Astrophysics

astro-ph new abstracts, Fri, 8 Sep 00 04:00:11 GMT
0009102 — 0009124 received

astro-ph/0009102 [abs, src, ps, other] :

Title: Optical Spectra of Type Ia Supernovae at z=0.46 and z=1.2

Authors:
Alison L. Coil,
Thomas Matheson,
Alexei V. Filippenko,
Douglas C. Leonard,
John Tonry,
Adam G. Riess,
Peter Challis,
Alejandro Clocchiatti,
Peter M. Garnavich,
Craig J. Hogan,
Saurabh Jha,
Robert P. Kirshner,
B. Leibundgut,
M. M. Phillips,
Brian P. Schmidt,
Robert A. Schommer,
R. Chris Smith,
Alicia M. Soderberg,
J. Spyromilio,
Christopher Stubbs,
Nicholas B. Suntzeff,
Patrick Woudt

Comments: 6 pages including 2 figures; to appear in The Astrophysical Journal
Letters

We present optical spectra, obtained with the Keck 10-m telescope, of two
high-redshift type Ia supernovae (SNe Ia) discovered by the High-z Supernova
Search Team: SN 1999ff at z=0.455 and SN 1999fv at z~1.2, the highest-redshift
published SN Ia spectrum. Both SNe were at maximum light when the spectra were
taken. We compare our high-z spectra with low-z normal and peculiar SNe Ia as
well as with SNe Ic, Ib, and II. There are no significant differences between
SN 1999ff and normal SNe Ia at low redshift. SN 1999fv appears to be a SN Ia
and does not resemble the most peculiar nearby SNe Ia.
(64kb)

astro-ph/0009103 [abs, src, ps, other] :

Title: Cerenkov Line-like Radiation, The Extended and Improved Formulae System

Authors:
J.H.You,
Y.D. Xu,
D.B.Liu,
J.R.Shi,
G.X.Jin

Comments: accepted for publication in A&A

You & Cheng (1980) argued that, for relativistic electrons moving through a
dense gas, the Cerenkov effect will produce peculiar atomic and/or molecular
emission lines–Cerenkov lines. They presented a series of formulae to describe
the new line-mechanism. Elegant experimental confirmation has been obtained by
Xu. et al. in the laboratory which definitely verified the existence of
Cerenkov lines. Owing to the potential importance in high energy astrophysics,
in this paper we give a more detailed physical discussion of the emission
mechanisms and improve the previous formulae system into a form which is more
convenient for astrophysical application. Specifically, the extended formulae
in this paper can be applied to other species of atoms and/or ions rather than
hydrogen as in the previous paper, and also to X-ray astronomy. They can also
be used for the calculation of a nonuniform plane-parallel slab of the emissive
gas.
(58kb)

astro-ph/0009104 [abs, src, ps, other] :

Title: Discovery of 172-s Pulsations from a Be/X-ray Binary Candidate AX
J0051.6-7311 in the SMC with ASCA

Authors:
Jun Yokogawa (1),
Ken’ichi Torii (2),
Kensuke Imanishi (1),
Katsuji Koyama (1) ((1) Kyoto University, (2) National Space Development Agency of Japan)

Comments: 4 pages, 4 figures, to be published in PASJ. Also available at
this http URL

The results from three ASCA observations of AX J0051.6-7311 = RX J0051.9-7311
are reported. Coherent pulsations with a barycentric period of 172.40 +/- 0.03
s were discovered in the third observation, with an exceptionally long exposure
time of ~177 ks. The X-ray spectrum was found to remain unchanged through these
observations, with a photon index of ~0.9. Energy-resolved pulse profiles in
the third observation reveal that the pulsations are mostly due to photons with
an energy above ~2 keV. Archival data of ROSAT and Einstein indicate that AX
J0051.6-7311 exhibits a flux variation having a factor ~> 20.
(70kb)

astro-ph/0009105 [abs, src, ps, other] :

Title: Accretion Disk Instabilities, CDM models and their role in Quasar
Evolution

