Astrophysics

astro-ph new abstracts, Wed, 23 Aug 00 04:00:13 GMT
0008329 — 0008350 received

astro-ph/0008329 [abs, src, ps, other] :

Title: Statistical lensing constraints on the shape of galaxy halos
Authors:
D. Rusin,
Max Tegmark
Comments: 24 pages, including 7 figures

The relative frequency of four-image gravitational lens systems is an
excellent tool for testing assumptions regarding the characteristic flattening
of galaxy mass distributions. Using a sample of sixteen radio-loud
gravitational lenses from the JVAS/CLASS survey and assuming the statistically
negligible external shears predicted by the galaxy-galaxy correlation function,
the hypothesis that the mass and light of galaxies follow the same ellipticity
distribution is ruled out at about 98%, even in the presence of rather large
core radii and a simple dynamical correction that increases the influence of
flattened deflectors. We find that a typical projected axial ratio of 0.30 < f
< 0.61 (95%) is favored by the lensing multiplicity data for small core models
in this scenario. While observations suggest that external shear and compound
deflectors influence gravitational lensing at a far greater level than is
currently predicted, a subsample of lenses that appear to be free of these
effects still shows a statistically significant over-representation of
four-image systems, favoring a projected axial ratio of 0.24 < f < 0.64 (95%)
for small cores. These findings argue that external shear alone is unlikely to
account for the large number of quads, and that galaxy halos may be playing an
important role.
(427kb)

astro-ph/0008330 [abs, src, ps, other] :

Title: A Test for the Nature of the Type Ia Supernova Explosion Mechanism
Authors:
Philip A. Pinto (1),
Ronald G. Eastman (2),
Tamara Rogers (3) ((1) Steward Observatory, Univ. of Arizona, (2) Lawrence Livermore National Laboratory, (3) Lick Observatory, University of California, Santa Cruz)
Comments: 30 pages, 17 figures

Currently popular models for Type Ia supernovae (SNe Ia) fall into two
general classes. The first comprises explosions of nearly pure carbon/oxygen
(C/O) white dwarfs at the Chandrasekhar limit which ignite near their centers.
The second consists of lower-mass C/O cores which are ignited by the detonation
of an accreted surface helium layer. Explosions of the latter type produce
copious Fe, Co and Ni K-alpha emission from 56Ni and 56Co decay in the
detonated surface layers, emission which is much weaker from Chandrasekhar-mass
models. The presence of this emission provides a simple and unambiguous
discriminant between these two models for SNe Ia. Both mechanisms may produce
0.1-0.6 solar masses of 56Ni, making them bright gamma-ray line emitters. The
time to maximum brightness of 56Ni decay lines is distinctly shorter in the
sub-Chandrasekhar mass class of model (approximately 15 days) than in the
Chandrasekhar mass model (approximately 30 days), making gamma-ray line
evolution another direct test of the explosion mechanism. It should just be
possible to detect K-shell emission from a sub-Chandrasekhar explosion from SNe
Ia as far away as the Virgo cluster with the XMM Observatory. A 1 to 2 square
meter X-ray telescope such as the proposed Con-X Observatory could observe
K-alpha emission from sub-Chandrasekhar mass SNe Ia in the Virgo cluster,
providing not just a detection, but high-accuracy flux and kinematic
information.
(190kb)

astro-ph/0008331 [abs, src, ps, other] :

Title: Discovery of a Slow X-Ray Pulsator, AX J1740.1-2847, in the Galactic
Center Region
Authors:
Masaaki Sakano (1),
Ken’ichi Torii (1),
Katsuji Koyama (2 and 3),
Yoshitomo Maeda (4),
Shigeo Yamauchi (5) ((1) NASDA (2) Dept. Phys., Kyoto Univ. (3) CREST (4) Penn-State Univ. (5) Iwate Univ.)
Comments: To appear in PASJ Dec. 25, 2000 issue, Vol.52 No.6; 5 pages LaTeX
files, uses PASJ95.sty, PASJadd.sty, psfig.sty; also available at
this http URL

We report the discovery of an X-ray pulsar AX J1740.1-2847 from the Galactic
center region. This source was found as a faint hard X-ray object on 7–8

September 1998 with the ASCA Galactic center survey observation. Then,
coherent pulsations of P=729 +/- 14 sec period were detected. The

X-ray spectrum is described by a flat power-law of ~= 0.7 photon index. The
large absorption column of log NH ~= 22.4

