in NGC 1569, and we have estimated the
total Wolf-Rayet population in NGC 1569 as 78+/-51. These numbers are compared
with the Wolf-Rayet stellar populations in the SMC, LMC, Milky Way, and other
starburst galaxies relative to their luminosities, dynamical masses, and
ionized gas masses. Previous to this study, Wolf-Rayet stars in NGC 1569 were
not detected using ground-based imagery, but were only indicated through
longslit spectroscopy. This is the first time the exact locations of the
Wolf-Rayet stars in this nearby, well-studied, "post-starburst" galaxy have
been determined.


title:
Polarization Signal of Distant Clusters and Reconstruction of Primordial
  Potential Fluctuations

abstract:
  We examine the polarization signal of the cosmic microwave background
radiation associated with distant clusters.
  The polarization is induced by the Thomson scattering of microwave photons
with ionized gas of clusters and contains information of quadrupole temperature
anisotropies observed at the clusters. The three-dimensional map of the signal
are expressed in terms of the spin-weighted harmonics for its angular
dependence. Its radial dependence is expanded perturbatively with respect to
the distances (equivalently redshifts) to the clusters.
  The independent information that we can extract out from the map is clarified
explicitly.


title: An HI Survey of the Great Attractor Region

abstract:
  A blind HI survey using the Parkes telescope at |b|<5 deg, 300 deg < l < 332
deg has so far revealed 305 galaxies, most of which were previously unknown.
These galaxies are used to map out the distribution of filaments and voids out
to 10000 km/s. A preliminary measurement of the galaxy overdensity suggests
only a moderate overdensity is present, and that the excess mass (above the
background density) is ~2.10^{15}.Omega.M(sun). This is below the mass
predicted in POTENT reconstructions of the local velocity field, and implies
that the `Great Attractor' (GA) is not as massive as these reconstructions
indicate, or does not lie hidden in the region investigated.


title:
Search for Millisecond Periodicities in Type I X-ray Bursts of the Rapid
  Burster

abstract:
  We have searched the rising portion of type I X-ray bursts observed from the
Rapid Burster with the Rossi X-ray Timing Explorer for the presence of
periodicities. The 95 per cent confidence upper limit on the average
root-mean-square variation of near coherent pulsations with a width of <1 Hz
(in 60--2048 Hz) during the first second of the bursts is <8.8 per cent. We
find a possible detection (>98 per cent significance) at 306.5 Hz.


title:
Log N -- Log S distributions of accreting and cooling isolated neutron
  stars

abstract:
  We model populations of isolated neutron stars in the Galaxy following their
orbital and magneto-rotational evolution. It is shown that accretors become
more abundant than coolers at fluxes below $\sim 10^{-13}$ erg cm$^{-2}$
s$^{-1},$ and one can predict that about one accreting neutron star per square
degree should be observed at the {\it Chandra} and {\it Newton} flux limits of
$\sim 10^{-16}$ erg cm$^{-2}$ s$^{-1}.$ The soft ROSAT sources associated with
isolated neutron stars can be relatively young cooling objects only if the
neutron star birth rate in the Solar vicinity during the last $\sim 10^6$ yr is
higher than that inferred from radiopulsar observations.


title: The Chemical Evolution of the Universe I: High Column Density Absorbers

abstract:
  We construct a simple, robust model of the chemical evolution of galaxies
from high to low redshift, and apply it to published observations of damped
Lyman-alpha quasar absorption line systems (DLAs). The elementary model assumes
quiescent star formation and isolated galaxies (no interactions, mergers or gas
flows). We consider the influence of dust and chemical gradients in the
galaxies, and hence explore the selection effects in quasar surveys. We fit
individual DLA systems to predict some observable properties of the absorbing
galaxies, and also indicate the expected redshift behaviour of chemical element
ratios involving nucleosynthetic time delays.
  Despite its simplicity, our `monolithic collapse' model gives a good account
of the distribution and evolution of the metallicity and column density of
DLAs, and of the evolution of the global star formation rate and gas density
below redshifts z 3. However, from the comparison of DLA observations with our
model, it is clear that star formation rates at higher redshifts (z>3) are
enhanced. Galaxy interactions and mergers, and gas flows very probably play a
major role.


title:
Gravitational Collapse in Turbulent Molecular Clouds. II.
  Magnetohydrodynamical Turbulence

abstract:
  Hydrodynamic supersonic turbulence can only prevent local gravitational
collapse if the turbulence is driven on scales smaller than the local Jeans
lengths in the densest regions, a very severe requirement (Paper I). Magnetic
fields have been suggested to support molecular clouds either magnetostatically
or via magnetohydrodynamic (MHD) waves. Whereas the first mechanism would form
sheet-like clouds, the second mechanism not only could exert a pressure onto
the gas counteracting the gravitational forces, but could lead to a transfer of
turbulent kinetic energy down to smaller spatial scales via MHD wave
interactions. This turbulent magnetic cascade might provide sufficient energy
at small scales to halt local collapse.
  We test this hypothesis with MHD simulations at resolutions up to 256^3
zones, done with ZEUS-3D. We first derive a resolution criterion for
self-gravitating, magnetized gas: in order to prevent collapse of
magnetostatically supported regions due to numerical diffusion, the minimum
Jeans length must be resolved by four zones. Resolution of MHD waves increases
this requirement to roughly six zones. We then find that magnetic fields cannot
prevent local collapse unless they provide magnetostatic support. Weaker
magnetic fields do somewhat delay collapse and cause it to occur more uniformly
across the supported region in comparison to the hydrodynamical case. However,
they still cannot prevent local collapse for much longer than a global
free-fall time.


title: Ultra-high angular resolution by gravitational microlensing

abstract:
  The problem of restoration of the source brightness distribution from an
analysis of the stellar and AGNs microlensing light curves is investigated. In
case of microlensing of stars by a point-mass lens as well as for caustic
crossing events for binary lens the problem can be reduced to solution of the
Fredholm integral equation of the 1st kind. Concrete form of the kernel of this
equation depends on a type of the microlensing event. Assuming the circular
symmetry of the stellar disk the search for radial brightness distribution can
be carried out in the special compact sets of functions which correspond to the
physics of the problem. These sets include the non-negative functions that are
not increasing with increasing distance from the center of stellar disk and the
upwards convex non-negative functions. The brightness distribution for the AGNs
accretion disks is also circularly symmetric, but only in the locally co-moving
frame. Therefore, the kernel of integral equation that determined the AGN
microlensing light curve must take into account equally with the projection
effect on picture plane the influence of relativistic effects. The search for
solution of this equation can be carried out in the set of non-negative down
convex functions. The results of analysis of microlensing light curves for the
red giant MACHO Alert 95-30 and the A6 star MACHO 98-SMC-1 as well as the
results of numerical simulations for the AGN microlensing observations are
given.