Authors:
E. Hatziminaoglou (Laboratoire d’Astrophysique de Toulouse),
A. Siemiginowska,
M. Elvis (Harvard – CfA)

Comments: 15 pages, 18 figures, Accepted for Publication in ApJ

We have developed a consistent analytical model to describe the observed
evolution of the quasar luminosity function. Our model combines black hole mass
distributions based on the Press – Schechter theory of the structure formation
in the Universe with quasar luminosity functions resulting from a physics-based
emission model that takes into account the time-dependent phenomena occurring
in the accretion disks. Quasar evolution and CDM models are mutually
constraining, therefore our model gives an estimation of the exponent, n, of
the power spectrum, P(k), which is found to be -1.8 < n < -1.6. We were able to
reject a generally assumed hypothesis of a constant ratio between Dark Matter
Halo and the Black Hole mass, since the observed data could not be fitted under
this assumption. We found that the relation between the Dark Matter Halos and
Black Hole masses is better described by M_{BH}=M_{DMH}^{0.668}. This model
provides a reasonable fit to the observed quasar luminosity function at
redshifts higher than ~2.0. We suggest that the disagreement at lower redshift
is due to mergers. Based on the agreement at high redshift, we estimated the
merger rate at lower redshift, and argue that this rate should depend on the
redshift, like (1+z)^3.
(54kb)

astro-ph/0009106 [abs, src, ps, other] :

Title: Atmospheric Secondary Particles In Near Earth Space

Authors:
Ming-Huey A. Huang (Institute of Physics, Academia Sinica, Taipei, Taiwan)

Comments: 6 pages, 5 figures; Submit to the 8th Asia Pacific Physics Conference

The Alpha Magnetic Spectrometer detects a large amount of particles below
rigidity cutoff. Those high energy particles create questions related to
radiation belts and atmospheric neutrinos. To understand the origin of these
particles, we use a trajectory tracing program to simulate particle
trajectories in realistic geomagnetic field. The complex behaviors and large
e^+/e^- are explained here.
(70kb)

astro-ph/0009107 [abs, src, ps, other] :

Title: On ionisation effects and abundance ratios in damped Lyman-alpha systems

Author:
Daniel Schaerer (OMP, Toulouse),
Yuri Izotov (Main Astronomical Observatory, Kiev),
Corinne Charbonnel (OMP, Toulouse)

Comments: to appear in “Evolution of Galaxies. I. Observational clues”, Eds.
J.M. Vilchez, G. Stasinska, Astrophysics and Space Science, in press. 5
pages, including 3 figures

The similarity between observed velocity structures of Al III and singly
ionised species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionised gas in the regions where most metal absorption lines are formed.

To explore the possible implications of ionisation effects we construct a
simplified two-region model for DLAs consisting of an ionisation bounded region
with an internal radiation field and a neutral region with a lower metal
content. Within this framework we find that ionisation effects are important.
If taken into account, the element abundance ratios in DLAs are quite
consistent with those observed in Milky Way stars and in metal-poor H II
regions in blue compact dwarf galaxies. In particular we cannot exclude the
same primary N origin in both DLAs and metal-poor galaxies. From our models no
dust depletion of heavy elements needs to be invoked; little depletion is
however not excluded.
(50kb)

astro-ph/0009108 [abs, src, ps, other] :

Title: Aberration of Light and Motion of Real Particle

Authors:
Jozef Klacka

Correct and complete (to terms of $vec{v} / c$ — $vec{v}$ is particle’s
velocity, $c$ is the speed of light) derivation of equation of motion for real
dust particle under the action of electromagnetic radiation is derived. The
effect of aberration of light is used. Equation of motion is expressed in terms
of particle’s optical properties, standardly used in optics for stationary
particles.
(4kb)

astro-ph/0009109 [abs, src, ps, other] :