(cm^-2) indicates that AX J1740.1-2847 is a distant source, larger than 2.4
kpc, and possibly near at the Galactic center region. The luminosity in the
2–10 keV band is larger than 2.5 x 10^33 erg/s, or likely to be 3.2 x 10^34
erg/s at the Galactic center distance. Although the slow pulse period does not
discriminate whether AX J1740.1-2847 is a white dwarf or neutron star binary,
the flat power-law and moderate luminosity strongly favor a neutron star
binary.
(86kb)

astro-ph/0008332 [abs, src, ps, other] :

Title: Comparison of the Two Followup Observation Strategies for Gravitational
Microlensing Planet Searches
Authors:
Cheongho Han,
Yong-Gi Kim (Chungbuk National University, Korea)
Comments: total 5 pages, including 3 figures and 1 table, ApJ, submitted
Journal-ref: CNU-A&SS-08/2000

There are two different strategies of followup observations for the detection
of planets by using microlensing. One is detecting the light curve anomalies
affected by the planetary caustic from continuous monitoring of all events
detected by microlensing survey programs (type I strategy) and the other is
detecting anomalies near the peak amplification affected by the central caustic
from intensive monitoring of high amplification events (type II strategy). It
was shown by Griest & Safizadeh that the type II strategy yields high planet
detection efficiency per event. However, it is not known the planet detection
rate by this strategy can make up a substantial fraction of the total rate. In
this paper, we estimate the relative planet detection rates expected under the
two followup observation strategies. From this estimation, we find that the
rate under the type II strategy is substantial and will comprise $sim 1/4$ —
1/2 of the total rate. We also find that compared to the type I strategy the
type II strategy is more efficient in detecting planets located outside of the
lensing zone. We determine the optimal monitoring frequency of the type II
strategy to be $sim 20$ times/night, which can be easily achieved by the
current microlensing followup programs even with a single telescope.
(119kb)

astro-ph/0008333 [abs, src, ps, other] :

Title: Radio Halos of Galaxy Clusters from Hadronic Secondary Electron
Injection in Realistic Magnetic Field Configurations
Authors:
Klaus Dolag,
Torsten A. Ensslin
Comments: 7 pages, 6 figures, accepted for publication in Astronomy and
Astrophysics

We investigate the possibility that radio halos of clusters of galaxies are
caused by synchrotron emission of cosmic ray electrons (CRe), which were
produced by cosmic ray protons (CRp) interacting hadronically with the
intra-cluster medium (ICM) protons. We perform cosmological
magneto-hydrodynamics (MHD) simulations to obtain a sample of ten magnetized
galaxy clusters. They provide realistic models of the gas and magnetic field
distribution, needed to predict the CRe production rates, their cooling, and
their synchrotron emissivity. We assume a CRp population within the ICM with an
energy density which has a constant ratio to thermal energy density. This ratio
is adjusted in such a way that one of the simulated clusters reproduces the
radio luminosity of the radio halo of the Coma cluster of galaxies. Our model
exhibits the observed low degree of radio polarization and has a similar radial
emission profile as the Coma cluster. We provide estimates for the expected
gamma ray and neutrino flux. The necessary CRp/thermal energy ratio is 4 …
14% ${(E_{p,min}/GeV)}^{-0.375}$ (for the range of magnetic field strengths
suggested by Faraday measurements), where $E_{p,min}$ is the lower kinetic
energy cutoff of the CRp with spectral index $alpha_p approx 2.375$. Assuming
this ratio to be the same in the whole set of simulated clusters a $T_x-L_
u$
relation is predicted which follows the observed relation well.
(45kb)

astro-ph/0008334 [abs, src, ps, other] :

Title: Phenomenon of Gamma-Ray Bursts as Relativistic Detonation of Scalar
Fields
Authors:
V. Folomeev,
V.Gurovich,
R. Usupov
Comments: LaTex, 7 pages, 2 figures