title:
Superclustering of Faint Galaxies in the Field of a QSO Concentration at
  z~1.1

abstract:
  We report on a wide-area (48' x 9') imaging survey of faint galaxies in R and
I bands toward the 1338+27 field where an unusual concentration of five QSOs at
z\sim1.1, embedded in a larger-scale clustering of 23 QSOs, is known to exist.
Using a quite homogeneous galaxy catalog with a detection completeness limit of
I~23.5, we detect a significant clustering signature of faint red galaxies with
I > 21 and R-I > 1.2 over a scale extending to ~20h^{-1}_{50} Mpc. Close
examination of the color-magnitude diagram, the luminosity function, and the
angular correlation function indeed suggests that those galaxies are located at
z~1.1 and trace the underlying large-scale structure at that epoch, together
with the group of 5 QSOs. Since the whole extent of the cluster of 23 QSOs
(~70h^{-1}_{50} Mpc) is roughly similar to the local ``Great Wall'', the area
may contain a high-redshift counterpart of superclusters in the local universe.


title: Do clusters contain a large population of dwarf galaxies?

abstract:
  We analyze systematic effects in the determination of the galaxy luminosity
function in clusters using a deep mock catalogue constructed from a numerical
simulation of a hierarchical universe. The results indicate a strong tendency
to derive a rising faint end ($\alpha \lsim -1.5$) in clusters selected in two
dimensions, using a galaxy catalogue constructed with a universal flat
luminosity function with $\alpha \simeq -1.0$. This is due to the projection
effects inherent in catalogues of clusters constructed using 2 dimensional
data. Many of the clusters found in 2d have no significant 3d counterparts, and
most suffer from massive background contamination that cannot be corrected for
by subtracting random offset fields. The luminosity function of high surface
brightness galaxies in the field and within small groups follows a Schechter
function with a fairly flat faint end slope, $n(L)\propto L^{\alpha}$ with
$\alpha = -0.9$ to -1.2. On the contrary, observational studies of clusters
constructed using Abell, EDCC and APM catalogues are systematically found to
have steeper luminosity functions with $\alpha = -1.4$ to -2.0. This may be
attributed to projection effects rather than a dominant population of high
surface brightness dwarf galaxies ($M\gsim M^*+2$) in clusters. It should be
straighforward to confirm our results by measuring redshifts of these faint
cluster galaxies.


title:
Broad-band X-ray spectra of the persistent black hole candidates LMC X-1
  and LMC X-3

abstract:
  We report on observations of the two persistent black hole candidates LMC X-3
and LMCX-1 performed with \BS in October 1997. The flux of LMC X-1 was possibly
measured up to 60 keV, but there is a possible confusion with PSR 0540-69. Fits
with an absorbed multicolor disk black body are not satisfactory, while the
superposition of this model with a power law is acceptable. The sources showed
little variations during the observations. However in LMC X-1 some X-ray color
dependence on intensity is apparent, indicating a hardening of the spectrum in
the second half of the observation. The inner disk radius and temperature
change, featuring the same (anti)correlation found in {\it RXTE} data (Wilms et
al. 2000). QPOs were searched for. In LMC X-3 none was detected; in LMCX-1 a 3
sigma upper (9% rms) limit is given at 0.07 Hz, the frequency of the QPO
discovered with Ginga.


title:
{Chemo-spectrophotometric evolution of spiral galaxies: IV. Star
  formation efficiency and effective ages of spirals

abstract:
  We study the star formation history of normal spirals by using a large and
homogeneous data sample of local galaxies. For our analysis we utilise detailed
models of chemical and spectrophotometric galactic evolution, calibrated on the
Milky Way disc. We find that star formation efficiency is independent of
galactic mass, while massive discs have, on average, lower gas fractions and
are redder than their low mass counterparts; put together, these findings
convincingly suggest that massive spirals are older than low mass ones. We
evaluate the effective ages of the galaxies of our sample and we find that
massive spirals must be several Gyr older than low mass ones. We also show that
these galaxies (having rotational velocities in the 80-400 km/s range) cannot
have suffered extensive mass losses, i.e. they cannot have lost during their
lifetime an amount of mass much larger than their current content of gas+stars.


title: Magnetohydrodynamical Non-radiative Accretion Flows in Two-Dimensions

abstract:
  We present the results of axisymmetric, time-dependent magnetohydrodynamic
simulations of accretion flows around black holes. The calculations begin from
a rotationally supported thick torus which contains a weak poloidal field.
Accretion is produced by growth and saturation of the magnetorotational
instability (MRI) provided the wavelength of the fastest growing mode is less
than the thickness of the torus. Using a computational grid that spans more
than two decades in radius, we compare the time-averaged properties of the flow
to previous hydrodynamical simulations. The net mass accretion rate is small
compared to the mass inflow and outflow rates at large radii associated with
turbulent eddies. Turbulence is driven by the MRI rather than convection. The
two-dimensional structure of the time-averaged flow is significantly different
compared to the hydrodynamical case. We discuss the limitations imposed on our
results by the assumption of axisymmetry and the relatively small radial
domain.


title:
A Broad Search for Counterrotating Gas and Stars: Evidence for Mergers
  and Accretion

abstract:
  We measure the frequency of bulk gas-stellar counterrotation in a sample of
67 galaxies drawn from the Nearby Field Galaxy Survey, a broadly representative
survey of the local galaxy population down to M_B-15. We detect 4
counterrotators among 17 E/S0's with extended gas emission (24% +8 -6). In
contrast, we find no clear examples of bulk counterrotation among 38 Sa-Sbc
spirals, although one Sa does show peculiar gas kinematics. This result implies
that, at 95% confidence, no more than 8% of Sa-Sbc spirals are bulk
counterrotators. Among types Sc and later, we identify only one possible
counterrotator, a Magellanic irregular. We use these results together with the
physical properties of the counterrotators to constrain possible origins for
this phenomenon.


title: Kinematic Asymmetries in a Broad Galaxy Sample

abstract:
  We analyze asymmetries in the gas rotation curves of 113 galaxies drawn from
the Nearby Field Galaxy Survey, spanning a broad range of luminosities and
morphologies. If the origin of the rotation curve is chosen to minimize the
asymmetry, then ~23% of sample galaxies show asymmetry >5% within 1.3r_e.
However, not all gas kinematic asymmetries indicate asymmetries in the
underlying potential.


