Astrophysics

astro-ph new abstracts, Fri, 18 Aug 00 04:00:15 GMT
0008255 — 0008281 received

astro-ph/0008255 [abs, src, ps, other] :

Title: Search for High Energy Neutrino Emission from Gamma-Ray Bursts with the
A ntarctic Muon and Neutrino Detector Array (AMANDA)
Authors:
Ryan C. Bay
Comments: Ph.D. thesis (64 pages)

The photo-meson production of pions by shock-accelerated protons could
generate a burst of ~10^14 eV neutrinos from gamma-ray bursts (GRBs) observable
in the Antarctic Muon and Neutrino Detector Array (AMANDA) or its larger
successors. Measurement of this flux can test the hypothesis that GRBs are the
sources of the highest-energy cosmic rays, and GRB neutrinos could permit
high-precision experiments in neutrino limiting speed, neutrino oscillations,
and the weak equivalence principle. Neutrino emission can be expected primarily
during the prompt gamma-ray flash and satellite coincidence provides a
well-defined window in position and time that can be searched for an excess of
upgoing muon events in AMANDA from bursts in the Northern Hemisphere. Using an
event quality analysis to further reduce background in a sample of 78 GRBs from
the 1997 AMANDA-B10 data set, I find a fluence limit of (E_nu)^2
(dN_nu)/(dE_nu)<3.8*10^-4 min(1,E_nu/E_break) [TeV cm^-2] per average burst,
which is orders of magnitude more stringent than in similar previous searches.
(204kb)

astro-ph/0008256 [abs, src, ps, other] :

Title: The 1997 periastron passage of the binary pulsar PSR B1259-63
Authors:
Simon Johnston,
N. Wex,
L. Nicastro,
R. N. Manchester,
A.G. Lyne
Comments: 5 pages, 4 figures. Submitted to the black hole at MNRAS

We report here on multifrequency radio observations of the pulsed emission
from PSR B1259-63 around the time of the closest approach to its B2e companion
star. There was a general increase in the pulsar’s dispersion measure and
scatter broadening, and a decrease in the flux density towards periastron
although changes in these parameters were seen on timescales as short as
minutes. The pulsed emission disappeared 16 days prior to periastron and
remained undetectable until 16 days after periastron.

The observations are used to determine the parameters of the wind from the Be
star. We show that a simple model, in which the wind density varies with radius
as r^-2, provides a good fit to the data. The wind is clumpy with size scales
<= 10^10 cm, densities of 10^6 cm^-3 and a velocity of 2000 km/s at a distance
of 20 – 50 stellar radii. We find a correlation between dispersion measure
variations and the pulse scattering times, suggesting that the same electrons
are responsible for both effects.
(29kb)

astro-ph/0008257 [abs, src, ps, other] :

Title: HI line measurements of pulsars towards the Galactic Centre and the
electron density in the inner Galaxy
Authors:
Simon Johnston,
B. Koribalski,
J. M. Weisberg,
W. Wilson
Comments: 9 pages, 8 figures. Submitted to MNRAS

We have measured 21-cm absorption and emission spectra in the direction of a
further 7 southern pulsars with the Parkes telescope to derive their kinematic
distances and to study the interstellar medium. For the first time we have
successfully obtained HI absorption measurements for PSRs J1602-5100,
J1740-3015 and J1745-3040. We have also significantly improved the sensitivity
and resolution on PSRs J1600-5044, J1752-2806, and J1825-0935, whose spectra
have previously been measured, and have corrected an error in the published
distance to PSR J1824-1945.

Since the Frail & Weisberg summary of pulsar distances in 1990, a further 23
pulsars now have measured HI distances, mainly through the efforts of the
current group. We discuss the Taylor & Cordes electron density model in light
of these new measurements and find that, although the model towards the
Galactic Centre appears good, the line of sight through the Carina spiral arm
is poorly fit by the model.
(61kb)

astro-ph/0008258 [abs, src, ps, other] :

Title: QSO 2359-1241: A Bright, Highly Polarized, Radio-Moderate, Reddened,
Low-Ionization Broad Absorption Line Quasar
Authors:
M. S. Brotherton,
Nahum Arav,
R. H. Becker,
Hien D. Tran,
Michael D. Gregg,
R. L.. White,
S. A. Laurent-Muehleisen,
Warren Hack
Comments: To appear in ApJ. See also companion paper by Arav et al

We report the discovery of a bright quasar (E=15.8, z=0.868) associated with
the flat spectrum radio source NVSS J235953-124148. This quasar we designate
QSO 2359-1241 possesses a rare combination of extreme properties that make it
of special interest. These properties include: intrinsic high-velocity outflow
seen in absorption for both high and low-ionization species, high optical
polarization (about 5%), significant radio emission, and dust reddening. The
dereddened absolute magnitude of QSO 2359-1241 places it among the three most
optically luminous quasars known at z<1. High-resolution spectroscopy and a
detailed analysis of the optical/ultraviolet absorption features will be given
in a companion paper (Arav et al 2000).
(493kb)

astro-ph/0008259 [abs, src, ps, other] :