In the modern Universe the existence of various forms of scalar fields is
supposed. On the one hand these fields can explain recently discovered positive
$Lambda$-term(see e.g. Ref. cite{ref:Sahni}), on the other hand its form
cluster systems creating gravitational wells for galaxies and their clusters.
At that a natural hypothesis is the existence of compact configurations
(“stars”) from scalar fields with a large enough energy density and total mass.
The hypothesis is that the energy of these fields can be converted in
relativistic plasma by an explosive way. Such process can be initiated by
collision of relativistic particles which form a relativistic microscopic
fireball. Thus effective temperature can amount to value sufficient for change
of phase for scalar fields. Then the wave of relativistic “detonation” similar
to the same process in classical physics will be spread from this source. In
this paper the parameters of such field star and process of detonation are
estimated. If the effect of the indicated change of phase (or something similar
to one) exists, it is possible to get the parameters of relativistic plasma
(macroscopic fireball) which could generate gamma – bursts. If in the modern
Universe there is such unique form of a matter as fields of high density it
would be strange for Nature not to take advantage of the possibility to convert
their energy to radiation by an explosive way.
(27kb)

astro-ph/0008335 [abs, src, ps, other] :

Title: Unidentified Infrared Emission Bands in the Diffuse Interstellar Medium
Authors:
Kin-Wing Chan,
T. L. Roellig,
T. Onaka,
M. Mizutani,
K. Okumura,
I. Yamamura,
T. Tanabe,
H. Shibai,
T. Nakagawa,
H. Okuda
Comments: 13 pages, 6 figures. Accepted for publication in ApJ

Using the Mid-Infrared Spectrometer on board the Infrared Telescope in Space
and the low-resolution grating spectrometer (PHT-S) on board the Infrared Space
Observatory, we obtained 820 mid-infrared (5 to 12 $mu$m) spectra of the
diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina
Nebula regions. These spectra indicate that the emission is dominated by the
unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 $mu$m.
The relative band intensities (6.2/7.7 $mu$m, 8.6/7.7 $mu$m, and 11.2/7.7
$mu$m) were derived from these spectra, and no systematic variation in these
ratios was found in our observed regions, in spite of the fact that the
incident radiation intensity differs by a factor of 1500. Comparing our results
with the polycyclic aromatic hydrocarbons (PAHs) model for the UIR band
carriers, PAHs in the DIM have no systematic variation in their size
distribution, their degree of dehydrogenation is independent of the strength of
UV radiation field, and they are mostly ionized. The latter finding is
incompatible with past theoretical studies, in which a large fraction of
neutral PAHs is predicted in this kind of environment. A plausible resolution
of this discrepancy is that the recombination coefficients for electron and
large PAH positive ion are by at least an order of magnitude less than those
adopted in past theoretical studies. Because of the very low population of
neutral state molecules, photoelectric emission from interstellar PAHs is
probably not the dominant source of heating of the diffuse interstellar gas.
The present results imply constant physical and chemical properties of the
carriers of the UIR emission bands in the DIM.
(47kb)

astro-ph/0008336 [abs, src, ps, other] :

Title: The impact of chemical evolution on the observable properties of stellar
populations
Author:
M.Tosi (Osservatorio Astronomico di Bologna)
Comments: 10 pages, 7 encapsulated figs. Review paper to appear in ‘The
Evolution of Galaxies. I. Observational Clues’, J.M. Vilchez, G.Stasinska and
E. Perez eds. (Kluwer, Dordrecht) in press

The major effects of the chemical evolution of galaxies on the
characteristics of their stellar populations are reviewed. A few examples of
how the observed stellar properties derived from colour–magnitude diagrams can
constrain chemical evolution models are given.
(265kb)

astro-ph/0008337 [abs, src, ps, other] :

Title: Cosmological Relativity: A General-Relativistic Theory for the
Accelerating Expanding Universe
Authors:
M. Carmeli,
S. Behar

Recent observations of distant supernovae imply, in defiance of expectations,
that the universe growth is accelerating, contrary to what has always been
assumed that the expansion is slowing down due to gravity. In this paper a
general-relativistic cosmological theory that gives a direct relationship
between distances and redshifts in an expanding universe is presented. The
theory is actually a generalization of Hubble’s law taking gravity into account
by means of Einstein’s theory of general relativity. The theory predicts that
the universe can have three phases of expansion, decelerating, constant and
accelerating, but it is shown that at present the first two cases are excluded,
although in the past it had experienced them. Our theory shows that the
universe now is definitely in the stage of accelerating expansion, confirming
the recent experimental results.
(100kb)

astro-ph/0008338 [abs, src, ps, other] :

Title: Discovery of a New Supernova Remnant in the Direction of G69.7+1.0
Authors:
Kumi Yoshita,
Emi Miyata,
Hiroshi Tsunemi (Osaka University)
Comments: Accepted for publication in PASJ, 9 pages, 5 figures

