705 research outputs found
Radial distribution of Fe XIV emission in the Cygnus Loop
The one dimensional distribution of Fe 14 emission has been determined along a radius of the Cygnus Loop through the use of a tilting filter photometer. The observed emission extends at least 5 arc minutes outside the optical filaments. A simple Sedov solution model of the temperature and density distribution behind the shock agrees with the observations if the shock front is near the extent of the Fe 14 emission, the shock velocity is from 300 to 250/kms and the density external to the remnant is about 0.7-1.4 cm to three minus 3 power. These parameters are in reasonable agreement with X-ray maps and optical radial velocities
Quantum dynamics of the avian compass
The ability of migratory birds to orient relative to the Earth's magnetic
field is believed to involve a coherent superposition of two spin states of a
radical electron pair. However, the mechanism by which this coherence can be
maintained in the face of strong interactions with the cellular environment has
remained unclear. This Letter addresses the problem of decoherence between two
electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei.
Dynamics of the radical pair density matrix are derived and shown to yield a
simple mechanism for sensing magnetic field orientation. Rates of dephasing and
decoherence are calculated ab initio and found to yield millisecond coherence
times, consistent with behavioral experiments
Carbonylchlorido(1-methylsulfanylpenta-1,3-dien-1-yl-5-ylidene)bis(triphenylphosphane)osmium(II)
The crystal structure of the title compound, [Os(C6H7S)Cl(C18H15P)2(CO)], confirms the formulation as an osmabenzene. There is a slightly distorted octahedral coordination environment at the OsII ion, with the triphenylphosphane ligands mutually trans and the chloride cis to the carbon bearing the –SMe substituent. Within the metallacyclic ring, the C—C distances are appropriate for aromatic bonds and the two Os—C distances are shorter than typical Os—C single bonds. The maximum deviation from the least-squares plane through the osmabenzene ring occurs for the carbon bearing the SMe substituent [0.1037 (18) Å]
Coronal loop hydrodynamics. The solar flare observedon November 12 1980 revisited: the UV line emission
We revisit a well-studied solar flare whose X-ray emission originating from a
simple loop structure was observed by most of the instruments on board SMM on
November 12 1980. The X-ray emission of this flare, as observed with the XRP,
was successfully modeled previously. Here we include a detailed modeling of the
transition region and we compare the hydrodynamic results with the UVSP
observations in two EUV lines, measured in areas smaller than the XRP rasters,
covering only some portions of the flaring loop (the top and the foot-points).
The single loop hydrodynamic model, which fits well the evolution of coronal
lines (those observed with the XRP and the \FeXXI 1354.1 \AA line observed with
the UVSP) fails to model the flux level and evolution of the \OV 1371.3 \AA
line.Comment: A&A, in press, 6 pages, 5 figure
Emission Line Galaxies in the STIS Parallel Survey I: Observations and Data Analysis
In the first three years of operation STIS obtained slitless spectra of
approximately 2500 fields in parallel to prime HST observations as part of the
STIS Parallel Survey (SPS). The archive contains almost 300 fields at high
galactic latitude (|b|>30) with spectroscopic exposure times greater than 3000
seconds. This sample contains 220 fields (excluding special regions and
requiring a consistent grating angle) observed between 6 June 1997 and 21
September 2000, with a total survey area of about 160 square arcminutes. At
this depth, the SPS detects an average of one emission line galaxy per three
fields. We present the analysis of these data, and the identification of 131
low to intermediate redshift galaxies detected by optical emission lines. The
sample contains 78 objects with emission lines that we infer to be redshifted
[OII]3727 emission at 0.43<z<1.7. The comoving number density of these objects
is comparable to that of H-alpha emitting galaxies in the NICMOS parallel
observations. One quasar and three probable Seyfert galaxies are detected. Many
of the emission-line objects show morphologies suggestive of mergers or
interactions. The reduced data are available upon request from the authors.Comment: 58 preprint pages, including 26 figures; accepted for publication in
ApJ
FUSE Observations of Intrinsic Absorption in the Seyfert 1 Galaxy Mrk 509
We present far-ultraviolet spectra of the Seyfert 1 galaxy Mrk 509 obtained
in 1999 November with the Far Ultraviolet Spectroscopic Explorer (FUSE). Our
data span the observed wavelength range 915-1185 A at a resolution of ~20 km/s.