Title: The Intrinsic Absorber in QSO 2359-1241: Keck and HST Observations
Authors:
Nahum Arav,
Michael S. Brotherton,
Robert H. Becker,
Michael D. Gregg,
Richard L. White,
Trevor Price,
Warren Hack
Comments: 30 pages, 9 figures, in press with the ApJ

We present detailed analyses of the absorption spectrum seen in QSO 2359-1241
(NVSS J235953-124148). Keck HIRES data reveal absorption from twenty
transitions arising from: He I, Mg I, Mg II, Ca II, and Fe II. HST data show
broad absorption lines (BALs) from Al III 1857, C IV 1549, Si IV 1397, and N V
1240. Absorption from excited Fe II states constrains the temperature of the
absorber to 2000K < T < 10,000K and puts a lower limit of 10^5 cm^{-3} on the
electron number density. Saturation diagnostics show that the real column
densities of He I and Fe II can be determined, allowing to derive meaningful
constraints on the ionization equilibrium and abundances in the flow. The
ionization parameter is constrained by the iron, helium and magnesium data to
-3.0 < log(U) < -2.5 and the observed column densities can be reproduced
without assuming departure from solar abundances. From comparison of the He I
and Fe II absorption features we infer that the outflow seen in QSO 2359-1241
is not shielded by a hydrogen ionization front and therefore that the existence
of low-ionization species in the outflow (e.g., Mg II, Al III, Fe II) does not
necessitate the existence of such a front. We find that the velocity width of
the absorption systematically increases as a function of ionization and to a
lesser extent with abundance. Complementary analyses of the radio and
polarization properties of the object are discussed in a companion paper
(Brotherton et al. 2000).
(174kb)

astro-ph/0008260 [abs, src, ps, other] :

Title: Black Holes Must Die
Authors:
Neal Dalal,
Kim Griest

In light of recent evidence suggesting a nonzero present-day cosmological
constant, Adams, Mbonye, & Laughlin (1999) have considered the evolution of
black holes in the presence of vacuum energy. Using the assumption that Lambda
remains constant with time, and a conjecture based on a paper by Mallett
(1986), they reach the remarkable conclusion that black holes with current mass
greater than about 2*10^(-9) Msun will not Hawking evaporate in the distant
future, but will instead absorb vacuum energy and grow to roughly the de Sitter
horizon size. In this letter we reexamine black hole evaporation in the
presence of vacuum energy, and find instead that all known black holes will
eventually evaporate.
(6kb)

astro-ph/0008261 [abs, src, ps, other] :

Title: Polarized mm And sub-mm Emission From Sgr A* At The Galactic Center
Authors:
Fulvio Melia,
Siming Liu,
Robert Coker
Comments: 12 pages, 4 figures. Submitted to APJL

The recent detection of significant linear polarization at mm and sub-mm
wavelengths in the spectrum of Sgr A* (if confirmed) will be a useful probe of
the conditions within several Schwarzschild radii ($r_S$) of the event horizon
at the Galactic Center. Hydrodynamic simulations of gas flowing in the vicinity
of this object suggest that the infalling gas circularizes when it approaches
within $5-25 r_S$ of the black hole. We suggest that the sub-mm “excess” of
emission seen in the spectrum of Sgr A* may be associated with radiation
produced within the inner Keplerian region and that the observed polarization
(16kb)

astro-ph/0008262 [abs, src, ps, other] :

Title: Effects of dust extinction on optical spectroscopic properties for
starburst galaxies in distant clusters
Author:
Yasuhiro Shioya,
Kenji Bekki
Comments: 14 pages 3 figures (1 color), ApJL in press

Recent observational studies on galaxies in distant clusters discovered a
significant fraction of possible dusty starburst galaxies with the so-called
`e(a)’ spectra that are characterized by strong H$delta$ absorption and
relatively modest [OII] emission. We numerically investigate spectroscopic and
photometric evolution of dusty starburst galaxies in order to clarify the
origin of the e(a) spectra. We found that if a young starburst population is
preferentially obscured by dust than an old one in a dusty starburst galaxy,
the galaxy shows e(a) spectrum. It is therefore confirmed that the selective
dust extinction, which is first suggested by Poggianti & Wu (2000) and means
the strongest dust extinction for the youngest stellar population among stellar
populations with different ages, is critically important to reproduce
quantitatively the observed e(a) spectra for the first time in the present
numerical study. We furthermore discuss what physical process is closely
associated with this selective dust extinction in cluster environment.
(30kb)

astro-ph/0008263 [abs, src, ps, other] :

Title: Distance Constraints for High Velocity Clouds from Optical Emission
Lines
Authors:
Benjamin J. Weiner (OCIW),
Stuart N. Vogel (Maryland),
T.B. Williams (Rutgers)
Comments: To appear in proceedings of Gas and Galaxy Evolution, (VLA 20th
Anniversary Conference), ASP Conf. Series, ed. J. Hibbard, M. Rupen, & J. van
Gorkom. 6 pages, 3 figures, uses newpasp.sty

