2,531 research outputs found
The Biochemical, Physiological, and Metabolic Evaluation of Human Subjects in a Life Support Systems Evaluator and on a Diet of Precooked Freeze Dehydrated Foods Final Report, 12 Oct. - 24 Nov. 1964
Human water, caloric, and protein requirements in simulated life support system with dietary restrictio
Ultracompact X-ray Binaries in Globular Clusters: Variability of the Optical Counterpart of X1832-330 in NGC 6652
Evidence is emerging that the luminous X-ray sources in the cores of globular
clusters may often consist of, or perhaps even as a class be dominated by,
ultracompact (P < 1 hr) binary stars. To the two such systems already known, in
NGC 6624 and NGC 6712, we now add evidence for two more. We detect large
amplitude variability in the candidate optical counterpart for the X-ray source
in the core of NGC 6652. Although the available observations are relatively
brief, the existing Hubble Space Telescope data indicate a strong 43.6 min
periodic modulation of the visible flux of semi-amplitude 30%. Further,
although the orbital period of the source in NGC 1851 is not yet explicitly
measured, we demonstrate that previous correlations of optical luminosity with
X-ray luminosity and accretion disk size, strengthened by recent data, strongly
imply that the period of that system is also less than 1 hr. Thus currently
there is evidence that 4 of the 7 globular cluster X-ray sources with
constrained periods are ultracompact, a fraction far greater than that found in
X-ray binaries the field.Comment: 10 pages including 2 figures and 1 table. Accepted for publication in
The Astrophysical Journal Letter
The Ursinus Weekly, December 18, 1916
Schaff anniversary observed on Friday • Memorial service for late Mr. Dimon • Ursinus quintet loses to Temple • Christmas in Hawaii • College directory • A Christmas hymn: the Christ child • Resolutions • On the campushttps://digitalcommons.ursinus.edu/weekly/2575/thumbnail.jp
The UV Spectrum of the Ultra-compact X-ray Binary- 4U 1627-673
We have obtained Hubble Space Telescope/STIS low-resolution ultraviolet
spectra of the X-ray pulsar 4U 1626-67 (=KZ TrA); 4U 1626-67 is unusual even
among X-ray pulsars due to its ultra-short binary period (P=41.4 min) and
remarkably low mass-function (<1.3e-6 Msun). The far-UV spectrum was exposed
for a total of 32ks and has sufficient signal-to-noise to reveal numerous broad
emission and prominent narrower absorption lines. Most of the absorption lines
are consistent in strength with a purely interstellar origin. However, there is
evidence that both CI and CIV require additional absorbing gas local to the
system. In emission, the usual prominent lines of NV and HeII are absent,
whilst both OIV and OV are relatively strong. We further identify a rarely seen
feature at ~1660A as the OIII] multiplet. Our ultraviolet spectra therefore
provide independent support for the recent suggestion that the mass donor is
the chemically fractionated core of either a C-O-Ne or O-Ne-Mg white dwarf;
this was put forward to explain the results of Chandra high-resolution X-ray
spectroscopy. The velocity profiles of the ultraviolet lines are in all cases
broad and/or flat-topped, or perhaps even double-peaked for the highest
ionization cases of O; in either case the ultraviolet line profiles are in
broad agreement with the Doppler pairs found in the X-ray spectra. Both the
X-ray and far-UV lines are plausibly formed in (or in an corona just above) a
Keplerian accretion disc; the combination of ultraviolet and X-ray spectral
data may provide a rich data set for follow-on detailed models of the disk
dynamics and ionization structure in this highly unusual low-mass X-ray pulsar
system.Comment: 15 pages, 5 figures (color but ok in greyscale), revised version with
minor changes; accepted for publication in The Astronomical Journa
Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions
As part of our campaign to determine the nature of the various source
populations of the low-luminosity globular cluster X-ray sources, we have
obtained a Chandra X-ray Observatory ACIS-S3 image of the globular cluster NGC
6440. We detect 24 sources to a limiting luminosity of ~2 times 10^31 erg/s
(0.5-2.5keV) inside the cluster's half-mass radius, all of which lie within ~2
core radii of the cluster center. We also find excess emission in and around
the core which could be due to unresolved point sources. Based upon X-ray
luminosities and colors, we conclude that there are 4-5 likely quiescent
low-mass X-ray binaries and that most of the other sources are cataclysmic
variables. We compare these results to Chandra results from other globular
clusters and find the X-ray luminosity functions differ among the clusters.Comment: 9 pages, 4 figures, accepted by ApJ, minor changes, added table of
clusters' physical parameter
A year's work in the investigation of agricultural problems : work of the Agricultural Experiment Station during the year ending June 30, 1941
Cover title
X-ray Spectroscopy of Candidate Ultracompact X-ray Binaries
We present high-resolution spectroscopy of the neutron star/low-mass X-ray
binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of
known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four
systems in which we had previously inferred an unusual Ne/O ratio in the
absorption along the line of sight, most likely from material local to the
binaries. However, our recent Chandra X-ray Observatory LETGS spectrum of 4U
1850-087 finds a Ne/O ratio by number of 0.22+/-0.05, smaller than previously
measured and consistent with the expected interstellar value. We propose that
variations in the Ne/O ratio due to source variability, as previously observed
in these sources, can explain the difference between the low- and
high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS
observation of 4U 0513-40 also shows no unusual abundance ratios in the
absorption along the line of sight. We also present spectral results from a
third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by
an absorbed power-law + blackbody model with absorption consistent with the
expected interstellar value. Finally, we present the non-detection of a fourth
candidate ultracompact binary, 4U 1905+000, with an upper limit on the source
luminosity of < 1 x 10^{32} erg s^{-1}. Using archival data, we show that the
source has entered an extended quiescent state.Comment: 8 pages, 3 figures, accepted for publication to the Astrophysical
Journa
Casimir forces between cylinders at different temperatures
We study Casimir interactions between cylinders in thermal non-equilibrium,
where the objects as well as the environment are held at different
temperatures. We provide the general formula for the force, in a one reflection
approximation, for cylinders of arbitrary radii and optical properties. As is
the case for equilibrium, we find that the force for optically diluted
cylinders can be obtained by appropriate summation of the corresponding result
for spheres. We find that the non-equilibrium forces are generally larger than
their equilibrium counterpart at separations greater than the thermal
wavelength. They may also exhibit oscillations as function of separation,
leading to stable points of zero net force. These effects are particularly
pronounced for thin conducting cylinders (e.g. 40nm diameter nano-wires of
tungsten) due to their large emissivity.Comment: 10 pages, 5 figure
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