title: Frequency of Gas-Stellar Counterrotation

abstract:
  We search for bulk counterrotation of the gas and stars in 67 galaxies of all
types and a wide range of luminosities. Bulk counterrotation characterizes
\~25-30% of E/S0's with extended gas, but at most a few percent of Sa-Sbc
spirals. For S0's, the frequency of counterrotation we derive agrees with
previous work, but we sample significantly fainter luminosities. Thus the
agreement suggests that similar formation mechanisms may operate over a wide
range of physical scales.


title:
Iron Abundance Profiles of 12 Clusters of Galaxies Observed With
  BeppoSAX

abstract:
  We have derived azimuthally-averaged radial iron abundance profiles of the
X-ray gas contained within 12 clusters of galaxies with redshift 0.03 < z < 0.2
observed with BeppoSAX. We find evidence for a negative metal abundance
gradient in most of the clusters, particularly significant in clusters that
possess cooling flows. The composite profile from the 12 clusters resembles
that of cluster simulations of Metzler & Evrard (1997). This abundance gradient
could be the result of the spatial distribution of gas-losing galaxies within
the cluster being more centrally condensed than the primordial hot gas. Both
inside and outside the core region, we find a higher abundance in cooling flow
clusters than in non-cooling flow clusters. Outside of the cooling region this
difference cannot be the result of more efficient sputtering of metals into the
gaseous phase in cooling flow clusters, but might be the result of the mixing
of low metallicity gas from the outer regions of the cluster during a merger.


title: A Critical Examination of Hypernova Remnant Candidates in M101. I. MF83

abstract:
  The SNR candidate MF83 in M101 is coincident with a very luminous X-ray
source. Based on the high X-ray luminosity, it has been suggested that MF83 is
a "hypernova remnant" requiring an explosion energy about two orders of
magnitude higher than normal supernovae. We have analyzed high-quality
ground-based and HST observations of MF83, and find that MF83 is a star
formation region, consisting of a large ionized gas shell and four HII regions
along its periphery. Continuum images show OB associations in these HII regions
and within the large shell. The shell has an expansion velocity of $\sim$50
km/s and a diameter of $\sim$270 pc. The optical properties of this shell in
MF83 are similar to those of X-ray-bright superbubbles in the Large Magellanic
Cloud. If the X-ray emission is indeed diffuse, the implied thermal energy in
MF83 is high, a few $\times10^{52}$ ergs. This amount of thermal energy
requires a large number of concentrated supernova explosions or one powerful
explosion. Future X-ray observations with a high angular resolution are needed
to resolve the diffuse emission and point sources in MF83, in order to
determine more accurately the thermal energy in the shell interior and its
required explosion energy.


title:
Electric Charge and Magnetic Flux on Rotating Black Holes in a
  Force-Free Magnetosphere

abstract:
  The electric charge on rotating black holes is calculated to be ~ BJ in the
force-free configuration of Ghosh (2000), with a horizon flux of ~ BM^2. This
charge is gravitationally weak for B ~ 10^{15} G, so that the Kerr metric
applies. Being similar to the electric charge of a magnetar, both electric
charge and magnetic flux should be, in sign and order of magnitude, continuous
during stellar collapse into a black hole. Extraction of the rotational energy
from newly formed black holes may proceed by interaction with the magnetic
field. Keywords:black hole physics --magnetic fields


title:
Profiles of thermal line emission from advection dominated accretion
  flows

abstract:
  Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than $15^{\circ}$, where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.


title:
The relation between extended radio and line emission for radio-loud
  quasars

abstract:
  We explore the relationship between the extended radio and line emission for
a radio-loud quasar sample including both core-dominated and lobe-dominated
quasars. A strong correlation is present between the extended radio and
broad-line emission. The core emission is also correlated with the broad-line
emission for core-dominated quasars in the sample. The statistic behaviour on
the core emission of lobe-dominated quasars is rather different from that of
core-dominated quasars. The extended radio luminosity is a good tracer for jet
power, while the core luminosity can only be a jet power tracer for
core-dominated quasars.


title: Results from the AMANDA High Energy Neutrino Detector

abstract:
  This paper briefly summarizes the search for astronomical sources of
high-energy neutrinos using the AMANDA-B10 detector. The complete data set from
1997 was analyzed. For E_mu>10 TeV, the detector exceeds 10,000 m^2 in
effective area between declinations of 25 and 90 degrees. Neutrinos generated
in the atmosphere by cosmic ray interactions were used to verify the overall
sensitivity of the detector. The absolute pointing accuracy and angular
resolution has been confirmed by the analysis of coincident events between the
SPASE air shower array and the AMANDA detector. Preliminary flux limits from
point source candidates are presented. For declinations larger than +45
degrees, our results compare favorably to existing limits for sources in the
Southern sky. We also present the current status of the searches for high
energy neutrino emission from diffusely distributed sources, GRBs, and WIMPs
from the center of the earth.


title: The Polarization Variability in the Optical Afterglow of GRB 990712

abstract:
  In a recent paper, Rol and colleagues present evidence for a variable
polarization in the optical afterglow following the gamma-ray burst GRB 990712.
The variation is highly significant, but the position angle appears time
independent. Contrary to their conclusion, we point out that this can in fact
be explained with existing afterglow models, namely that of a laterally
expanding jet.


title:
Evolutionary Self-Energy-Loss Effects in Compact Binary Systems:
  Importance of Rapid Rotation and of Equation of State

abstract:
  The spin-down of a millisecond pulsar in a compact binary system leads to
self-energy losses, that cause the binary's orbital period to increase (the
effect being of first post-Newtonian (1PN) order). If the pulsar's
period-derivative is not exceedingly small, this effect can become measurable
in long-term high-precision timing measurements of the binary's orbital motion.
We use rotating compressible spheroids to obtain an approximate, explicit
expression for the orbital period derivative, due to spin-down, valid to 1PN
order. This expression can be used to observationally constrain the pulsar's
moment of inertia, and, combined with other observations, the high-density
equation of state of compact stars. We apply our expression to representative
models of millisecond pulsars in binary systems and demonstrate the importance
of including higher-order rotational effects as well as the importance of the
choice of equation of state, which both have been neglected, so far, in the
literature. The computed increase in orbital period is larger, by as much as
32%, when the higher-order rotational effects are included, while it can change
by more than a factor of two between different plausible equations of state.