We report results from a survey of high velocity clouds and the Magellanic
Stream for faint, diffuse optical recombination emission lines. We detect
H-alpha emission with surface brightness from 41 to 1680 milli-Rayleighs (mR)
from HVCs, and from <40 to 1360 mR in the MS. A simple model for the
photoionizing radiation emergent from the Galaxy, normalized to the HVCs A and
M with known distances, predicts distances from a few to 40 kpc, placing the
faintest HVCs in the Galactic halo, too far away for a Galactic fountain. This
model cannot explain the bright and spatially varying H-alpha in the Magellanic
Stream, which requires another source of ionization. However, we do not find
any HVCs super-faint in H-alpha; even with another ionization source, we
conclude that the detected HVCs are not more than 2–4 times the distance of
the MS (100-200 kpc).
(82kb)

astro-ph/0008264 [abs, src, ps, other] :

Title: A Statistical Study of Emission Lines from High Redshift Radio Galaxies
Authors:
Carlos De Breuck (Leiden and IGPP/LLNL),
Huub Rottgering (Leiden),
George Miley (Leiden),
Wil van Breugel (IGPP/LLNL),
Philip Best (Leiden)
Comments: 28 Pages, including 22 PostScript figures. Accepted for publication
in Astronomy & Astrophysics

We have compiled a sample of 165 radio galaxies from the literature to study
the properties of the extended emission line regions and their interaction with
the radio source over a large range of redshift 0<z<5.2. For each source, we
have collected radio (size, lobe distance ratio and power) and spectroscopic
parameters (luminosity, line width and equivalent width) for the four brightest
UV lines. We also introduce a parameter A_{Ly-alpha} measuring the asymmetry of
the Ly-alpha line. Using these 18 parameters, we examine the statistical
significance of all 153 mutual correlations, and find the following significant
correlations: (i) Ly-alpha asymmetry A_{Ly-alpha} with radio size and redshift,
(ii) line luminosity with radio power, (iii) line luminosities of UV lines with
each other, and (iv) equivalent widths of UV lines with each other. Using
line-ratio diagnostic diagrams, we examine the ionization mechanism of the
extended emission line regions in HzRGs. The high ionization lines seem to
confirm previous results showing that AGN photo-ionization provides the best
fit to the data, but are inconsitent with the CII/CIII ratio, which favour the
highest velocity shock ionization models. We note that the CII line is 5 times
more sensitive to shock ionization than the high ionization UV lines, and show
that a combination of shock and photo-ionization provides a better overall fit
to the integrated spectra of HzRGs. Because most HzRGs have radio sizes <~150
kpc, their integrated spectra might well contain a significant contribution
from shock ionized emission. [abridged]
(149kb)

astro-ph/0008265 [abs, src, ps, other] :

Title: Cosmic concordance and the fine structure constant
Authors:
R.A. Battye,
R. Crittenden,
J. Weller
Comments: 12 Pages

Recent measurements of a peak in the angular power spectrum of the cosmic
microwave background appear to suggest that geometry of the universe is close
to being flat. But if other accepted indicators of cosmological parameters are
also correct then the best fit model is marginally closed, with the peak in the
spectrum at larger scales than in a flat universe. Such observations can be
reconciled with a flat universe if the fine structure constant had a lower
value at earlier times, which would delay the recombination of electrons and
protons and also act to suppress secondary oscillations as observed. We discuss
evidence for a few percent increase in the fine structure constant between the
time of recombination and the present.
(93kb)

astro-ph/0008266 [abs, src, ps, other] :

Title: Using Perturbative Least Action to Reconstruct Redshift Space
Distortions
Authors:
David M. Goldberg (Yale University; Princeton University Observatory)
Comments: 34 Pages LaTeX, including 10 postscript figures. Submitted to
Astrophysical Journal

In this paper, we present a redshift space reconstruction scheme which is
analogous to and extends the Perturbative Least Action (PLA) method described
by Goldberg & Spergel (2000). We first show that this scheme is effective in
reconstructing even nonlinear observations. We then suggest that by varying the
cosmology to minimize the quadrupole moment of a reconstructed density field,
it may be possible to lower the errorbars on the redshift distortion parameter,
$eta$ as well as to break the degeneracy between the linear bias parameter,
$b$, and $Omega_M$. Finally, we discuss how PLA might be applied to realistic
redshift surveys.
(174kb)

astro-ph/0008267 [abs, src, ps, other] :

Title: The Extreme Scattering Event Toward 1741-038: H I Absorption
Authors:
T. J. W. Lazio (1),
R. A. Gaume (2),
M. J. Claussen (3), et al. ((1) NRL, (2) Usno, (3) Nrao)
Comments: 9 pages, LaTeX2e with AASTeX5.0; 4 PostScript figures in 4 files;
accepted for publication in the ApJ, vol. 546, 2001 January 1