We discovered a middle-aged supernova remnant (SNR) in the vicinity of
G69.7+1.0 using the ASCA satellite. G69.7+1.0 was identified in the 2.7 GHz
survey and classified as a shell-type SNR with a diameter of 16 arcmin. During
the ROSAT all-sky survey, the X-ray emission was detected in the direction of
G69.7+1.0. However, it extends beyond the radio shell, and an X-ray bright
region was located outside of the radio shell. A spectral study with the ASCA
and ROSAT shows a thin thermal plasma with an electron temperature of ~0.4 keV.
There is no significant variation of the spectral parameters over the field of
view, except for the lower column density of the eastern part. We also found a
large shell structure which surrounds the X-ray bright region in both optical
and radio images. We suggest that the observed X-ray emission is associated
with the large optical and radio shell, and that they are part of a new SNR,
different from the radio SNR G69.7+1.0, which we have named AX J2001+3235 or
G69.4+1.2. The large shell and the electron temperature of ~0.4 keV indicate
that AX J2001+3235 is an evolved SNR. From a comparison with the column density
of CTB 80 (G69.0+2.7), we estimate that the distance of the SNR is about 2.5
kpc.
(325kb)

astro-ph/0008339 [abs, src, ps, other] :

Title: First Results from the Heidelberg Dark Matter Search Experiment
Authors:
L. Baudis,
A. Dietz,
B. Majorovits,
F. Schwamm,
H. Strecker,
H. V. Klapdor-Kleingrothaus
Comments: 11 pages, latex, 4 tables, 10 figures; submitted to Phys. Rev. D

The Heidelberg Dark Matter Search Experiment (HDMS) is a new ionization
Germanium experiment in a special design. Two concentric Ge crystals are housed
by one cryostat system, the outer detector acting as an effective shield
against multiple scattered photons for the inner crystal, which is the actual
dark matter target. We present first results after successfully running the
prototype detector for a period of about 15 months in the Gran Sasso
Underground Laboratory. We analyze the results in terms of limits on
WIMP-nucleon cross sections and present the status of the full scale
experiment, which will be installed in Gran Sasso in the course of this year.
(312kb)

astro-ph/0008340 [abs, src, ps, other] :

Title: Spectroscopy of diffuse ionized gas in halos of selected edge-on
galaxies
Authors:
R. Tuellmann,
R.-J. Dettmar (Astronomisches Institut, Ruhr-Universitaet Bochum, Germany)
Comments: Accepted for publication in A&A, 15 pages, 17 figures. For high
resolution ps-files, see this http URL

In order to examine the excitation and ionization mechanism of extraplanar
diffuse ionized gas (DIG) we have obtained optical longslit spectra of seven
edge-on spiral galaxies. In four objects the brightest emission lines can be
traced out to distances of typically 1.5 kpc above the disk. For NGC1963 and
NGC3044 line ratios such as [NII]6583/Ha or [SII]6717/Ha as well as
[OIII]5007/Hb could be measured for the halo DIG. This allows us to discuss the
DIG in the halo of these objects in the framework of diagnostic diagrams. For
these two objects, the line ratios of [OIII]5007/Hb decrease with increasing z,
different from the recently reported trend in NGC891 (Rand 1998). We find that
emission lines from the DIG in the disks are in good agreement with
photoionization models using a dilute radiation field. However, with increasing
z these models fail to predict the measured [OI]6300/Ha and HeI5876/Ha line
ratios for NGC1963. Diagnostic diagrams reveal for NGC1963 the need for a
second ionization mechanism of the halo DIG (besides photoionization). This
additional source could be shock ionization. The same diagrams demonstrate an
intermediate classification for NGC3044. Plots of [SII]/[NII] vs. emission
measure reveal significant changes towards the halo and seem to trace local
small scale density fluctuations of the extraplanar DIG.
(393kb)

astro-ph/0008341 [abs, src, ps, other] :

Title: Dynamical Evolution: Spirals and Bars
Authors:
F.Combes (DEMIRM, Paris Observatory)
Comments: 8 pages, 5 figures, to appear in ASP Conference Series, “Galaxy Disks
and Disk Galaxies”, J.G. Funes S.J. and E.M. Corsini, eds