title:
On the presence of Silicon and Carbon in the pre-maximum spectrum of the
  Type Ia SN 1990N

abstract:
  The spectrum of the normal Type Ia SN 1990N observed very early on (14 days
before B maximum) was analysed by Fisher et al (1997), who showed that the
large width and the unusual profile of the strong line near 6000\AA can be
reproduced if the line is assumed to be due to \CII 6578, 6583\AA and if Carbon
is located in a high velocity shell. This line is one of the characterising
features of SNe Ia, and is usually thought to be due to \SiII. A Monte Carlo
spectrum synthesis code was used to investigate this suggestion further. The
result is that if a standard explosion model is used the mass enclosed in the
shell at the required high velocity (25,000--35,000 \kms) is too small to give
rise to a strong \CII line. At the same time, removing Silicon has a negative
effect on the synthetic spectrum at other wavelengths, and removing Carbon from
the lower velocity regions near the photosphere makes it difficult to reproduce
two weak lines which are naturally explained as \CII, one of them being the
line which Fisher et al (1997) suggested is responsible for the strong 6000\AA
feature. However, synthetic spectra confirm that although \SiII can reproduce
most of the observed 6000\AA line, the red wing of the line extends too far to
be compatible with a \SiII origin, and that the flat bottom of the line is also
not easy to reproduce. The best fit is obtained for a normal SN Ia abundance
mix at velocities near the photosphere (15,500-19,000 \kms) and an outer
Carbon-Silicon shell beyond 20,000 \kms. This suggests that mixing is not
complete in the outer ejecta of a SN Ia. Observations at even earlier epochs
might reveal to what extent a Carbon shell is unmixed.


title:
Huddled Masses Yearning to Stream Free: Globular Clusters in the Hearts
  of Galaxy Clusters

abstract:
  Extremely rich populations of globular clusters, numbering ten thousand or
more, surround the central giant galaxies in rich clusters. I discuss some
recent spectroscopic and photometric observations of these rich globular
clusters populations. In very nearby galaxy clusters, the globular cluster
velocities can be used to trace the transition from the galaxy potential to the
larger cluster potential. Beyond cz \approx 3000 km/s, the globulars are too
faint for spectroscopic studies with even the largest telescopes and cease to
be useful dynamical tracers. However, the spatial distribution and size of the
globular population also contains information on the central mass distribution
of the cluster and can be measured out to cz > 20,000 km/s. Overall, the data
suggest that these rich globular cluster populations are comprised of normal,
old globulars, the majority of which were assembled in the cluster centers
before most of the stars in the cD galaxy were formed.


title: Simulating clusters of galaxies: a brief history of `N' and overmerging

abstract:
  I review four decades of numerical simulations of galaxy clusters focussing
on the attempts to resolve their internal structure. Overmerging describes the
numerical or physical disruption of dark matter halos within dense
environments. This problem was inherent in simulations prior to 1998 but can be
completely overcome with current algorithms and hardware. We can now resolve
many thousands of subhalos within clusters and we may have converged on their
inner structure, allowing several new tests of the hierarchical structure
formation model and the nature of dark matter.


title: Dynamical effects on galaxies in clusters

abstract:
  The observed morphological evolution since z ~ 0.5 within galaxy clusters
provides evidence for a hierarchical universe. This evolution is driven by
dynamical effects that operate within the cluster environment -- suppression of
star-formation by ram-pressure and viscous stripping of the intra-galactic
medium and tidal heating of disks by gravitational encounters.


title: Evidence for Massive Black Holes in Nearby Galactic Nuclei

abstract:
  Masses of black holes in nearby galactic nuclei can be measured in a variety
of ways, using stellar and gaseous kinematics. Reliable black hole masses are
known for several dozen objects, so that demographic questions can start to be
addressed with some confidence. Prospects for the near future are discussed
briefly.


title:
Discovery of a Luminous, Variable, Off-Center Source in the Nucleus of
  M82 with the Chandra HRC

abstract:
  We present results from observations of the most famous starburst galaxy M82
with the High-Resolution Camera onboard the Chandra X-Ray Observatory. We found
nine sources in the central 1' x 1' region, but no source was detected at the
galactic center. Comparing the observations on 1999 October 28 and on 2000
January 20, we found four of the nine sources showed significant time
variability. In particular, CXOM82J095550.2+694047, which is 9" away from the
galactic center, showed extremely large time variability. We conclude that this
source is the origin of the hard X-ray time variability of M82 detected with
ASCA. Assuming a spectral shape obtained by the ASCA observation, its
luminosity in the 0.5 -- 10 keV band changed from 1.2E40 erg/s on 1999 October
28 to 8.7E40 erg/s on 2000 January 20.


title:
Optical follow-up of the REFLEX survey: a new perspective in cluster
  studies

abstract:
  After the completion of the catalogue built with ESO key program (REFLEX), we
are beginning to explore the multiband optical characteristics of a subsample
of those clusters selected in a statistically independent way. We have already
observed in B, V, R, 9 of the about 50 clusters of the subsample, with 0.15 \le
z \le 0.18. More time has been allocated by ESO for our project in March 2001.
We will therefore be able to compare X-ray and optical morphologies and
luminosities and, thanks to the large field of view of the WFI instrument,
assess the luminosity function and the color segregation in the cluster on a
robust statistical basis. In this poster we present the project, the technical
problems we are facing in the reduction phase, and show the first preliminary
results, which seem very encouraging.


title: Rotation and H-alpha Emission Above and Below the Substellar Boundary

abstract:
  I present the results of a multiyear survey of very low mass stars and brown
dwarfs, at high spectral resolution. The spectra were gathered with the HIRES
echelle at the Keck Observatory. Some of these objects are stellar and others
are substellar (or ambiguous). Early indications that such objects can be
rapidly rotating but display little H-alpha emission turn out to be commonly
true. This is the opposite of the relation between rotation and activity in
solar-type stars. The H-alpha surface flux drops precipitously at the bottom of
the main sequence, and seems to be related to the luminosity or temperature of
the objects. There is a general trend to higher rotation velocities as one
looks at objects of lower luminosity. I discuss several possible explanations
for these results. The dynamos for these objects are probably fully turbulent,
driven by convection, and thus more directly related to the object's
luminosity. They may be quenched when the rotational velocities become too fast
in comparison to the convective velocities
  (supersaturation). Another possibility is that the atmospheres of the cooler
objects are becoming sufficiently neutral to decouple atmospheric motions from
the field. Either of these could explain why young brown dwarfs can be
magnetically active while older brown dwarfs are not. A final possibility is
that instead of being quenched, the field configuration in rapid rotators
changes to a less conducive form for dissipative heating. This could explain
why flares are occasionally seen on generally inactive objects.


title: Black Holes in Centers of Disk Galaxies - Spectroscopy with a Wide Slit

abstract:
  Motivated by STIS observations of more than 50 nearby galactic nuclei, we
consider long-slit emission-line spectra when the slit is wider than the
instrumental PSF. The finite width of the slit generates complex patterns in
the spectra that can have considerable diagnostic power if they are modeled
with adequate sophistication. They allowed us to develop a new method for
estimating the BH mass that gives fuller information and higher sensitivity to
BH detection than traditional methods.