We report multi-epoch VLA H I absorption observations of the source 1741-038
(OT-068) before and during an extreme scattering event (ESE). Observations at
four epochs, three during the ESE, were obtained. We find no changes in the
equivalent width, maximum optical depth, or velocity of maximum optical depth
during the ESE, but we do find a secular trend of decreasing maximum optical
depth between our observations and ones by other observers a decade prior. The
resulting limit on the H I column density change during the ESE for a structure
with a spin temperature T_s is 6.4 x 10^{17} cm^{-2} (T_s/10 K). Tiny-scale
atomic structures (TSAS), with a column density N_H ~ 3 x 10^{18} cm^{-2}, are
ruled out marginally by this limit, though geometric arguments may allow this
limit to be relaxed. Galactic halo molecular clouds, that are opaque in the H I
line, cannot be excluded because the observed velocity range covers only 25% of
their allowed velocity range.
(35kb)

astro-ph/0008268 [abs, src, ps, other] :

Title: The Effect of the (2+1)-Dimensional Gravity in the Spiral Galaxy
Authors:
W.F. Kao,
R.-T. Yu
Comments: 3 pages

The slowly decreasing rotational velocity of the Milky Way suggests the
existence of the dark matter. One finds that the effect of the dark matter in a
galaxy can be described by a $(2+1)$-dimensional fluid model. The stability
analysis for the corresponding fluid model is discussed in details in this
paper. It is found that the pressure term plays an important role in the
stability of the spiral arms and counteracts the increasing mass of the
observed galaxy as the radial distance increases. When the fluid region ends,
the $ nearly $ constant rotational velocity of the distant stars require no
additional mass if the spatial dimension in the remote region is close to two.
This indicates that the galaxies, we are interested, could be explained by a
$(2+1)$-dimensional model. Possible implications are also discussed in this
paper.
(5kb)

astro-ph/0008269 [abs, src, ps, other] :

Title: Kinematics and morphology of the Narrow-Line Region in the Seyfert
galaxy NGC1386
Authors:
J. Rossa (1,2),
M. Dietrich (1,3),
S.J. Wagner (1) ((1) Landessternwarte Heidelberg-Koenigstuhl, Germany, (2) Astronomisches Institut der Ruhr-Universitaet Bochum, Germany, (3) Department of Astronomy, University of Florida, Gainesville, USA)
Comments: LaTeX, 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysics

We present a high spatial and spectral resolution 2-D echelle spectrogram of
the Narrow-Line Region in the Seyfert 2 galaxy NGC1386. This Seyfert galaxy was
observed with CASPEC in the wavelength range 5270-7725 Angstrom which covers
the H-alpha and the [N II] lines. With the use of spatially high resolved
images taken with the WFPC2 aboard the Hubble Space Telescope we could identify
individual components of the Narrow-Line Region in our spectra. A Gaussian
decomposition of the spectra revealed 9 distinct emission-line complexes. The
brightest component is blue-shifted by -120+-10 km/s with respect to the
systemic velocity and shows an offset of -1.6″ relative to the nucleus of the
galaxy. The true nucleus of NGC1386 has a much lower apparent H-alpha
luminosity than this component. The nucleus is probably highly absorbed.
Although the majority of the Narrow-Line Region components follows a regular
velocity field, we find evidence for a separate kinematic component. The
Narrow-Line Region is aligned anti-parallel to the radio-jet which propagates
from the center of NGC1386 to the south.
(258kb)

astro-ph/0008270 [abs, src, ps, other] :

Title: Mixing through shear instabilities
Authors:
M. Brüggen (MPA, Churchill College),
W. Hillebrandt (MPA)
Comments: 9 pages, 12 figures, accepted by MNRAS

In this paper we present the results of numerical simulations of the
Kelvin-Helmholtz instability in a stratified shear layer. This shear
instability is believed to be responsible for extra mixing in differentially
rotating stellar interiors and is the prime candidate to explain the abundance
anomalies observed in many rotating stars. All mixing prescriptions currently
in use are based on phenomenological and heuristic estimates whose validity is
often unclear. Using three-dimensional numerical simulations, we study the
mixing efficiency as a function of the Richardson number and compare our
results with some semi-analytical formalisms of mixing.
(125kb)

astro-ph/0008271 [abs, src, ps, other] :

Title: Validation of Up-the-Ramp Sampling with Cosmic Ray Rejection on IR
Detectors
Authors:
J. D. Offenberg,
D. J. Fixsen,
B. J. Rauscher,
W. J. Forrest,
R. J. Hanisch,
J. C. Mather,
M. E. McKelvey,
R. E. McMurray,
M. A. Nieto-Santisteban,
J. L. Pipher,
R. Sengupta,
H. S. Stockman
Comments: 25 pages, 12 figures. Submitted to the PASP