Title: Solar Radiation and Asteroidal Motion

Authors:
Jozef Klacka

Effects of solar wind and solar electromagnetic radiation on motion of
asteroids are discussed. The results complete the statements presented in
Vokrouhlick'{y} and Milani (2000). As for the effect of electromagnetic
radiation, the complete equation of motion is presented to the first order in
$v/c$ — the shape of asteroid (spherical body is explicitly presented) and
surface distribution of albedo should be taken into account. Optical quantities
must be calculated in proper frame of reference.
(4kb)

astro-ph/0009110 [abs, src, ps, other] :

Title: X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 – the
Final ROSAT Observations

Authors:
Werner Becker,
Joachim Tr”umper,
Andrea N.Lommen,
Donald C.Backer

Comments: Accepted for publication in ApJ

We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451.
The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC.
X-ray pulses are detected on a $4.5sigma$ level and make the source the
$11^{th}$ millisecond pulsar detected in the X-ray domain. The pulsed fraction
is found to be $69pm18%$. The X-ray pulse profile is characterized by two
narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming
a Crab-like spectrum the X-ray flux is in the range $f_x= 2-3 imes 10^{-13}$
erg s$^{-1}$ cm$^{-2} $ ($0.1-2.4$ keV), implying an X-ray efficiency of
$L_x/dot{E}sim 0.5-5 imes 10^{-3} (d/0.23 {kpc})^2$.
(286kb)

astro-ph/0009111 [abs, src, ps, other] :

Title: Morphological Number Counts and Redshift Distributions to I = 25 from
the Hubble Deep Fields: Constraints on Cosmological Models from Early Type
Galaxies

Authors:
S. Phillipps,
S.P. Driver,
W.J. Couch,
A. Fernandez-Soto,
P.D. Bristow,
S.C. Odewahn,
R.A. Windhorst,
K. Lanzetta

Comments: Accepted for publication in MNRAS

We combine magnitude and photometric redshift data on galaxies in the Hubble
Deep Fields with morphological classifications in order to separate out the
distributions for early type galaxies. The updated morphological galaxy number
counts down to I = 25 and the corresponding redshift distributions are used as
joint constraints on cosmological models, in particular on the values of the
density parameter Omega_{0} and normalised cosmological constant Lambda_{0}.

We find that an Einstein – de Sitter universe with simple passive evolution
gives an excellent fit to the counts and redshift data at all magnitudes. An
open, low Omega_{0}, model with no net evolution (and conservation of the
number of ellipticals), which fits the counts equally well, is somewhat less
successful, predicting slightly lower mean redshifts and, more significantly,
the lack of a high–z tail. A number conserving model with a dominant
contribution from Lambda_{0}, on the other hand, is far less successful,
predicting a much narrower distribution than seen. More complex models are
obviously possible, but we conclude that if large scale transmutation between
types does {it not} occur, then the lambda-dominated models provide a very
poor fit to the current data.
(35kb)

astro-ph/0009112 [abs, src, ps, other] :

Title: HI in Early-Type Galaxies

Authors:
T. Oosterloo (NFRA),
R. Morganti (NFRA),
E.M. Sadler (Sydney)

Comments: To appear in the proceedings of the conference “Gas and Galaxy
Evolution” (ASP Conference Series), eds. J. Hibbard, M. Rupen, and J. van
Gorkom

We briefly discuss the main differences between the HI properties of luminous
and low-luminosity early-type galaxies. In luminous early-type galaxies the HI
is often irregularly distributed, but in a few cases regular HI disks, of low
surface density, are seen. In low-luminosity galaxies, the HI is more often in
a disk with high central surface densities. This suggests a different evolution
of the gas in these two groups of galaxies.
(87kb)

astro-ph/0009113 [abs, src, ps, other] :