title:
First Structure Formation: A Simulation of Small Scale Structure at High
  Redshift

abstract:
  We describe the results of a simulation of collisionless cold dark matter in
a LambdaCDM universe to examine the properties of objects collapsing at high
redshift (z=10). We analyze the halos that form at these early times in this
simulation and find that the results are similar to those of simulations of
large scale structure formation at low redshift. In particular, we consider
halo properties such as the mass function, density profile, halo shape, spin
parameter, and angular momentum alignment with the minor axis. By understanding
the properties of small scale structure formation at high redshift, we can
better understand the nature of the first structures in the universe, such as
Population III stars.


title: Resonant capture by inward migrating planets

abstract:
  We investigate resonant capture of small bodies by planets that migrate
inwards, using analytic arguments and three-body integrations. If the orbits of
the planet and the small body are initially circular and coplanar, the small
body is captured when it crosses the 2:1 resonance with the planet. As the
orbit shrinks it becomes more eccentric, until by the time its semimajor axis
has shrunk by a factor of four, its eccentricity reaches nearly unity
(1-e<<10^{-4}). In typical planetary systems, bodies in this high-eccentricity
phase are likely to be consumed by the central star. If they can avoid this
fate, as migration continues the inclination flips from 0 to i=180 degrees;
thereafter the eccentricity declines until the semimajor axis is a factor of
nine smaller than at capture, at which point the small body is released from
the 2:1 resonance on a nearly circular retrograde orbit. Small bodies captured
into resonance from initially inclined or eccentric orbits can also be ejected
from the system, or released from the resonance on highly eccentric polar
orbits (i\simeq 90 degrees) that are stabilized by a secular resonance. We
conclude that migration can drive much of the inner planetesimal disk into the
star, and that post-migration multi-planet systems may not be coplanar.


title:
Supernova data may be unable to distinguish between quintessence and
  k-essence

abstract:
  We consider the efficacy of using luminosity distance measurements of deep
redshift supernovae to discriminate between two forms of dark energy,
quintessence (a scalar field with canonical kinetic terms rolling down a
potential) and k-essence (a scalar field whose cosmic evolution is driven
entirely by non-linear kinetic terms). The primary phenomenological distinction
between the two types of models that can be quantified by supernova searches
(at least in principle) is that the equation of state $w\equiv p/\rho$ of
quintessence is falling today while that of k-essence is rising. By simulating
$10^5$ possible datasets that SNAP could obtain, we show that even if the mass
density $\Omega_m$ is known exactly, an ambiguity remains that may not allow a
definitive distinction to be made between the two types of theories.


title: The X-Ray Photoionized Wind in Cen X-3/V779 Cen

abstract:
  We analyze the ASCA spectrum of the Cen X-3 X-ray binary system in eclipse
using atomic models appropriate to recombination-dominated level population
kinetics in an overionized plasma. In order to estimate the wind
characteristics, we first fit the eclipse spectrum to a single-zone
photoionized plasma model. We then fit spectra from a range of orbital phases
using global models of photoionized winds from the companion star and the
accretion disk that account for the continuous distribution of density and
ionization state. We find that the spectrum can be reproduced by a density
distribution of the form derived by Castor, Abbot, & Klein (1975) for
radiation-driven winds with with the value of the mass-loss rate divided by the
terminal velocity consistent with values for isolated stars of the same stellar
type. This is surprising because the neutron star is very luminous (~10^38
erg/s) and the X-rays from the neutron star should ionize the wind and destroy
the ions that provide the opacity for the radiation-driven wind. Using the same
functional form for the density profile, we also fit the spectrum to a
spherically symmetric wind centered on the neutron star, a configuration chosen
to represent a disk wind. We argue that the relatively modest orbital variation
of the discrete spectrum rules out a disk wind hypothesis.


title:
A Complete Survey of Case A Binary Evolution with Comparison to Observed
  Algol-Type Systems

abstract:
  We undertake a comparison of observed Algol-type binaries with a library of
computed Case A binary evolution tracks. The library consists of 5500 binary
tracks with various values of initial primary mass M_{10}, mass ratio q_0, and
period P_0, designed to sample the phase-space of Case A binaries in the range
-0.10 < log M_{10} < 1.7. Each binary is evolved using a standard code with the
assumption that both total mass and orbital angular momentum are conserved.
This code follows the evolution of both stars until the point where contact or
reverse mass transfer occurs. The resulting binary tracks show a rich variety
of behavior which we sort into several subclasses of Case A and Case B. We
present the results of this classification, the final mass ratio and the
fraction of time spent in Roche Lobe overflow for each binary system. The
conservative assumption under which we created this library is expected to hold
for a broad range of binaries, where both components have spectra in the range
G0 to B1 and luminosity class III - V. We gather a list of relatively
well-determined observed hot Algol-type binaries meeting this criterion, as
well as a list of cooler Algol-type binaries where we expect significant
dynamo-driven mass loss and angular momentum loss. We fit each observed binary
to our library of tracks using a chi^2-minimizing procedure. We find that the
hot Algols display overall acceptable chi^2, confirming the conservative
assumption, while the cool Algols show much less acceptable chi^2 suggesting
the need for more free parameters, such as mass and angular momentum loss.


title: How the sun shines

abstract:
  This historical essay describes the struggle to understand how the sun
shines. The story begins with the disagreement between Kelvin and Darwin over
the age of the sun in the middle of the 19th century and continues through the
revelations of solar neutrino experiments at the conclusion of the 20th
century.

categories: astro-ph hep-ex hep-ph nucl-th physics.hist-ph physics.pop-ph


title:
Starburst or Seyfert? Adding a radio and far-infrared perspective to the
  investigation of activity in composite galaxies

abstract:
  It was once common to regard Seyfert and starburst galaxies as completely
different types of object, but there is growing recognition that these
classifications refer to the extremes of a continuous spectrum of galaxy types.
In a previous study we investigated a sample of galaxies with ambiguous optical
emission-line ratios and concluded from near-infrared spectroscopic
observations that the sample consisted of composite galaxies, containing both a
starburst and an active galactic nucleus (AGN). We now extend our study using
radio synthesis and long-baseline interferometer observations made with the
Australia Telescope, together with far-infrared IRAS observations, to discuss
the relative contribution of starburst and AGN components to the overall
luminosity of the composite galaxies. We find that only a small fraction of the
radio emission (<10%) can be attributed to an AGN, and that the majority of the
far-infrared emission (>90%) is probably due to the starburst component. We
also show that an AGN contribution to the optical emission of as little as 10%
is sufficient to account for the ambiguous line-ratio diagnostics.