Non-axisymmetric modes like spirals and bars are the main driver of the
evolution of disks, in transferring angular momentum, and allowing mass
accretion. This evolution proceeds through self-regulation and feedback
mechanisms, such as bar destruction or weakening by a central mass
concentration, decoupling of a nuclear bar taking over the gas radial flows and
mass accretion, etc.. These internal mechanisms can also be triggered by
interaction with the environment. Recent problems are discussed, like the
influence of counter-rotation in the m=1 and m=2 patterns development and on
mass accretion by a central AGN.
(449kb)

astro-ph/0008342 [abs, src, ps, other] :

Title: Halo and Relic Sources in Clusters of Galaxies
Authors:
G. Giovannini,
L. Feretti
Comments: 16 Figures in separated files. A large ps file with figures
(gg-aug00.ps.gz) in the text is avaialble at
this ftp URL New Astronomy Vol. 5, p.335, in press

New images of 7 radio halos and relics, obtained with the Very Large Array at
20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in
the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the
properties of the other clusters with radio halos, i.e. are luminous in X-rays,
have high temperature, and show recent merger processes. No diffuse sources are
detected in a sample of clusters showing at least a tailed radio galaxy within
300 kpc from the cluster center, indicating that the connection between tailed
radio galaxies and halos is not relevant. For these clusters we give limits to
the surface brightness and to the angular size of possible undetected diffuse
sources.
(717kb)

astro-ph/0008343 [abs, src, ps, other] :

Title: Flat radio-spectrum galaxies and BLLacs: Part I: core properties
Authors:
J.Dennett-Thorpe,
M.J. Marcha
Comments: Accepted A&A. 13 pages

This paper concerns the relationship of BLLacs and flat spectrum weak
emission-line galaxies. We compare the weak emission-line galaxies and the
BLLacs in a sample of 57 flat spectrum objects (Marcha et al. 1996), using
high-frequency radio and non-thermal optical flux densities, spectral indices
and polarization properties. We consider whether objects which are not
`traditional’ BLLacs-due to their larger emission line strengths, and larger
CaII spectral breaks-are simply starlight diluted BLLacs. Their broad-band
spectral properties are consistent with this interpretation, but their radio
polarization may indicate more subtle effects. Comparison of the weak
emission-line galaxies and the BLLacs shows that, on average, the former have
steeper spectra between 8 and 43GHz, and are less polarized at 8.4GHz. This is
consistent with many of the weak-lined objects being at larger angles to the
line of sight than the BLLacs. In addition to this population, we indicate a
number of the weak emission-line galaxies which may be `hidden BLLacs’:
relativistically boosted objects very close to the line of sight with an
apparently weak AGN.
(49kb)

astro-ph/0008344 [abs, src, ps, other] :

Title: Thermal X-ray Emission and Cosmic Ray Production in Young Supernova
Remnants
Authors:
A. Decourchelle,
D.C. Ellison,
J. Ballet
Comments: 4 pages, 3 figures, submitted to ApJ Letters

We have developed a simple model to investigate the modifications of the
hydrodynamics and non-equilibrium ionization X-ray emission in young supernova
remnants due to nonlinear particle acceleration. In nonlinear, diffusive shock
acceleration, the heating of the gas to X-ray emitting temperatures is strongly
coupled to the acceleration of cosmic ray ions. If the acceleration is
efficient and a significant fraction of the shock ram energy ends up in cosmic
rays, compression ratios will be higher and the shocked temperature lower than
test-particle, Rankine-Hugoniot relations predict. In this Letter, we show that
typical parameters of young supernova remnants should result in significant
nonlinear acceleration, which strongly modifies the hydrodynamics and
consequently the thermal X-ray emission. We illustrate how particle
acceleration impacts the interpretation of X-ray data using the X-ray spectra
of Kepler’s remnant, observed by {it ASCA} and {it RXTE}. We show that
thermal X-ray emission provides important constraints on the efficiency of
particle acceleration, in complement to nonthermal emission. X-ray data from
{it Chandra} and {it XMM Newton}, plus radio observations, will be essential
to quantify nonlinear effects.
(40kb)

astro-ph/0008345 [abs, src, ps, other] :

Title: A new look at globular cluster colors in NGC 3311 and the case for
exclusively metal-rich globular cluster systems
Authors:
Jean P. Brodie (1),
Soeren S. Larsen (1),
Markus Kissler-Patig (2) ((1) UCO/Lick Observatory, (2) ESO)
Comments: 11 pages, 2 figures, accepted for publication in ApJ Letters