Title: Antikaon condensation and the metastability of protoneutron stars

Authors:
Sarmistha Banik,
Debades Bandyopadhyay

Comments: 26 pages; Revtex; 8 figures included

We investigate the condensation of $ar K^0$ meson along with $K^-$
condensation in the neutrino trapped matter with and without hyperons.
Calculations are performed in the relativistic mean field models in which both
the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson
exchange. In the neutrino trapped matter relevant to protoneutron stars, the
critical density of $K^-$ condensation is shifted considerably to higher
density whereas that of $ar K^0$ condensation is shifted slightly to higher
density with respect to that of the neutrino free case. The onset of $K^-$
condensation always occurs earlier than that of $ar K^0$ condensation. A
significant region of maximum mass protoneutron stars is found to contain $ar
K^0$ condensate for larger values of the antikaon potential. With the
appearance of $ar K^0$ condensation, there is a region of symmetric nuclear
matter in the inner core of a protoneutron star. It is found that the maximum
mass of a protoneutron star containing $K^-$ and $ar K^0$ condensate is
greater than that of the corresponding neutron star. We revisit the implication
of this scenario in the context of the metastability of protoneutron stars and
their evolution to low mass black holes.
(122kb)

astro-ph/0009114 [abs, src, ps, other] :

Title: Asphericity of galaxy clusters and Sunyaev-Zel’dovich effect

Authors:
D. Puy,
L. Grenacher,
Ph. Jetzer (PSI and Institute of Theoretical Physics-Univ. Zurich),
M. Signore (Obs. Paris)

Comments: 20 pages, 9 figures. accepted for publication in Astronomy and
Astrophysics

In this paper we investigate the Sunyaev-Zel’dovich (SZ) effect and the X-ray
surface brightness for clusters of galaxies with a non-spherical mass
distribution. In particular, we consider the influence of the shape and the
finite extension of a cluster as well as of a polytropic thermal profile on the
Compton parameter, the X-ray surface brightness and on the determination of the
Hubble constant. We find that the non-inclusion of such effects can induce
errors up to 30% in the various parameters and in particular on the Hubble
constant value, when compared with results obtained under the isothermal,
infinitely extended and spherical shape assumptions.
(53kb)

astro-ph/0009115 [abs, src, ps, other] :

Title: The HI halo of NGC 2403

Authors:
Filippo Fraternali (IRA and Bologna Univ.),
Tom Oosterloo (NFRA),
Renzo Sancisi (AOB and Kapteyn Inst.),
Gustaaf van Moorsel (NRAO)

Comments: 2 pages, 2 ps figures; to appear in “Gas & Galaxy Evolution”, VLA
20th Anniversary Conference, J.E. Hibbard, M.P. Rupen & J.H. van Gorkom
(eds.)

Deep VLA HI observations of the nearby spiral galaxy NGC 2403 reveal the
presence of an extended HI halo that shows slower rotation and a general inflow
(about 15-25 kms) towards the center of the galaxy.
(210kb)

astro-ph/0009116 [abs, src, ps, other] :

Title: Parsec-scale structures of radio galaxies in the 2-Jy sample

Authors:
Venturi T.,
Morganti R.,
Tzioumis T.,
Reynolds J

Comments: 10 pages, 10 figures, A&A in press

In this paper we present the results of VLBI observations of six radio
galaxies belonging to the 2-Jy sample. The selected objects are 3C17, PKS
0620-52, PKS 0625-35, PKS 1318-43, PKS 1333-33 and 3C317. The first is a high
power radio galaxy and the remainder are low power objects. Our observations
were carried out with a set of different arrays and frequencies, and cover a
range of resolutions from a few mas to a few tens of mas. Parsec-scale images
are presented and discussed in the light of unification for radio loud
galaxies. Estimates for the intrinsic plasma speed in these objects in the
proximity of the parsec-scale core and tehir orientation to the line of sight
are in agreement with the predictions from unified models and their optical and
X-ray properties.
(89kb)

astro-ph/0009117 [abs, src, ps, other] :

Title: Multiband optical polarimetry of the BL Lac object PKS 2155–304.
Intranight and long term variability

Authors:
Leonardo Tommasi (Universita’ di Milano),
Ruben Diaz (Observatorio Astronomico de Cordoba),
Eliana Palazzi (ITESRE-CNR, Bologna),
Elena Pian (ITESRE-CNR, Bologna),
Ennio Poretti (Osservatorio Astronomico di Brera),
Franco Scaltriti (Osservatorio Astronomico di Torino),
Aldo Treves (Universita’ dell’Insubria)

