925 research outputs found
GALEX Observations of CS and OH Emission in Comet 9P/Tempel 1 During Deep Impact
GALEX observations of comet 9P/Tempel 1 using the near ultraviolet (NUV)
objective grism were made before, during and after the Deep Impact event that
occurred on 2005 July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was
maneuvered into the path of the comet. The NUV channel provides usable spectral
information in a bandpass covering 2000 - 3400 A with a point source spectral
resolving power of approximately 100. The primary spectral features in this
range include solar continuum scattered from cometary dust and emissions from
OH and CS molecular bands centered near 3085 and 2575 A, respectively. In
particular, we report the only cometary CS emission detected during this event.
The observations allow the evolution of these spectral features to be tracked
over the period of the encounter. In general, the NUV emissions observed from
Tempel 1 are much fainter than those that have been observed by GALEX from
other comets. However, it is possible to derive production rates for the parent
molecules of the species detected by GALEX in Tempel 1 and to determine the
number of these molecules liberated by the impact. The derived quiescent
production rates are Q(H2O) = 6.4e27 molecules/s and Q(CS2) = 6.7e24
molecules/s, while the impact produced an additional 1.6e32 H2O molecules and
1.3e29 CS2 molecules, a similar ratio as in quiescent outgassing.Comment: 15 pages, 4 figures, accepted for publication in the Astrophysical
Journa
A polarity reversal in the large-scale magnetic field of the rapidly rotating Sun HD 190771
Aims. We investigate the long-term evolution of the large-scale photospheric
magnetic field geometry of the solar-type star HD 190771. With fundamental
parameters very close to those of the Sun except for a shorter rotation period
of 8.8 d, HD 190771 provides us with a first insight into the specific impact
of the rotation rate in the dynamo generation of magnetic fields in 1
stars.
Methods. We use circularly polarized, high-resolution spectra obtained with
the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France) and compute
cross-correlation line profiles with high signal-to-noise ratio to detect
polarized Zeeman signatures. From three phase-resolved data sets collected
during the summers of 2007, 2008, and 2009, we model the large-scale
photospheric magnetic field of the star by means of Zeeman-Doppler imaging and
follow its temporal evolution.
Results. The comparison of the magnetic maps shows that a polarity reversal
of the axisymmetric component of the large-scale magnetic field occurred
between 2007 and 2008, this evolution being observed in both the poloidal and
toroidal magnetic components. Between 2008 and 2009, another type of global
evolution occured, characterized by a sharp decrease of the fraction of
magnetic energy stored in the toroidal component. These changes were not
accompanied by significant evolution in the total photospheric magnetic energy.
Using our spectra to perform radial velocity measurements, we also detect a
very low-mass stellar companion to HD 190771.Comment: Accepted by Astronomy and Astrophysics (Letter to the Editor
Dynamics of light propagation in spatiotemporal dielectric structures
Propagation, transmission and reflection properties of linearly polarized
plane waves and arbitrarily short electromagnetic pulses in one-dimensional
dispersionless dielectric media possessing an arbitrary space-time dependence
of the refractive index are studied by using a two-component, highly symmetric
version of Maxwell's equations. The use of any slow varying amplitude
approximation is avoided. Transfer matrices of sharp nonstationary interfaces
are calculated explicitly, together with the amplitudes of all secondary waves
produced in the scattering. Time-varying multilayer structures and
spatiotemporal lenses in various configurations are investigated analytically
and numerically in a unified approach. Several new effects are reported, such
as pulse compression, broadening and spectral manipulation of pulses by a
spatiotemporal lens, and the closure of the forbidden frequency gaps with the
subsequent opening of wavenumber bandgaps in a generalized Bragg reflector
Electronic and Optical Materials and Applications
Contains research objectives and reports on five research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)United States Air Force (Contract F19628-79-C-0047
Copeptin is associated with mortality and outcome in patients with acute intracerebral hemorrhage
Spontaneous intracerebral hemorrhage (ICH) accounts for a high mortality and morbidity. Early prediction of outcome is crucial for optimized care and treatment decision. Copeptin, the C-terminal part of provasopressin, has emerged as a new prognostic marker in a variety of diseases, but its prognostic value in ICH is unknown
Microwave and Quantum Magnetics
Contains research objectives and reports on five research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003)National Institutes of Health (Grant 1 P01 CA3 1303-01
GALEX FUV Observations of Comet C/2004 Q2 (Machholz): The Ionization Lifetime of Carbon
We present a measurement of the lifetime of ground state atomic carbon,
C(^3P), against ionization processes in interplanetary space and compare it to
the lifetime expected from the dominant physical processes likely to occur in
this medium. Our measurement is based on analysis of a far ultraviolet (FUV)
image of comet C/2004 Q2 (Machholz) recorded by the Galaxy Evolution Explorer
(GALEX) on 2005 March 1. The bright CI 1561 A and 1657 A multiplets dominate
the GALEX FUV band. We used the image to create high S/N radial profiles that
extended beyond one million km from the comet nucleus. Our measurements yielded
a total carbon lifetime of 7.1 -- 9.6 x 10^5 s (scaled to 1 AU). Which compares
favorably to calculations assuming solar photoionization, solar wind proton
change exchange and solar wind electron impact ionization are the dominant
processes occurring in this medium and that comet Machholz was embedded in the
slow solar wind. The shape of the CI profiles inside 3x10^5 km suggests that
either the CO lifetime is shorter than previously thought and/or a
shorter-lived carbon-bearing parent molecule, such as CH_4 is providing the
majority of the carbon in this region of the coma of comet Machholz.Comment: 26 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Microwave and Quantum Magnetics
Contains research objectives and reports on five research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003)National Institutes of Health (Grant 1 P01 CA3 1303-01
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