NGC 3311, the central cD galaxy in the Hydra cluster, was previously thought
to host the most metal-rich globular cluster system known. Ground-based
Washington photometry had indicated the almost complete absence of the
population of globular clusters near [Fe/H] ~ -1 dex, normally dominant in the
metallicity distribution functions of giant elliptical galaxies. Lacking the
normal metal-poor globular cluster population, NGC 3311 was an outstanding
exception among galaxies, not easily understood under any of the current
globular cluster formation scenarios. Our HST/WFPC2 data yield normal globular
cluster colors and hence metallicities for this galaxy. We find a bi-modal
color distribution with peaks at (V-I)=0.91 +/- 0.03 and 1.09 +/- 0.03,
corresponding to [Fe/H] ~ -1.5 and -0.75 dex (somewhat dependent on the choice
of the conversion relation between color and metallicity). We review the
evidence for exclusively metal-rich globular cluster systems in other galaxies
and briefly discuss the implications for our understanding of globular cluster
and galaxy formation.
(100kb)

astro-ph/0008346 [abs, src, ps, other] :

Title: X-ray Emission from Isolated Be Stars
Authors:
David H. Cohen
Comments: To appear in A.S.P. conf. ser. 214, The Be Phenomenon in Early-Type
Stars, eds. Smith, Henrichs, Fabregat; Also available at
this http URL

I discuss the X-ray observations of Be stars, and how their properties
compare to non-emission B stars. I focus on several specific stars that show
high flux levels and variability but also report on several interesting survey
results. The Be X-ray properties are discussed in the context of wind-shock
X-ray emission from normal OB stars as well as in the context of general
mechanisms that have been proposed to explain the Be phenomenon. Finally, I
conclude with a discussion of the spectral diagnostics that will be available
from the new generation of X-ray telescopes.
(49kb)

astro-ph/0008347 [abs, src, ps, other] :

Title: Atomic and Molecular Gas near NGC3077: The Making of a New Dwarf
Galaxy?
Authors:
Fabian Walter,
Andreas Heithausen
Comments: Conference Proceedings “HI in the Local Universe II”, Guanajuato,
Mexico, 2000

Using the IRAM 30m radio telescope we have mapped the tidal arm feature
south-east of NGC 3077 where we recently detected molecular gas in the CO (1-0)
and (2-1) transitions. We find that the molecular gas is much more extended
than previously thought (several kpc). The CO emission can be separated into at
least 3 distinct complexes with equivalent radii between 250pc and 700pc – the
newly detected complexes therefore range among the largest molecular complexes
in the local universe. Mass estimates based on virialization and employing an
X_CO factor yield a total mass for the complexes of order 4 x 10^7 M_sun, i.e.
more than the estimated molecular mass within NGC 3077 itself. This implies
that interactions between galaxies can efficiently remove heavy elements and
molecules from a galaxy and enrich the intergalactic medium. A comparison of
the distribution of HI and CO shows no clear correlation. However, CO is only
found in regions where the HI column density exceeds 1.1 x 10^21 cm^-2. HI
masses for the molecular complexes mapped are of the same order as the
corresponding molecular masses. Since the complexes have all the ingredients to
form stars in the future, we are thus presumably witnessing the birth of a
dwarf galaxy. This process may have dominated the creation of dwarf galaxies at
larger look-back times.
(166kb)

astro-ph/0008348 [abs, src, ps, other] :

Title: Orbit Fitting and Uncertainties for Kuiper Belt Objects
Authors:
G. Bernstein,
B. Khushalani
Comments: 21 pages AASTeX5, 3 figures, accepted to AJ. Associated software
available at this http URL

We present a procedure for determination of positions and orbital elements,
and associated uncertainties, of outer Solar System planets. The orbit-fitting
procedure is greatly streamlined compared to traditional methods because
acceleration can be treated as a perturbation to the inertial motion of the
body. These techniques are immediately applicable to Kuiper Belt Objects, for
which recovery observations are costly. Our methods produce positional
estimates and uncertainty ellipses even in the face of the substantial
degeneracies of short-arc orbit fits; the sole a priori assumption is that the
orbit should be bound or nearly so. We use these orbit-fitting techniques to
derive a strategy for determining Kuiper Belt orbits with a minimal number of
observations.
(364kb)

astro-ph/0008349 [abs, src, ps, other] :

