8,051 research outputs found
Spacelab 3 vapor crystal growth experiment
The Space Shuttle Challenger, with Spacelab 3 as its payload, was launched into orbit April 29, 1985. The mission, number 51-B, emphasized materials processing in space, although a wide variety of experiments in other disciplines were also carried onboard. One of the materials processing experiments on this flight is described, specifically the growth of single crystals of mercuric iodide by physical vapor transport
Permian Foraminifera from Tunisia
22 p., 32 pl., 3 fig.http://paleo.ku.edu/contributions.htm
Permian fusulinids from Sicily
16 p., 20 pl., 1 fig.http://paleo.ku.edu/contributions.htm
Permian fusulinids from Pacific northwest and Alaska
114 p., 49 pl., 10 fig.http://paleo.ku.edu/contributions.htm
The Chandra X-ray Spectrum of the 10.6 s Pulsar in Westerlund 1: Testing the Magnetar Hypothesis
Two sensitive Chandra X-ray observations of the heavily-reddened galactic
starburst cluster Westerlund 1 in May and June 2005 detected a previously
unknown X-ray pulsar (CXO J164710.20-455217). Its slow 10.6 s pulsations,
moderate X-ray temperature kT 0.5 keV, and apparent lack of a massive
companion tentatively suggest that it is an Anomalous X-ray Pulsar (AXP). An
isothermal blackbody model yields an acceptable spectral fit but the inferred
source radius is much less than that of a neutron star, a result that has also
been found for other AXPs. We analyze the X-ray spectra with more complex
models including a model that assumes the pulsar is a strongly magnetized
neutron star (``magnetar'') with a light element atmosphere. We conclude that
the observed X-ray emission cannot be explained as global surface emission
arising from the surface of a cooling neutron star or magnetar. The emission
likely arises in one or more localized regions (``hot spots'') covering a small
fraction of the surface. We discuss these new results in the context of both
accretion and magnetar interpretations for the X-ray emission.Comment: 14 pages, 5 figures; to appear in Ap
K-shell x-ray spectroscopy of atomic nitrogen
Absolute {\it K}-shell photoionization cross sections for atomic nitrogen
have been obtained from both experiment and state-of-the-art theoretical
techniques. Due to the difficulty of creating a target of neutral atomic
nitrogen, no high-resolution {\it K}-edge spectroscopy measurements have been
reported for this important atom. Interplay between theory and experiment
enabled identification and characterization of the strong
resonance features throughout the threshold region. An experimental value
of 409.64 0.02 eV was determined for the {\it K}-shell binding energy.Comment: 4 pages, 2 graphs, 1 tabl
Observations of the 5‐day wave in the mesosphere and lower thermosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94851/1/grl7954.pd
A Single Circumbinary Disk in the HD 98800 Quadruple System
We present sub-arcsecond thermal infrared imaging of HD 98800, a young
quadruple system composed of a pair of low-mass spectroscopic binaries
separated by 0.8'' (38 AU), each with a K-dwarf primary. Images at wavelengths
ranging from 5 to 24.5 microns show unequivocally that the optically fainter
binary, HD 98800B, is the sole source of a comparatively large infrared excess
upon which a silicate emission feature is superposed. The excess is detected
only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a
best-fit black-body temperature of 150 K, indicating that most of the dust lies
at distances greater than the orbital separation of the spectroscopic binary.
We estimate the radial extent of the dust with a disk model that approximates
radiation from the spectroscopic binary as a single source of equivalent
luminosity. Given the data, the most-likely values of disk properties in the
ranges considered are R_in = 5.0 +/- 2.5 AU, DeltaR = 13+/-8 AU, lambda_0 =
2(+4/-1.5) microns, gamma = 0+/-2.5, and sigma_total = 16+/-3 AU^2, where R_in
is the inner radius, DeltaR is the radial extent of the disk, lambda_0 is the
effective grain size, gamma is the radial power-law exponent of the optical
depth, tau, and sigma_total is the total cross-section of the grains. The range
of implied disk masses is 0.001--0.1 times that of the moon. These results show
that, for a wide range of possible disk properties, a circumbinary disk is far
more likely than a narrow ring.Comment: 11 page Latex manuscript with 3 postscript figures. Accepted for
publication in Astrophysical Journal Letters. Postscript version of complete
paper also available at
http://www.hep.upenn.edu/PORG/web/papers/koerner00a.p
XMM-Newton X-ray observations of the Wolf-Rayet binary system WR 147
We present results of an ≈20-ks X-ray observation of the Wolf-Rayet (WR) binary system WR 147 obtained with XMM-Newton. Previous studies have shown that this system consists of a nitrogen-type WN8 star plus an OB companion whose winds are interacting to produce a colliding wind shock. X-ray spectra from the pn and MOS detectors confirm the high extinction reported from infrared studies and reveal hot plasma including the first detection of the Fe Kα line complex at 6.67 keV. Spectral fits with a constant-temperature plane-parallel shock model give a shock temperature kTshock= 2.7 keV (Tshock≈ 31 MK), close to but slightly hotter than the maximum temperature predicted for a colliding wind shock. Optically thin plasma models suggest even higher temperatures, which are not yet ruled out. The X-ray spectra are harder than can be accounted for using 2D numerical colliding wind shock models based on nominal mass-loss parameters. Possible explanations include: (i) underestimates of the terminal wind speeds or wind abundances, (ii) overly simplistic colliding wind models or (iii) the presence of other X-ray emission mechanisms besides colliding wind shocks. Further improvement of the numerical models to include potentially important physics such as non-equilibrium ionization will be needed to rigorously test the colliding wind interpretatio
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