548 research outputs found
Silicon abundance from RESIK solar flare observations
The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and
active region X-ray spectra in four channels covering the wavelength range 3.8
-- 6.1 \AA in its operational period between 2001 and 2003. Several highly
ionized silicon lines were observed within the range of the long-wavelength
channel (5.00 -- 6.05 \AA). The fluxes of the \sixiv Ly- line (5.217
\AA) and the \sixiii line (5.688 \AA) during 21 flares with
optimized pulse-height analyzer settings on RESIK have been analyzed to obtain
the silicon abundance relative to hydrogen in flare plasmas. As in previous
work, the emitting plasma for each spectrum is assumed to be characterized by a
single temperature and emission measure given by the ratio of emission in the
two channels of GOES. The silicon abundance is determined to be (\sixiv) and (\sixiii) on a logarithmic scale with
H = 12. These values, which vary by only very small amounts from flare to flare
and times within flares, are and times the
photospheric abundance, and are about a factor of three higher than RESIK
measurements during a period of very low activity. There is a suggestion that
the Si/S abundance ratio increases from active regions to flares.Comment: To be published, Solar Physic
Sphinx measurements of the 2009 solar minimum x-ray emission
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured
soft X-ray emission in the 1-15 keV energy range during the deep solar minimum
of 2009 with a sensitivity much greater than GOES. Several intervals are
identified when the X-ray flux was exceptionally low, and the flux and solar
X-ray luminosity are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3
and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general coronal
structures rather than confined features like bright points. For one of 27
intervals of exceptionally low activity identified in the SphinX data, the
Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT
(0.1-2.4 keV) was less than most nearby K and M dwarfs.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
Si XII X-Ray Satellite Lines in Solar Flare Spectra
The temperature dependence of the Si XII n = 3 and 4 dielectronic satellite line features at 5.82 and 5.56 A, respectively, near the Si XIII 1s2-1s3p and 1s2-1s4p lines (5.681 and 5.405 A), is calculated using atomic data presented here. The resulting theoretical spectra are compared with solar flare spectra observed by the RESIK spectrometer on the CORONAS-F spacecraft. The satellites, like the more familiar n = 2 satellites near the Si XIII 1s2-1s2p lines, are formed mostly by dielectronic recombination, but unlike the n = 2 satellites, are unblended. The implications for similar satellite lines in flare Fe spectra are discussed
New challenges for the pressure evolution of the glass temperature
The ways of portrayal of the pressure evolution of the glass temperature (Tg)
beyond the dominated Simon-Glatzel-like pattern are discussed. This includes
the possible common description of Tg(P) dependences in systems described by
dtg/dP>0 and dTg/dP<0. The latter is associated with the maximum of Tg(P) curve
hidden in the negative pressures domain. The issue of volume and density
changes along the vitrification curve is also noted. Finally, the universal
pattern of vitrification associated with the crossover from the low density
(isotropic stretching) to the high density (isotropic compression) systems is
proposed. Hypothetically, it may obey any glass former, from molecular liquids
to colloids
A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer
The {\em Bent Crystal Spectrometer}\/ (BCS) on the NASA {\em Solar Maximum
Mission}\/ spacecraft observed the X-ray spectra of numerous solar flares
during the periods 1980 February to November and 1984~--~1989. The instrument,
the first of its kind to use curved crystal technology, observed the resonance
lines of He-like Ca (\caxix) and Fe (\fexxv) and neighboring satellite lines,
allowing the study of the rapid evolution of flare plasma temperature,
turbulence, mass motions etc. To date there has not been a solar X-ray
spectrometer with comparable spectral and time resolution, while subsequent
solar cycles have delivered far fewer and less intense flares. The BCS data
archive thus offers an unparalleled resource for flare studies. A recent
re-assessment of the BCS calibration and its operations is extended here by
using data during a spacecraft scan in the course of a flare on 1980 November~6
that highlights small deformations in the crystal curvature of the important
channel~1 (viewing lines of \caxix\ and satellites). The results explain
long-standing anomalies in spectral line ratios which have been widely
discussed in the past. We also provide an in-flight estimation of the BCS
collimator field of view which improves the absolute intensity calibration of
the BCS. The BCS channel~1 background is shown to be entirely due to solar
continuum radiation, confirming earlier analyses implying a time-variable flare
abundance of Ca. We suggest that BCS high-resolution \caxix\ and \fexxv\ line
spectra be used as templates for the analysis of X-ray spectra of non-solar
sources.Comment: To be published, Astrophysical Journa
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