We examine cosmic ray rejection methodology on data collected from InSb and
Si:As detectors. The application of an Up-the-Ramp sampling technique with
on-the-fly cosmic ray identification and mitigation is the focus of this study.
This technique is valuable for space-based observatories which are exposed to
high-radiation environments. We validate the Up-the-Ramp approach on
radiation-test data sets with InSb and Si:As detectors which were generated for
SIRTF. The Up-the-Ramp sampling method studied in this paper is over 99.9%
effective at removing cosmic rays and preserves the structure and photometric
quality of the image to well within the measurement error.
(309kb)

astro-ph/0008272 [abs, src, ps, other] :

Title: Blue horizontal branch stars in metal-rich globular clusters. II. 47 Tuc
and NGC 362
Authors:
S. Moehler,
W.B. Landsman,
B. Dorman
Comments: 8 pages, 3 figures, uses aa.cls (included), A&A in press

Atmospheric parameters (effective temperature, surface gravity) and radial
velocities are derived for 12 candidate blue horizontal branch (HB) stars in
the globular clusters 47 Tuc and NGC 362, which so far have been known to
contain primarily red HB stars. The spectroscopic targets were selected from
the catalog of hot stars detected in these clusters at 1600 A using the
Ultraviolet Imaging Telescope (UIT). Spectroscopic analyses of these stars
reveal, however, that one of the four HB candidate targets in 47 Tuc, and five
out of the eight targets in NGC 362 are probably background stars belonging to
the Small Magellanic Cloud. With the exception of the photometric binary
MJ38529 in 47 Tuc, the parameters of those stars that are probable members of
47 Tuc and NGC 362 agree well with canonical HB evolution. The three hot stars
in 47 Tuc all have 10,000 K < Teff < 15,000 K and include one photometric
binary, which suggests that they might have a different physical origin than
the dominant red HB population. The somewhat cooler blue HB stars in NGC 362
show more continuity with the dominant red HB population and might simply arise
from red giants with unusually high mass loss.
(91kb)

astro-ph/0008273 [abs, src, ps, other] :

Title: The Broad-Line and Narrow-Line Regions of the LINER NGC 4579
Authors:
A.J. Barth,
L.C. Ho,
A.V. Filippenko,
H.-W. Rix,
W.L.W. Sargent
Comments: 8 pages, includes 3 figures. To appear in The Astrophysical Journal

We report the discovery of an extremely broad H-alpha emission line in the
LINER nucleus of NGC 4579. From ground-based observations, the galaxy was
previously known to contain a Type 1 nucleus with a broad H-alpha line of FWHM
= 2300 km/s and FWZI ~ 5000 km/s. New spectra obtained with the Hubble Space
Telescope and a 0.2 arcsec-wide slit reveal an H-alpha component with FWZI ~
18,000 km/s. The line is not obviously double-peaked, but it does possess
shoulders on the red and blue sides which resemble the H-alpha profiles of
double-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggests
that the very broad H-alpha profile in NGC 4579 may represent emission from an
accretion disk. Three such objects have been found recently in two HST programs
which have targeted a total of 30 galaxies, demonstrating that double-peaked or
extremely broad-line emission in LINERs must be much more common than would be
inferred from ground-based surveys. The ratio of the narrow [S II] 6716, 6731
lines shows a pronounced gradient indicating a steep rise in density toward the
nucleus. The direct detection of a density gradient within the inner arcsecond
of the narrow-line region confirms expectations from previous observations of
linewidth-critical density correlations in several LINERs.
(80kb)

astro-ph/0008274 [abs, src, ps, other] :

Title: ASCA Observations of GX 354-0 and KS 1731-260
Authors:
T. Narita (1),
J.E. Grindlay (1),
D. Barret (2), ((1) CfA, (2) CESR)
Comments: Accepted for publication in the Astrophysical Journal

We report on ASCA observations of the low mass X-ray binaries GX 354-0 and KS
1731-260. The spectrum of GX 354-0 is best described as a power-law or a
Comptonized spectrum with tau ~ 5 and kT ~ 8 keV and a residual at ~6.5 keV.
The residual may be a disk reflection or a Compton broadened Gaussian line from
the hot inner ADAF-like coronal region. The absorption column density to the
source is 2.9e22 cm^-2. No soft thermal component was detected. The spectrum
from KS 1731-260 is softer and it is best fit with a two component model with a
column density of 1.1e22 cm^-2. The likely interpretation is emission from a
Comptonizing cloud with an optical depth tau>12 and either a neutron star or a
disk blackbody emission. We discuss the likely location of the Comptonizing
cloud for both sources within the context of several proposed emission models.
(192kb)

astro-ph/0008275 [abs, src, ps, other] :

Title: Development of Gold Contacted Flip-chip Detectors with IMARAD CZT
Authors:
T. Narita,
P.F. Bloser,
J.E. Grindlay,
J.A. Jenkins (CfA)
Comments: To appear in Proc. SPIE 4141, “Hard X-ray, Gamma-Ray, and Neutron
Detector Physics II”