Comments: 21 pages, 6 eps figures. Accepted for The Astrophysical Journal
Supplement Series

The polarized and total flux of the BL Lac object PKS 2155-304 were monitored
intensively and simultaneously in the optical UBVRI bands with the Turin
photopolarimeter at the CASLEO 2.15 m telescope during 4 campaigns in June,
August, November 1998 and August 1999. The effective observation time amounted
to ~47 hours. PKS 2155-304 showed a linear polarization percentage (P) usually
ranging between 3% and 7% and a polarization position angle (PA) mainly between
70 and 120 deg. The highest temporal resolution of our observations, 15
minutes, is unprecedented for polarimetric monitoring of this source, and has
allowed us to detect amplitude variations of the linear polarization percentage
from 6 to 7.5% in time scales of hours. In some nights the polarization
percentage seems to increase toward shorter wavelengths, however the polarized
spectrum does not vary significantly with time. The most remarkable variability
event occurred on 1998 June 18, when the degree of linear polarization
decreased by more than a factor 2 in one day in all bands, while the PA rotated
by 90 deg. This is consistent with the presence of two emission components, of
different polarization degree and position angle. Intranight variability of P
and PA can be interpreted with small amplitude physical or geometrical changes
within the jet. Measurements of the circular polarization over time intervals
of days set upper limits of 0.2%. Simultaneous photometry taken with the Turin
Photopolarimeter and with a CCD camera at Cordoba Astronomical Observatory did
not show light variations correlated with those of the linearly polarized flux.
(73kb)

astro-ph/0009118 [abs, src, ps, other] :

Title: 2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2
Molecular Clouds

Authors:
John M. Carpenter (Caltech)

Comments: to appear in AJ, December 2000; see also
this http URL

We use the 2MASS Second Incremental Release Point Source Catalog to
investigate the spatial distribution of young stars in the Perseus, Orion A,
Orion B, and MonR2 molecular clouds. After subtracting a semi-empirical model
of the field star contamination from the observed star counts, stellar surface
density maps are used to identify compact clusters and any stellar population
found more uniformly distributed over the molecular cloud. Each cloud contains
between 2 to 7 clusters, with at least half of the cluster population found in
a single, rich cluster. In addition, a distributed stellar population is
inferred in the Orion A and MonR2 molecular clouds within the uncertainties of
the field star subtraction with a surface density between 0.013 – 0.083
arcmin**-2. The fraction of the total stellar population contained in clusters
for the nominal extinction model ranges from ~50-100% if the distributed
population is relatively young (< 10 Myr), to ~25%-70% if it is relatively old
(~100 Myr). The relatively high fraction of stars contained in clusters
regardless of the age of the distributed population, in conjunction with the
young ages generally inferred for embedded clusters in nearby molecular clouds,
indicates that a substantial fraction of the total stellar population in these
regions has formed within the past few million years in dense clusters. This
suggests that either the star formation rate in each these clouds has recently
peaked if one assumes clouds have ages > 10 Myr, or molecular clouds are
younger than typically thought if one assumes that the star formation rate has
been approximately constant in time.
(319kb)

astro-ph/0009119 [abs, src, ps, other] :

Title: The HI halos of spiral galaxies

Authors:
Renzo Sancisi (AOB and Kapteyn Inst.),
Filippo Fraternali (IRA and Bologna Univ.),
Tom Oosterloo (NFRA),
Gustaaf van Moorsel (NRAO)

Comments: 8 pages, 4 ps figures; to appear in “Gas & Galaxy Evolution”, VLA
20th Anniversary Conference, J.E. Hibbard, M.P. Rupen & J.H. van Gorkom
(eds.)