title:
Equation of state of fully ionized electron-ion plasmas. II. Extension
  to relativistic densities and to the solid phase

abstract:
  The analytic equation of state of nonideal Coulomb plasmas consisting of
pointlike ions immersed in a polarizable electron background (physics/9807042)
is improved, and its applicability range is considerably extended. First, the
fit of the electron screening contribution in the free energy of the Coulomb
liquid is refined at high densities where the electrons are relativistic.
Second, we calculate the screening contribution for the Coulomb solid (bcc and
fcc) and derive an analytic fitting expression. Third, we propose a simple
approximation to the internal and free energy of the liquid one-component
plasma of ions, accurate within the numerical errors of the most recent Monte
Carlo simulations. We obtain an updated value of the coupling parameter at the
solid-liquid phase transition for the one-component plasma: Gamma_m = 175.0
(+/- 0.4).


title:
On the Timescale for the Formation of Protostellar Cores in Magnetic
  Interstellar Clouds

abstract:
  We revisit the problem of the formation of dense protostellar cores due to
ambipolar diffusion within magnetically supported molecular clouds, and derive
an analytical expression for the core formation timescale. The resulting
expression is similar to the canonical expression = t_{ff}^2/t_{ni} ~ 10 t_{ni}
(where t_{ff} is the free-fall time and t_{ni} is the neutral-ion collision
time), except that it is multiplied by a numerical factor C(\mu_{c0}), where
\mu_{c0} is the initial central mass-to-flux ratio normalized to the critical
value for gravitational collapse. C(\mu_{c0}) is typically ~ 1 in highly
subcritical clouds (\mu_{c0} << 1), although certain conditions allow
C(\mu_{c0}) >> 1. For clouds that are not highly subcritical, C(\mu_{c0}) can
be much less than unity, with C(\mu_{c0}) --> 0 for \mu_{c0} --> 1,
significantly reducing the time required to form a supercritical core. This,
along with recent observations of clouds with mass-to-flux ratios close to the
critical value, may reconcile the results of ambipolar diffusion models with
statistical analyses of cores and YSO's which suggest an evolutionary timescale
\~ 1 Myr for objects of mean density ~ 10^4 cm^{-3}. We compare our analytical
relation to the results of numerical simulations, and also discuss the effects
of dust grains on the core formation timescale.


title:
Reprocessed emission line profiles from dense clouds in geometrically
  thick accretion engines

abstract:
  The central engines of active galactic nuclei (AGN) contain cold, dense
material as well as hot X-ray emitting gas. The standard paradigm for the
engine geometry is a cold thin disc sandwiched between hot X-ray coronae.
Strong support for this geometry in Seyferts comes from the study of
fluorescent iron line profiles, although the evidence is not ubiquitously air
tight. The thin disc model of line profiles in AGN and in X-ray binaries should
be bench marked against other plausible possibilities. One proposed alternative
is an engine consisting of dense clouds embedded in an optically thin,
geometrically thick X-ray emitting engine. This model is further motivated by
studies of geometrically thick engines such as advection dominated accretion
flows (ADAFs). Here we compute the reprocessed iron line profiles from dense
clouds embedded in geometrically thick, optically thin X-ray emitting discs
near a Schwarzchild black hole. We consider a range of cloud distributions and
disc solutions, including ADAFs, pure radial infall, and bipolar outflows. We
find that such models can reproduce line profiles similar to those from
geometrically thin, optically thick discs and might help alleviate some of the
problems encountered from the latter.


title: Precessing warped accretion discs in X-ray binaries

abstract:
  We study the radiation-driven warping of accretion discs in the context of
X-ray binaries. The latest evolutionary equations are adopted, which extend the
classical alpha theory to time-dependent thin discs with non-linear warps. We
also develop accurate, analytical expressions for the tidal torque and the
radiation torque, including self-shadowing.
  We investigate the possible non-linear dynamics of the system within the
framework of bifurcation theory. First, we re-examine the stability of an
initially flat disc to the Pringle instability. Then we compute directly the
branches of non-linear solutions representing steadily precessing discs.
Finally, we determine the stability of the non-linear solutions. Each problem
involves only ordinary differential equations, allowing a rapid, accurate and
well resolved solution.
  We find that radiation-driven warping is probably not a common occurrence in
low-mass X-ray binaries. We also find that stable, steadily precessing discs
exist for a narrow range of parameters close to the stability limit. This could
explain why so few systems show clear, repeatable `super-orbital' variations.
The best examples of such systems, Her X-1, SS 433 and LMC X-4, all lie close
to the stability limit for a reasonable choice of parameters. Systems far from
the stability limit, including Cyg X-2, Cen X-3 and SMC X-1, probably
experience quasi-periodic or chaotic variability as first noticed by Wijers &
Pringle. We show that radiation-driven warping provides a coherent and
persuasive framework but that it does not provide a generic explanation for the
long-term variabilities in all X-ray binaries.


title: The X-ray Remnant of SN1987A

abstract:
  We present high resolution Chandra observations of the remnant of SN1987A in
the Large Magellanic Cloud. The high angular resolution of the Chandra X-ray
Observatory (CXO) permits us to resolve the X-ray remnant. We find that the
remnant is shell-like in morphology, with X-ray peaks associated with some of
the optical hot spots seen in HST images. The X-ray light curve has departed
from the linear flux increase observed by ROSAT, with a 0.5-2.0 keV luminosity
of 1.5 x 10^35 erg/s in January 2000. We set an upper limit of 2.3 x 10^34
ergs/s on the luminosity of any embedded central source (0.5 - 2 keV). We also
present a high resolution spectrum, showing that the X-ray emission is thermal
in origin and is dominated by highly ionized species of O, Ne, Mg, and Si.


title:
Emission Beam Geometry of Selected Pulsars Derived from Average Pulse
  Polarization Data

abstract:
  By fitting the classical Rotating Vector Model (RVM) to high quality
polarization data for selected radio pulsars, we find the inclination of the
magnetic axis to the spin axis, alpha, as well as the minimum angle between the
line of sight and the magnetic axis, beta, for ten objects. We give a full
treatment of statistical errors in the fitting process. We also present a
dictionary and conversion table of various investigators' geometric definitions
to facilitate future comparisons. We compare our results with other RVM fits
and with empirical/geometrical (E/G) approaches, and we examine the strengths
and weaknesses of RVM fits and E/G investigations for the determination of
pulsar emission beam geometry. Our fits to B0950+08 show that it is an
orthogonal rotator, contrary to previous findings. Finally, we find that RVM
fits are easily perturbed by systematic effects in polarized position angles,
and that the formal uncertainties significantly underestimate the actual
errors.


