2,140 research outputs found
Discovery of X-rays from Mars with Chandra
On 4 July 2001, X-rays from Mars were detected for the first time. The
observation was performed with the ACIS-I detector onboard Chandra and yielded
data of high spatial and temporal resolution, together with spectral
information. Mars is clearly detected as an almost fully illuminated disk, with
an indication of limb brightening at the sunward side, accompanied by some
fading on the opposite side. The morphology and the X-ray luminosity of ~4 MW
are fully consistent with fluorescent scattering of solar X-rays in the upper
Mars atmosphere. The X-ray spectrum is dominated by a single narrow emission
line, which is most likely caused by O-K_alpha fluorescence. No evidence for
temporal variability is found. This is in agreement with the solar X-ray flux,
which was almost constant during the observation. In addition to the X-ray
fluorescence, there is evidence for an additional source of X-ray emission,
indicated by a faint X-ray halo which can be traced to about three Mars radii,
and by an additional component in the X-ray spectrum of Mars, which has a
similar spectral shape as the halo. Within the available limited statistics,
the spectrum of this component can be characterized by 0.2 keV thermal
bremsstrahlung emission. This is indicative of charge exchange interactions
between highly charged heavy ions in the solar wind and exospheric hydrogen and
oxygen around Mars. Although the observation was performed at the onset of a
global dust storm, no evidence for dust-related X-ray emission was found.Comment: 11 pages, 16 figure
The thermosphere and ionosphere of Venus
Our knowledge of the upper atmosphere and ionosphere of Venus and its interaction with the solar wind has advanced dramatically over the last decade, largely due to the data obtained during the Pioneer Venus mission and to the theoretical work that was motivated by this data. Most of this information was obtained during the period 1978 through 1981, when the periapsis of the Pioneer Venus Orbiter (PVO) was still in the measurable atmosphere. However, solar gravitational perturbations will again lower the PVO periapsis into the upper atmosphere in September 1992, prior to the destruction of the spacecraft toward the end of this year. The physics and chemistry of the thermosphere and ionosphere of Venus are reviewed
Critical Test of Simulations of Charge-Exchange-Induced X-Ray Emission in the Solar System
Experimental and theoretical state-selective X-ray spectra resulting from
single-electron capture in charge exchange (CX) collisions of Ne^10+ with He,
Ne, and Ar are presented for a collision velocity of 933 km s^-1 (4.54 keV
nucleon^-1), comparable to the highest velocity components of the fast solar
wind. The experimental spectra were obtained by detecting scattered
projectiles, target recoil ions, and X-rays in coincidence; with simultaneous
determination of the recoil ion momenta. Use and interpretation of these
spectra are free from the complications of non-coincident total X-ray
measurements that do not differentiate between the primary reaction channels.
The spectra offer the opportunity to test critically the ability of CX theories
to describe such interactions at the quantum orbital angular momentum level of
the final projectile ion. To this end, new classical trajectory Monte Carlo
calculations are compared here with the measurements. The current work
demonstrates that modeling of cometary, heliospheric, planetary, and laboratory
X-ray emission based on approximate state-selective CX models may result in
erroneous conclusions and deductions of relevant parameters.Comment: 4 figure
One-Up On L1: Can X-rays Provide Longer Advanced Warning of Solar Wind Flux Enhancements Than Upstream Monitors?
Observations of strong solar wind proton flux correlations with ROSAT X-ray
rates along with high spectral resolution Chandra observations of X-rays from
the dark Moon show that soft X-ray emission mirrors the behavior of the solar
wind. In this paper, based on an analysis of an X-ray event observed by
XMM-Newton resulting from charge exchange of high charge state solar wind ions
and contemporaneous neutral solar wind data, we argue that X-ray observations
may be able to provide reliable advance warning, perhaps by as much as half a
day, of dramatic increases in solar wind flux at Earth. Like neutral atom
imaging, this provides the capability to monitor the solar wind remotely rather
than in-situ.Comment: in press in Adv. Space Research, 7 pages, 6 eps figures, resolution
reduced for Astro-ph submission, see http://lena.gsfc.nasa.gov for full
versio
UA3/3/1 Classroom Utilization / Projection of Faculty Needs for Fall 1962
Memo from Raymond Cravens to WKU president Kelly Thompson regarding classroom utilization and projections of faculty needs for fall 1962. Includes enrollment data for 1961 and estimated increases for 1962. Enrollment is broken down by department
UA3/3/1 Class Scheduling: An Analysis of the Problem and a Possible Solution
Report by Raymond Cravens submitted to WKU president Kelly Thompson regarding scheduling of classes and the possibility of implementing a trimester system
- …