The results of observational studies on the vertical HI density distribution
and kinematics of the disks of spiral galaxies are reported and discussed.
Attention is drawn to the presence of HI emission, unknown before and here
referred to as the `beard’, which has anomalous structure and kinematics,
different from the known cold HI disk. This component is extended and probably
located in the halo region, it is rotating more slowly than the disk and shows
radial inward motion. Its nature and origin -galactic fountain or infall of
primordial gas?- are still a puzzle.
(368kb)

astro-ph/0009120 [abs, src, ps, other] :

Title: Cooling of Hybrid Neutron Stars and Hypothetical Self-bound Objects with
Superconducting Quark Cores

Authors:
D. Blaschke,
H. Grigorian,
D.N. Voskresensky

Comments: 8 pages, 4 figures, uses aa.cls

We study the consequences of superconducting quark cores (with
color-flavor-locked phase as representative example) for evolution of
temperature profiles and the cooling curves in quark-hadron hybrid stars and in
hypothetical self-bounded objects having no a hadron shell (quark core neutron
stars). The quark gaps are varied from 0 to $Delta_q =50$ MeV. For hybrid
stars we find time scales of $1div5$, $5div10$ and $50div100$ years for the
formation of a quasistationary temperature distribution in the cases $Delta_q
=0$, 0.1 MeV and $gsim$ 1 MeV, respectively. These time scales are governed by
the heat transport within quark cores for large diquark gaps ($Delta gsim$ 1
MeV) and within the hadron shell for small diquark gaps ($Delta lsim 0.1$
MeV). For quark core neutron stars we find a time scale $simeq 300$ years for
the formation of a quasistationary temperature distribution in the case $Delta
gsim$ 10 MeV and a very short one for $Delta lsim$ 1 MeV. If hot young
compact objects will be observed they can be interpreted as manifestation of
large gap color superconductivity. Depending on the size of the pairing gaps,
the compact star takes different paths in the ${lg}T_s $ vs. ${lg} t$ diagram
where $T_s$ is the surface temperature. Compared to the corresponding hadronic
model which well fits existing data the model for the hybrid neutron star (with
a large diquark gap) shows too fast cooling. The same conclusion can be drawn
for the corresponding self-bound objects.
(59kb)

astro-ph/0009121 [abs, src, ps, other] :

Title: High-Redshift Galaxies: The Far-Infrared and Sub-Millimeter View

Authors:
Alberto Franceschini

Comments: Comments: 60 pages, Latex with special macro. To appear in the
Proceedings of the XI Canary Islands Winter School Of Astrophy+ on “Galaxies
at High Redshift”, Tenerife November 1999, F. Sanchez, I. Perez-Fournon, M.
Balcells, F. Moreno-Insertis Eds., Cambridge University Press

Observations at long wavelengths, in the wide interval from a few to 1000
micron, are essential to study diffuse media in galaxies, including all kinds
of atomic, ionic and molecular gases and dust grains. Hence they are
particularly suited to investigate the early phases in galaxy evolution, when a
very rich ISM is present in the forming systems.

During the last few years a variety of observational campaigns in the
far-IR/sub-mm, exploiting both ground-based and space instrumentation, have
started to provide results of relevant cosmological impact. Most crucial among
these have been the discovery of an intense diffuse background in the
far-IR/sub-mm of extragalactic origin, and the deep explorations from space in
the far-IR and with large millimetric telescopes on ground. These results
challenge those obtained from optical-UV observations, by revealing luminous to
very luminous phases in galaxy evolution at substantial redshifts, likely
corresponding to violent events of star-formation in massive systems. This is
bringing to significant refinements of the present schemes of galaxy formation,
as far as the history of baryon transformations is concerned.
(344kb)

astro-ph/0009122 [abs, src, ps, other] :