We present initial results from our evaluation of a gold-contacted pixellated
detector using cadmium zinc telluride substrate produced by IMARAD Imaging
Systems. The Horizontal Bridgman (HB) grown crystals from IMARAD have been
shown to produce high resolution photopeaks, but they are also seen to have
large leakage current. Our previous tests with IMARAD CZT showed that the use
of indium anodes and gold cathode improved the resistivity compared to the
standard indium-contacted detectors. We seek to test whether simple evaporated
gold contacts alone could also reduce the leakage current and thus improve the
spectral resolution, especially in the 10-100 keV energy range. We have
fabricated several metal-semiconductor-metal (MSM) detectors with a 4×4 array
of pixels on 10×10 mm substrates. Measurements of the detectors’ leakage
current, spectral response, and temperature sensitivity are presented and
compared to IMARAD’s ohmic contact detector and gold contact MSM detectors made
of High Pressure Bridgman (HPB) material. Finally, we show preliminary results
from a tiled flip-chip pixellated detector made using the IMARAD detectors.
(560kb)

astro-ph/0008276 [abs, src, ps, other] :

Title: Star Formation History in the Nicmos Northern Hubble Deep Field
Authors:
Rodger I. Thompson,
Ray J. Weymann,
Lisa J. Storrie-Lombardi
Comments: Accepted for publication in the Astrophysical Journal

This paper presents the star formation history in the NICMOS Northern Deep
HDF. It uses the techniques of photometric redshifts and extinctions to correct
for extinction of the ultra-violet flux. It presents a new method for
correcting for surface brightness diming. It also predicts the 850 micron
fluxes of the objects for comparison with SCUBA measurements
(210kb)

astro-ph/0008277 [abs, src, ps, other] :

Title: A New Angle on Gravitational Clustering
Authors:
Roman Scoccimarro
Comments: 12 pages, 4 figures. To appear in the proceedings of the 15th Florida
Workshop in Nonlinear Astronomy and Physics, “The Onset of Nonlinearity”

We describe a new approach to gravitational instability in large-scale
structure, where the equations of motion are written and solved as in field
theory in terms of Feynman diagrams. The basic objects of interest are the
propagator (which propagates solutions forward in time), the vertex (which
describes non-linear interactions between waves) and a source with prescribed
statistics which describes the effect of initial conditions. We show that loop
corrections renormalize these quantities, and discuss applications of this
formalism to a better understanding of gravitational instability and to
improving non-linear perturbation theory in the transition to the non-linear
regime. We also consider the role of vorticity creation due to shell-crossing
and show using N-body simulations that at small (virialized) scales the
velocity field reaches equipartition, i.e. the vorticity power spectrum is
about twice the divergence power spectrum.
(25kb)

astro-ph/0008278 [abs, src, ps, other] :

Title: Protoplanetary disks around Herbig Ae/Be stars: Indications from ISO
spectroscopy
Authors:
M.E. van den Ancker (CfA)
Comments: 3 pages, 1 figure, to appear in “Planetary Systems in the Universe:
Observation, Formation and Evolution”, eds. A. Penny, P. Artymowicz, A.-M.
Lagrange and S Russell, ASP Conf. Series, in press

An analysis of solid-state features in infrared spectra of 46 Herbig Ae/Be
stars is presented. The presence of solid-state emission bands is compared to
other indicators of circumstellar material, such as Halpha emission, optical
variability and sub-mm continuum fluxes. The correlation between these
different indicators is weak, if present at all, in our sample. However, a
strong dependence on spectral type of the central star seems to be present:
stars with spectral type earlier than B9 show either amorphous silicate in
absorption or infrared spectra dominated by PAH emission, whereas more than 70%
of the stars of later spectral type show silicate emission. We conclude that
the infrared spectrum of Herbig Be stars is in general dominated by emission
from the circumstellar envelope, whereas the lower-mass Herbig Ae stars show a
spectrum that is dominated by a disk that is passively heated by the central
star.
(14kb)

astro-ph/0008279 [abs, src, ps, other] :

Title: HEXTE Detections of Hard X-Ray Tails in Sco X-1
Authors:
F. D’Amico (1 and 2),
W. A. Heindl (1),
R. E. Rothschild (1),
D. E. Gruber (1) ((1) UCSD, La Jolla, USA, (2) INPE, S. J. dos Campos, Brazil)
Comments: 15 pages, 1 .ps figure; uses aastex; submitted to ApJ Letters

We report the detection of a non-thermal hard X-ray component from Sco X-1
based upon the analysis of 20-220 keV spectra obtained with the HEXTE
experiment onboard the RXTE satellite. We find that the addition of a power-law
component to a thermal bremsstrahlung model is required to achieve a good fit
in 5 of 16 observations analyzed. Using PCA data we were able to track the
movement of the source along the Z diagram, and we found that the presence of
the hard X-ray tail is not confined to a specific Z position. However, we do
observe an indication that the power law index hardens with increasing mass
accretion rate, as indicated from the position on the Z diagram. We find that
the derived non-thermal luminosities are about 10% of that derived for the
brightest of the atoll sources. These observations provide firm evidence for
non-thermal X-ray activity in a Z source.
(14kb)

astro-ph/0008280 [abs, src, ps, other] :