title:
Estimating Supermassive Black Hole Mass Through Radio/X-Ray Luminosity
  Relation of X-Ray Bright Galactic Nuclei

abstract:
  It has been suggested that optically thin and geometrically thick accretion
flows are responsible for the observed radio/X-ray luminosity relation of the
X-ray bright galactic nuclei. If this is the case then central supermassive
black hole masses can be estimated directly from measurements of the core radio
luminosity and the X-ray luminosity, provided that properties of such accretion
flows are known. Calculated ratios of the luminosities are presented in cases
of the standard ADAF model and modified ADAF models, in which a truncation of
inner parts of the flows and winds causing a reduction of the infalling matter
are included. We compare the observed ratio of the luminosities with
predictions from models of optically thin accretion flows. We also discuss the
possible effects of the convection in ADAFs. We confirm that the supermassive
black hole (SMBH) mass estimate is possible with the radio/X-ray luminosity
relation due to ADAF models in the absence of a radio jet. We find that
observational data are insufficient to distinguish the standard ADAF model from
its modified models. However, the ADAF model with convection is inconsistent
with observations, unless microphysics parameters are to be substantially
changed. High resolution radio observations are required to avoid the
contamination of other components, such as, a jet component. Otherwise, the
SMBH mass is inclined to be over-estimated.


title: Cosmological Perturbations with Multiple Scalar Fields

abstract:
  We consider the evolution of perturbed cosmological spacetime with multiple
scalar fields in Einstein gravity. A complete set of scalar-type perturbation
equations is presented in a gauge-ready form, and we derived the closed set of
second-order differential equations in several useful forms. Conserved
behaviors of the perturbed three-space curvature in the comoving gauge,
$\phi_v$, under several conditions are clarified. Under the slow-roll
conditions, the adiabatic and isocurvature modes decouple from each other, and
in the large-scale limit we have (i) the adiabatic mode is generally conserved,
(ii) for a couple of special potential the isocurvature modes decouple from
each other and are described by conserved quantities, (iii) in the two field
system, the isocurvature mode is described by a conserved quantity for the
general potential.


title: The Best Observables from the Point of View of a Model Maker

abstract:
  We select and discuss the best observables to be used to constrain models of
galactic chemical evolution. To this purpose, we discuss the observables in our
Galaxy, which is the best studied system, as well as in external galaxies.


title: Reconnection in a striped pulsar wind

abstract:
  It is generally thought that most of the spin-down power of a pulsar is
carried away in an MHD wind dominated by Poynting flux. In the case of an
oblique rotator, a significant part of this energy can be considered to be in a
low-frequency wave, consisting of stripes of toroidal magnetic field of
alternating polarity, propagating in a region around the equatorial plane.
Magnetic reconnection in such a structure has been proposed as a mechanism for
transforming the Poynting flux into particle energy in the pulsar wind. We have
re-examined this process and conclude that the wind accelerates significantly
in the course of reconnection. This dilates the timescale over which the
reconnection process operates, so that the wind requires a much larger distance
than was previously thought in order to convert the Poynting flux to particle
flux. In the case of the Crab, the wind is still Poynting-dominated at the
radius at which a standing shock is inferred from observation. An estimate of
the radius of the termination shock for other pulsars implies that all except
the milli-second pulsars have Poynting-flux dominated winds all the way out to
the shock front.


title: GLAST, the Gamma-ray Large Area Space Telescope

abstract:
  GLAST, a detector for cosmic gamma rays in the range from 20 MeV to 300 GeV,
will be launched in space in 2005. Breakthroughs are expected in particular in
the study of particle acceleration mechanisms in space and of gamma ray bursts,
and maybe on the search for cold dark matter; but of course the most exciting
discoveries could come from the unexpected.


title: Galactic Morphologies in Distant Clusters

abstract:
  The abundance of elliptical, S0 and spiral galaxies in clusters is presented
as a function of redshift comparing the results of the HST distant cluster
studies with new data at z~0.2 and with the standard local comparison samples.
This analysis confirms and strengthens the conclusion that the proportion of S0
galaxies increases toward lower redshifts at the expense of the spiral
population. The dependence of the relative occurrence of S0s and ellipticals
and of the morphology-density relation on the cluster concentration are also
discussed.


title:
Age-metallicity relation and Chemical evolution of the LMC from UVES
  spectra of Globular Cluster giants

abstract:
  We report on the first high-resolution spectroscopy of 10 giants in LMC
Globular Clusters in a wide age range, obtained with the newly commissioned
spectrograph UVES at VLT UT2. These observations are used to derive oxygen and
iron content of these clusters, and the abundances are then used to cast a more
precise view, not only on the age-metallicity relation in the LMC, but also on
the chemical evolution of this dwarf irregular galaxy.


title: Hierarchical Clustering and Active Galaxies

abstract:
  The growth of Super Massive Black Holes and the parallel development of
activity in galactic nuclei are implemented in an analytic code of hierarchical
clustering. The evolution of the luminosity function of quasars and AGN will be
computed with special attention paid to the connection between quasars and
Seyfert galaxies. One of the major interests of the model is the parallel study
of quasar formation and evolution and the History of Star Formation.


title:
Interpreting the kinematics of the extended gas in distant radiogalaxies
  from 8-10m telescope spectra

abstract:
  The nature of the extreme kinematics in the extended gas of distant radio
galaxies (z>0.7) is still an open question. With the advent of the 8-10 m
telescope generation and the development of NIR arrays we are in the position
for the first time to develop a more detailed study by using lines other than
Lya and [OII]3727 depending on redshift. In this paper we review the main
sources of uncertainty in the interpretation of the emission line kinematics:
the presence of several kinematic components, Lya absorption by neutral
gas/dust and the contribution of scattered light to some of the lines. As an
example, several kinematic components can produce apparent, false rotation
curves. We propose methods to solve these uncertainties. We propose to extend
the methods applied to low redshift radio galaxies to investigate the nature of
the kinematics in distant radio galaxies: by means of the spectral
decomposition of the strong optical emission lines (redshifted into the NIR) we
can isolate the different kinematic components and study the emission line
ratios for the individual components. If shocks are responsible for the extreme
kinematics, we should be able to isolate a kinematic component (the shocked
gas) with large FWHM (>900 km/s), low ionization level [OIII]5007/Hb~2-4 and
weak HeII4686/Hb<0.07, together with a narrow component (~few hundred km/s)
with higher ionization level and strong HeII emission (HeII/Hb~0.5)


title:
Origin of the scatter in the X-ray luminosity of early-type galaxies
  observed with ROSAT

abstract:
  Statistical properties of X-ray luminosity and temperature are studied for 52
early-type galaxies based on the ROSAT PSPC data. All of the X-ray luminous
galaxies show largely extended emission with a radius of a few times of
10$r_e$, while X-ray faint galaxies do not show such a component. This leads to
a division of early-type galaxies into two categories: X-ray extended and X-ray
compact galaxies. Except for a few galaxies in dense cluster environments, the
luminosity and temperature of X-ray compact galaxies are well explained by a
kinematical heating of the gas supplied by stellar mass loss. In contrast,
X-ray extended galaxies indicate large scatter in the X-ray luminosity. We
discuss that X-ray extended galaxies are the central objects of large potential
structures, and the presence and absence of this potential is the main origin
of the large scatter in the X-ray luminosity.