The spectrum shows a blue continuum, broad OVI 1032,1038 emission, and a broad
CIII 977 emission line. Superposed on these emission components, we resolve
associated absorption lines of OVI 1032,1038, CIII 977, and Lyman lines through
Lzeta. Seven distinct kinematic components are present, spanning a velocity
range of -440 to +170 km/s relative to the systemic velocity. The absorption is
clustered in two groups, one centered at -370m km/s and another at the systemic
velocity. The blue-shifted cluster may be associated with the extended line
emission visible in deep images of Mrk 509 obtained by Phillips et al. Although
several components appear to be saturated, they are not black at their centers.
Partial covering or scattering permits ~7% of the broad-line or continuum flux
to be unaffected by absorption. Of the multiple components, only one has the
same ionization state and column density as highly ionized gas that produces
the OVII and OVIII ionization edges in X-ray spectra of Mrk 509.
This paper will appear in a special issue of Astrophysical Journal Letters
devoted to the first scientific results from the FUSE mission.Comment: To appear in the Astrophysical Journal (Letters). 4 pages, 3 color
PostScript figures. Figures are best viewed and printed in color. Added
acknowledgment that this is one of many papers to be published in a special
issue of ApJL devoted to the first scientific results from the FUSE missio
Limits on the Optical Brightness of the Epsilon Eridani Dust Ring
The STIS/CCD camera on the {\em Hubble Space Telescope (HST)} was used to
take deep optical images near the K2V main-sequence star Eridani in
an attempt to find an optical counterpart of the dust ring previously imaged by
sub-mm observations. Upper limits for the optical brightness of the dust ring
are determined and discussed in the context of the scattered starlight expected
from plausible dust models. We find that, even if the dust is smoothly
distributed in symmetrical rings, the optical surface brightness of the dust,
as measured with the {\em HST}/STIS CCD clear aperture at 55 AU from the star,
cannot be brighter than about 25 STMAG/". This upper limit excludes some
solid grain models for the dust ring that can fit the IR and sub-mm data.
Magnitudes and positions for 59 discrete objects between 12.5" to 58"
from Eri are reported. Most if not all of these objects are likely
to be background stars and galaxies.Comment: Revision corrects author lis
FUSE and HST STIS Observations of Hot and Cold Gas in the AB Aurigae System
We present the first observations of a Herbig Ae star with a circumstellar
disk by the Far Ultraviolet Spectroscopic Explorer (FUSE), as well as a
simultaneous observation of the star obtained with the Hubble Space Telescope
Space Telescope Imaging Spectrograph (STIS). The spectra of AB Aurigae show
emission and absorption features arising from gasses that have a wide range in
temperature, from hot OVI emission to cold molecular hydrogen and CO
absorption. Emissions from the highly ionized species OVI and CIII present in
the FUSE spectrum are redshifted, while absorption features arising from
low-ionization species like OI, NI, and SiII are blueshifted and show
characteristic stellar wind line-profiles. We find the total column density of
molecular hydrogen toward AB Aur from the FUSE apectrum, N(H_2) = (6.8 +/- 0.5)
x 10^19 cm^-2. The gas kinetic temperature of the molecular hydrogen derived
from the ratio N(J=1)/N(J=0) is 65 +/- 4 K. The column density of the CO
observed in the STIS spectrum is N(CO) = (7.1 +/- 0.5) x 10^13 cm^-2, giving a
CO/H_2 ratio of (1.04 +/- 0.11) x 10^-6. We also use the STIS spectrum to find
the column density of HI, permitting us to calculate the total column density
of hydrogen atoms, the fractional abundance of H_2, and the gas-to-dust ratio.Comment: 5 pages, including 6 figures. LaTex2e (emulateapj5.sty). Accepted for
publication in ApJ Letter
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