Title: Infrared L Band Observations of the Trapezium Cluster: A Census of
Circumstellar Disks and Candidate Protostars
Authors:
Charles J. Lada,
August A. Muench,
Karl E. Haisch Jr.,
Elizabeth A. Lada,
Joao F. Alves,
Eric V. Tollestrup,
S. P. Willner
Comments: 33 pages plus 3 separate color figures. For higher resolution color
figures and a single file containing the entire paper, figures and tables see
this http URL Used
AASTEX macros v 5.0. Paper will appear in December AJ

We report the results of a sensitive near-infrared JHKL imaging survey of the
Trapezium cluster in Orion. We use the JHKL colors to obtain a census of
infrared excess stars in the cluster. Of (391) stars brighter than 12th
magnitude in the K and L bands, 80 +/- 7% are found to exhibit detectable
infrared excess on the J-H, K-L color-color diagram. Examination of a subsample
of 285 of these stars with published spectral types yields a slightly higher
infrared excess fraction of 85%. We find that 97% of the optical proplyds in
the cluster exhibit excess in the JHKL color-color diagram indicating that the
most likely origin of the observed infrared excesses is from circumstellar
disks. We interpret these results to indicate that the fraction of stars in the
cluster with circumstellar disks is between 80-85%. Moreover, we find that the
probability of finding an infrared excess/protoplanetary disk around a star is
independent of stellar mass over essentially the entire range of the stellar
mass function down to the hydrogen burning limit. We identify 78 stars in our
sample characterized by K-L colors suggestive of deeply embedded protostellar
objects. If even a modest fraction fraction (i.e., ~ 50%) of these objects are
protostars, then star formation could be continuing in the molecular ridge at a
rate comparable to that which produced the foreground Trapezium cluster.
(297kb)

astro-ph/0008281 [abs, src, ps, other] :

Title: Cosmological-Model-Parameter Determination from Satellite-Acquired Type
Ia and IIP Supernova Data
Authors:
Silviu Podariu,
Peter Nugent,
Bharat Ratra
Comments: 16 pages, 6 figures

We examine the constraints that satellite-acquired Type Ia and IIP supernova
apparent magnitude versus redshift data will place on cosmological model
parameters in models with and without a constant or time-variable cosmological
constant $Lambda$. High-quality data which could be acquired in the near
future will result in tight constraints on these parameters. For example, if
all other parameters of a spatially-flat model with a constant $Lambda$ are
known, the supernova data should constrain the non-relativistic matter density
parameter $Omega_0$ to better than 1% (2%, 0.5%) at 1$sigma$ with neutral
(worst case, best case) assumptions about data quality.
(90kb)

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Cross-listings

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cond-mat/0008190 [abs, src, ps, other] :

Title: Schulman Replies
Authors:
L. S. Schulman
Subj-class: Statistical Mechanics
Journal-ref: Phys. Rev. Lett. 85, 897 (2000)

This is a reply to a comment of Casati, Chirikov and Zhirov (PRL 85, 896
(2000)) on PRL 83, 5419 (1999).

The suitability of the particlar two-time boundary value problem used in the
earlier PRL is argued.
(3kb)

hep-ph/0006088 [abs, src, ps, other] :

Title: Random values of the cosmological constant
Authors:
John F. Donoghue
Comments: 17 pages, Comments (and references) added on quantum fluctuations and
eternal inflation, and the discussion of Hubble damping has been modified
significantly

One way that an anthropic selection mechanism may be manifest in a physical
theory involves multiple domains in the universe with different values of the
physical parameters. If this mechanism is to be relevant for understanding the
small observed value of the cosmological constant, it may involve a mechanism
by which some contributions to the cosmological constant can be fixed at a
continuous range of values in the different domains. I study the properties of
four possible mechanisms, including the possibility of the Hubble damping of a
scalar field with an extremely flat potential. Another interesting possibility
involves fixed random values of non-dynamical form fields, and a cosmological
mechanism is suggested. This case raises the possibility of anthropic selection
of other parameters in addition. Further requirements needed for a consistent
cosmology are discussed.
(18kb)

hep-ph/0008145 [abs, src, ps, other] :

Title: Latest cosmological constraints on the densities of hot and cold dark
matter
Authors:
Max Tegmark,
Matias Zaldarriaga,
Andrew J. S. Hamilton
Comments: 9 pages, 6 figs. Power spectrum movies at
this http URL or from max@physics.upenn.edu.
To appear in “Sources and Detection of Dark Matter/Energy in the Universe”,
ed. D. B. Cline (Springer, Berlin, 2000)

As experimentalists step up their pursuit of cold dark matter particles and
neutrino masses, cosmological constraints are tightening. We compute the joint
constraints on 11 cosmological parameters from cosmic microwave background and
large scale structure data, and find that at 95% confidence, the total
(cold+hot) dark matter density is h^2 Omega_dark = 0.20 +.12 -.10 with at most
38% of it being hot (due to neutrinos). A few assumptions, including negligible
neutrinos, tighten this measurement to h^2 Omega_dark = 0.13 +0.04 -0.02, i.e,
2.4e-27 kg/m^3 give or take 20%.
(387kb)