Title: Interstellar X-ray Absorption Spectroscopy of Oxygen, Neon, and Iron
with the Chandra LETGS Spectrum of X0614+091
Authors:
Frits Paerels,
A. C. Brinkman,
R. L. J. van der Meer,
J. S. Kaastra,
E. Kuulkers,
A. J. F. den Boggende,
P. Predehl,
Jeremy J. Drake,
Steven M. Kahn,
Daniel W. Savin,
Brendan M. McLaughlin
Comments: 16 pages, 4 figures; ApJ, accepted

We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the
Chandra Low Energy Transmission Grating Spectrometer spectrum of the low mass
X-ray binary X0614+091. We measure the column densities in O and Ne, and find
direct spectroscopic constraints on the chemical state of the interstellar O.
These measurements probably probe a low-density line of sight through the
Galaxy and we discuss the results in the context of our knowledge of the
properties of interstellar matter in regions between the spiral arms.
(61kb)

astro-ph/0008350 [abs, src, ps, other] :

Title: Intermittent behavior of cosmic mass field revealed by QSO’s Ly_alpha
forests
Authors:
Priya Jamkhedkar,
Hu Zhan,
Li-Zhi Fang
Comments: Accepted for publication in ApJ Letters, 12 pages, 3 figures

The intermittent behavior of the space-scale distribution of Ly$alpha$
transmitted flux of QSO HS1700+64 has been analyzed via a discrete wavelet
transform. We found that there are strong indications of intermittency on
scales down to about 10 $h^{-1}$ kpc. These are: 1.) the probability
distribution function of the local fluctuations of the flux is significantly
long-tailed on small scales, and 2.) the local power spectrum of the flux shows
prominent spiky structures on small scales. Moreover, the local power spectrum
averaged on regions with different sizes shows similar spiky structures.
Therefore, the random mass density field traced by the Ly$alpha$ forests is
rougher on smaller scales, consistent with singular clustering.
(27kb)

Cross-listings

hep-ph/0008215 [abs, src, ps, other] :

Title: Discovery of a new particle named a coretron and a non-baryionic dark
matter
Authors:
J.K. Hwang
Comments: 4 pages, 3 figures

A new particle named a coretron is reported as non-baryionic in the present
work. The C-fermion (a coretron fermion) is identified as the lightest
supersymmetric particle (LSP). This particle is understood as a best candidate
of the non-baryonic dark matter and an origin of the matter. If the concept of
the present coretron is, succesfully, included in the Standard model, several
top questions such as the gravity strength, the dominance of the matter in our
cosmos, a property of the large blackhole, et al. could be solved, too.
(41kb)

Replacements

astro-ph/0005233 [abs, src, ps, other] :

Title: What Does It Take to Stabilize Gravitational Clustering?
Authors:
Chung-Pei Ma (U. Penn.),
J. N. Fry (U. Florida)
Comments: Final version appeared in ApJ Lett. (August 1 2000); Minor revisions;
10 pages, 2 inserted postscript figures
Journal-ref: Astrophys. J. 538 (2000) L107-L111
Note: replaced with revised version Tue, 22 Aug 2000 00:18:47 GMT (16kb)

astro-ph/0006073 [abs, src, ps, other] :

Title: Transport phenomena in stochastic magnetic mirrors
Authors:
Leonid Malyshkin,
Russell Kulsrud
Comments: 25 pages, 7 figures, 3 appendices
Subj-class: Astrophysics; Plasma Physics
Note: replaced with revised version Tue, 22 Aug 2000 02:14:38 GMT (95kb)

astro-ph/0007247 [abs, src, ps, other] :

Title: Cosmic Inflation
Authors:
Andreas Albrecht
Comments: Lectures presented at the NATO Advanced Studies Institute “Structure
Formation in the Universe”, Cambridge 1999. To be published by Kluwer, R.
Crittenden and N. Turok Eds. 28 Pages including 13 figures. 2nd verision
includes a couple of additional references (Including the excellent new book
by Liddle and Lyth) but is otherwise unchanged
Note: replaced with revised version Tue, 22 Aug 2000 22:55:06 GMT (349kb)

hep-th/0003076 [abs, src, ps, other] :

Title: Holographic RG and Cosmology in Theories with Quasi-Localized Gravity
Authors:
Csaba Csaki,
Joshua Erlich,
Timothy J. Hollowood,
John Terning
Comments: 19 pages, LaTeX, 2 figures, requires JHEP.cls, significant changes:
effects of induced boundary operators included
Note: replaced with revised version Tue, 22 Aug 2000 21:22:37 GMT (30kb) 
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