Title: The Magnetic Field Geometry in M82 and Cen A

Authors:
Terry Jay Jones

Imaging polarimetry at 1.65 and 2.2 $mu $m is presented for the classic
starburst galaxy M82 and the advanced merger system Cen A. Polarimetry at near
IR wavelengths allows the magnetic field geometry in galaxies to be probed much
deeper into dusty regions than optical polarimetry. In M82, the magnetic field
throughout the nucleus has a polar geometry, presumably due to the massive
vertical flow that is a result of the intense star formation there. Fully two
thirds of the line of sight dust through to the center of M82 contains a
vertical magnetic field. In Cen A, the prominent dust lane shows a normal
planar field geometry. There is no indication of significant disturbance in the
field geometry in the dust lane and the polarization strength is near normal
for the amount of extinction. Either the magnetic field geometry was well
maintained during the merger, or it reestablished itself very easily.
(289kb)

astro-ph/0009123 [abs, src, ps, other] :

Title: Discovery of An Extremely Metal–Poor Galaxy: Optical Spectroscopy of
UGCA 292

Authors:
L. van Zee (HIA)

Comments: 4 pages, 2 figures, uses emulateapj5, accepted by ApJL

The results of optical spectroscopy of two HII regions in UGCA 292 (CVn I
dwA) are presented. UGCA 292 is a nearby (D=3.1 Mpc) gas-rich dwarf irregular
galaxy (M_H/L_B ~ 6.9) which was first discovered in a blind HI survey. The
derived oxygen abundance is the third lowest of known star-forming galaxies [12
+ log(O/H) = 7.30 +/- 0.05], making UGCA 292 one of the nearest metal-poor
galaxies known. The derived N/O ratio is similar to that found in other low
metallicity galaxies [log(N/O) = -1.47 +/- 0.10], and is indicative of a
primary origin for nitrogen. The derived oxygen abundance is consistent with
closed-box chemical evolution for this low mass galaxy. The observed blue
colors, high gas mass fraction, and low metallicity suggest that UGCA 292 is
relatively unevolved. The possibility that future blind HI surveys may yield
similar low metallicity galaxies is discussed.
(48kb)

astro-ph/0009124 [abs, src, ps, other] :

Title: VLBA Observations Of A Sample Of Nearby FR I Radio Galaxies

Authors:
Chun Xu,
Stefi A. Baum,
Christopher P. O’Dea,
J.M. Wrobel,
J.J. Condon

Comments: 32 pages, 7 figures

We observed 17 nearby low luminosity FR I radio galaxies using the NRAO Very
Long Baseline Array (VLBA) at 1.67 GHz, as part of a multi-wavelength study of
a complete sample of 21 sources selected by radio flux density from the Uppsala
General Catalogue of Galaxies. We detected radio emission from all 17 galaxies.
At a FWHM resolution of ~ 10×4 mas, five galaxies show only an unresolved radio
core, ten galaxies show core-jet structures, and two galaxies show twin-jet
structures. Comparing these VLBA images with images previously obtained with
the NRAO VLA, we find that all detected VLBA jets are well-aligned on parsec
scales with the VLA jets on kilo parsec scales, and that the jet to counter-jet
surface brightness ratios, or the sidedness, decreases systematically with
increasing distance along the jet. We attribute the sidedness to the Doppler
boosting effect and its decline to the deceleration of the jets. We show that a
distribution of Lorentz factor centered near Gamma = 5 can reproduce our VLBA
detection statistics for core, core-jet and twin-jet sources. We also note that
the luminosity per unit length, L_j, of the VLBA jets drops quickly with
distance, r, along the jet, approximately as L_j being proportional to
r^(-2.0). We discuss three different mechanisms to explain this jet fading: (1)
the decrease of Doppler boosting due to jet deceleration, (2) synchrotron
losses, and (3) expansion losses in constant velocity but adiabatically
spreading jets. Mechanisms (1) and (2) are inconsistent with the observations,
while mechanism (3) is consistent with the observations provided the magnetic
field lines in the jets are aligned perpendicular to the jet axis. This implies
that the deceleration of the jets required by the Unified Scheme does not occur
on the tens of parsec scales, but must occur on larger scales.
(257kb)

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Cross-listings

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hep-ph/0009065 [abs, src, ps, other] :

Title: Neutralino Dark Matter Elastic Scattering in a Flat and Accelerating
Universe