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Replacements

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astro-ph/9910273 [abs, src, ps, other] :

Title: Pulse Width Evolution in GRBs: Evidence for Internal Shocks
Authors:
E. Ramirez-Ruiz (IoA Cambridge),
E. E. Fenimore (Los Alamos)
Comments: 20 pages, 7 embedded figures, with final revisions
Journal-ref: ApJ, 539, 712,2000
Note: replaced with revised version Thu, 17 Aug 2000 15:56:24 GMT (49kb)

gr-qc/9912028 [abs, src, ps, other] :

Title: The field equation from Newton’s law of motion and absence of magnetic
monopole
Authors:
Parampreet Singh,
Naresh Dadhich
Comments: 14 pages, revised version. To appear in Int. J. Mod. Phys. A
Subj-class: General Relativity and Quantum Cosmology; Classical Physics
Note: replaced with revised version Thu, 17 Aug 2000 05:15:32 GMT (11kb)

hep-th/9903236 [abs, src, ps, other] :

Title: The Statistical Mechanics of the Self-Gravitaing Gas: Equation of State
and Fractal Dimension
Authors:
H. J. de Vega,
N. S’anchez
Comments: LaTex, 7 pages, 2 .ps figures, minor improvements, to appear in
Physics Letters B
Note: replaced with revised version Thu, 17 Aug 2000 13:59:47 GMT (17kb)

astro-ph/0006107 [abs, src, ps, other] :

Title: R-modes of neutron stars with a solid crust
Authors:
Shijun Yoshida,
Umin Lee
Comments: 11 pages, 3 figures, submitted to ApJ
Note: replaced with revised version Thu, 17 Aug 2000 05:20:26 GMT (37kb)

astro-ph/0006376 [abs, src, ps, other] :

Title: Quasar Str”omgren Spheres Before Cosmological Reionization
Author:
Renyue Cen,
Zoltan Haiman (Princeton University Observatory)
Comments: revised, accepted to ApJ Letters
Note: replaced with revised version Thu, 17 Aug 2000 06:04:53 GMT (30kb)

astro-ph/0008184 [abs, src, ps, other] :

Title: The Edinburgh/Durham Southern Galaxy Catalogue – IX. The Galaxy
Catalogue
Authors:
R. C. Nichol (Carnegie Mellon Univ.),
C. A. Collins, (ARI, Liverpool John Moores Univ.),
S. L. Lumsden (Univ. of Leeds)
Comments: Submitted to ApJS. The catalogue can be obtained from
this http URL
Note: replaced with revised version Thu, 17 Aug 2000 11:49:06 GMT (53kb)

hep-ph/0005216 [abs, src, ps, other] :

Title: Self-organized criticality in atmospheric cascades
Authors:
M.Rybczynski,
Z.Wlodarczyk,
G.Wilk
Comments: gz-compressed .tar file containing LaTeX file and 5 PS files with
figures, 4 pages altogether (Nucl. Phys. B style, espcrc2.sty file attached)
Presented at XI International Symposium On Very High Energy Cosmic Ray
Interaction, Campinas, Brazil, July 17-21, 2000. To be published in Nucl.
Phys. B (Proc. Suppl.). Some typos corrected
Note: replaced with revised version Thu, 17 Aug 2000 14:35:05 GMT (33kb)

hep-ph/0005217 [abs, src, ps, other] :

Title: Muons from strangelets
Authors:
M.Rybczynski,
Z.Wlodarczyk,
G.Wilk
Comments: gz-compressed .tar file containing LaTeX file and 3 PS files with
figures, 4 pages altogether (Nucl. Phys. B style, espcrc2.sty file attached)
Presented at XI International Symposium On Very High Energy Cosmic Ray
Interaction, Campinas, Brazil, July 17-21, 2000. To be published in Nucl.
Phys. B (Proc. Suppl.). Some typos corrected
Note: replaced with revised version Thu, 17 Aug 2000 14:37:02 GMT (54kb)

hep-ph/0008138 [abs, src, ps, other] :

Title: Heavy sterile neutrinos: Bounds from big-bang nucleosynthesis and SN
1987A
Authors:
A.D. Dolgov,
S.H. Hansen,
G. Raffelt,
D.V. Semikoz
Comments: 19 pages, 5 figures, 1 table. Some references added
Note: replaced with revised version Thu, 17 Aug 2000 10:04:48 GMT (31kb)

hep-th/0005239 [abs, src, ps, other] :

Title: Evolution of Cosmological Perturbations in the Brane World
Authors:
Kazuya Koyama,
Jiro Soda
Comments: 25 pages, 4 figures, typos corrected, version to appear in Physical
Review D
Note: replaced with revised version Thu, 17 Aug 2000 02:07:31 GMT (26kb)

nucl-th/0003008 [abs, src, ps, other] :

Title: Kaon Condensation in Proto-Neutron Star Matter
Authors:
J.A. Pons,
S. Reddy,
Related