title: Complex Visibilities of Cosmic Microwave Background Anisotropies

abstract:
  We study the complex visibilities of the cosmic microwave background
anisotropies that are observables in interferometric observations of the cosmic
microwave background, using the multipole expansion methods commonly adopted in
analyzing single-dish experiments. This allows us to recover the properties of
the visibilities that is obscured in the flat-sky approximation. Discussions of
the window function, multipole resolution, instrumental noise, pixelization,
and polarization are given.


title:
Astrometric demands of fibre-input spectrographs for wide-field quasar
  redshift surveys

abstract:
  A potential problem with using wide-field multi-object spectrographs for
quasar redshift surveys is the introduction of position-dependent selection
effects into the survey catalogue because of variations in the observed
signal-to-noise ratio (SNR) across the survey area. A function relating signal
losses in instruments using optical fibre input to the fibre-to-image position
error, the fibre diameter and the seeing conditions is given and plotted for a
range of typical values of fibre sizes and seeing found in current instruments.


title: Strange Pathways for Black Hole Formation

abstract:
  Immediately after they are born, neutron stars are characterized by an
entropy per baryon of order unity and by the presence of trapped neutrinos. If
the only hadrons in the star are nucleons, these effects slightly reduce the
maximum mass relative to cold, catalyzed matter. However, if stangeness-bearing
hyperons, a kaon condensate, or quarks are also present, these effects result
in an increase in the maximum mass of up to $\sim 0.3{\rm M}_{\odot}$ compared
to that of a cold, neutrino-free star. This makes a sufficiently massive
proto-neutron star metastable, so that after a delay of 10--100 seconds, the
PNS collapses into a black hole. Such an event might be straightforward to
observe as an abrupt cessation of neutrinos when the instability is triggered.


title: The Star Clusters in the Starburst Irregular Galaxy NGC 1569

abstract:
  We examine star clusters in the irregular, starburst galaxy NGC 1569 from HST
images. In addition to the two known super star clusters, we identify 45 other
clusters that are compact but resolved. Integrated UVI colors of the clusters
span a large range, and suggest that ages range from 3 Myrs to 1 Gyr. However,
most of the clusters were formed at the tail end of the recent starburst.
Numerous clusters in addition to the know super star clusters are similar in
luminosity to a small globular cluster. We examined the radial surface
brightness of four of the clusters. Their half-light radii and core radii are
in the range observed in present-day globular clusters. Therefore, conditions
that produced the recent starburst have also been those necessary for producing
compact, bright star clusters.
  We examine resolved stars in the outer parts of the two super star clusters.
Cluster A is dominated by bright blue stars with a small population of red
supergiants. Sub-components A1 and A2 have similar colors and a two-dimensional
color map does not offer evidence that one component is dominated by red
supergiants and the other not. The contradiction of the presence of red super-
giants with Wolf-Rayet stars may instead not be a contradiction at all since
there coexistence in a coeval population is not inconsistent with the evolution
of massive stars. Cluster B is dominated by red supergiants, and this is
confirmed by the presence of the stellar CO absorption feature in an integrated
spectrum. The various age indicators are consistent with a picture in which
cluster B is of order 10--20 Myrs old, and cluster A is >4-5 Myrs old.


title:
The Razor's Edge: Magnetic Fields and Their Fundamental Role in Star
  Formation and Observations of Protostellar Coress

abstract:
  We review theoretical models of the early stages of star formation, in which
gravitational collapse is strongly regulated by magnetic fields and the
associated process of ambipolar diffusion. We discuss results of numerical
simulations and analytical studies of core formation and collapse, which can be
directly tested against observation. We also focus on recent data which are
relevant to this theory of star formation, such as: observations of extended
infall in protostellar cores, estimates of evolutionary timescales ~ 1 Myr for
cores, measured mass-to-flux ratios of cores, and the relative alignment of
polarization vectors with apparent cloud elongation. It is shown that in all of
these areas, the data lie within the observationally allowable range of
parameter space. Other areas of interest (protostellar accretion rates and the
presence of core edges) and issues that remain unresolved or under study (the
role of non-thermal motions and cluster formation) are also discussed.
Moreover, we highlight some differences between our model predictions and those
of highly turbulent star formation models, and discuss how these differences
can be distinguished observationally.


title: Rapidly rotating strange stars

abstract:
  We study effects of the strange quark mass and of the QCD coupling constant
in the MIT bag model of quark matter with lowest order quark-gluon interactions
on the rapid rotation of strange stars. The influence of rotation on global
parameters of strange stars is greater than in the case of the neutron star
models. We show that independently of the strange quark mass and the coupling
constans the ratio of the rotational kinetic energy to the absolute value of
the gravitational potential energy for rotating strange stars is significantly
higher than for ordinary neutron stars. This might indicate that rapidly
rotating strange stars could be important sources of gravitational waves.


title:
The magnetorotational instability across the dead zone of protoplanetary
  disks

abstract:
  We examine the linear stability of a flow threaded by a weak, vertical
magnetic field in a disk with a keplerian rotation profile and a vertical
stratification of the ionization degree as that predicted for vast portions of
protoplanetary disks. A quasi-global analysis is carried out, where the form of
the perturbations in the vertical direction is determined. Considering the
ohmic magnetic diffusivity of the gas, the conditions leading to the
magnetorotational instability are analyzed as a function of the diffusivity at
the disk surfaces, its vertical profile and the strength of the unperturbed
magnetic field. For typical conditions believed to prevail in protoplanetary
disks at radial distances between 0.1 and 10 AU, where the so-called dead zone
is proposed to exist, we find that generally the instability is damped. This
implies that, if the MRI is considered the only possible source of turbulence
in protoplanetary disks, no viscous angular momentum transport occursat those
radii.


title:
Interstellar Gas and Star Formation Near the Peculiar Radio Galaxy NGC
  4410A

abstract:
  We present new multi-wavelength data for the NGC 4410 galaxy group. This
group contains the peculiar radio galaxy NGC 4410A, which has a distorted
double-lobed radio structure. NGC 4410A is strongly interacting with three
nearby galaxies, and has a peculiar ring-like optical morphology, a number of
luminous H II regions, as well as as tidal tails and bridges variously visible
in optical, HI, and X-ray light. The gravitational interaction has affected the
interstellar matter, the star formation rate, and the radio lobes in this
system.