Authors:
A.B. Lahanas,
D.V. Nanopoulos,
V.C. Spanos

Comments: 15 pages, 9 figures included using epsfig style

In SUGRA inspired supersymmetric models with universal boundary conditions
for the soft masses, the scalar cross section $sigma_{scalar}$ for the elastic
neutralino–nucleon scattering is in general several orders of magnitude below
the sensitivity of current experiments. For large $ an eta$ and low
$M_{1/2}, m_0$ values, the theoretically predicted $sigma_{scalar}$ can
approach the sensitivity of these experiments ($approx 10^{-6} pb$) being at
the same time in agreement with recent cosmological data, which impose severe
restrictions on the CDM relic density, and with accelerator experiments which
put lower bounds on sparticle and Higgs boson masses. Further improvement of
the sensitivity of DAMA and CDMS experiments will probe the large $ an eta$
region of the parameter space in the vicinity of the boundaries of the
parameter space allowed by chargino and Higgs searches.
(372kb)

hep-ph/0009075 [abs, src, ps, other] :

Title: Boltzmann Suppression of Interacting Heavy Particles

Authors:
Patrizia Bucci,
Massimo Pietroni

Comments: 7 pages, 5 figures

Matsumoto and Yoshimura have recently argued that the number density of heavy
particles in a thermal bath is not necessarily Boltzmann-suppressed for T << M,
as power law corrections may emerge at higher orders in perturbation theory.
This fact might have important implications on the determination of WIMP relic
densities. On the other hand, the definition of number densities in a
interacting theory is not a straightforward procedure. It usually requires
renormalization of composite operators and operator mixing, which obscure the
physical interpretation of the computed thermal average. We propose a new
definition for the thermal average of a composite operator, which does not
require any new renormalization counterterm and is thus free from such
ambiguities. Applying this definition to the model of Matsumoto and Yoshimura
we find that it gives number densities which are Boltzmann-suppressed at any
order in perturbation theory.
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astro-ph/0009081 [abs, src, ps, other] :

Title: Ionized Gas in Damped Lyman Alpha Protogalaxies: I. Model-Independent
Inferences From Kinematic Data

Authors:
Arthur M. Wolfe (University of California, San Diego),
Jason X. Prochaska (The Observatories of the Carnegie Institute of Washington)

Comments: 15 pages, 9 figures, Accepted for publication in Dec. 20 issue of the
Astrophysical Journal

Note: replaced with revised version Thu, 7 Sep 2000 22:08:29 GMT (206kb)

astro-ph/0009082 [abs, src, ps, other] :

Title: Ionized Gas in Damped Lyman Alpha Protogalaxies: II. Comparison Between
Models and the Kinematic Data

Authors:
Arthur M. Wolfe (University of California, San Diego),
Jason X. Prochaska (The Observatories of the Carnegie Institute of Washington)

Comments: 18 pages, 12 Figures, Accepted for publication in the Dec. 20 issue
of the Astrophysical Journal

Note: replaced with revised version Thu, 7 Sep 2000 22:15:54 GMT (143kb)

astro-ph/0009093 [abs, src, ps, other] :

Title: Medium Effects in Neutrino Cooling of Neutron Stars

Authors:
D.N. Voskresensky

Comments: Invited talk at Intern. Workshop on Phys. of Neutron Star Interiors,
Trento, June 2000; 30 pages

Note: replaced with revised version Thu, 7 Sep 2000 15:12:17 GMT (182kb)

gr-qc/0006058 [abs, src, ps, other] :

Title: Black holes and a scalar field in expanding universe

Authors:
Hiromi Saida,
Jiro Soda

Comments: 14 pages, 2 tables, 5 figures

Note: replaced with revised version Thu, 7 Sep 2000 04:36:00 GMT (30kb)

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Title: Recent Seminal Results

Authors: Author One and Author Two

Comments: 3 pages, latex, no figures, mpeg simulations available at

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Report-no: EFI-2000-28

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