649 research outputs found
RESIK observations of He-like Ar X-ray line emission in solar flares
The Ar XVII X-ray line group principally due to transitions 1s2 - 1s2l (l=s,
p) near 4 Anstroms was observed in numerous flares by the RESIK bent crystal
spectrometer aboard CORONAS-F between 2001 and 2003. The three line features
include the Ar XVII w (resonance line), a blend of x and y (intercombination
lines), and z (forbidden line), all of which are blended with Ar XVI
dielectronic satellites. The ratio G, equal to [I(x+y) + I(z)]/I(w), varies
with electron temperature Te mostly because of unresolved dielectronic
satellites. With temperatures estimated from GOES X-ray emission, the observed
G ratios agree fairly well with those calculated from CHIANTI and other data.
With a two-component emission measure, better agreement is achieved. Some S XV
and S XVI lines blend with the Ar lines, the effect of which occurs at
temperatures greater than 8MK, allowing the S/Ar abundance ratio to be
determined. This is found to agree with coronal values. A nonthermal
contribution is indicated for some spectra in the repeating-pulse flare of 2003
February 6.Comment: Latex file and 3 ps files. Astrophysical Journal Letters (accepted,
June 2008
Soft X-ray coronal spectra at low activity levels observed by RESIK
The quiet-Sun X-ray emission is important for deducing coronal heating
mechanisms, but it has not been studied in detail since the Orbiting Solar
Observatory (OSO) spacecraft era. Bragg crystal spectrometer X-ray observations
have generally concentrated on flares and active regions. The high sensitivity
of the RESIK (REntgenovsky Spectrometer s Izognutymi Kristalami) instrument on
the CORONAS-F solar mission has enabled the X-ray emission from the quiet
corona to be studied in a systematic way for the first time. Our aim is to
deduce the physical conditions of the non-flaring corona from RESIK line
intensities in several spectral ranges using both isothermal and multithermal
assumptions. We selected and analyzed spectra in 312 quiet-Sun intervals in
January and February 2003, sorting them into 5 groups according to activity
level. For each group, the fluxes in selected spectral bands have been used to
calculate values parameters for the best-fit that lead to a intensities
characteristic of each group. We used both isothermal and multitemperature
assumptions, the latter described by differential emission measure (DEM)
distributions. RESIK spectra cover the wavelength range (3.3-6.1 A). This
includes emission lines of highly ionized Si, S, Cl, Ar, and K, which are
suitable for evaluating temperature and emission measure, were used. The RESIK
spectra during these intervals of very low solar activity for the first time
provide information on the temperature structure of the quiet corona. Although
most of the emission seems to arise from plasma with a temperature between 2MK
and 3MK, there is also evidence of a hotter plasma (T approx. 10MK) with an
emission measure 3 orders smaller than the cooler component. Neither coronal
nor photospheric element abundances appear to describe the observed spectra
satisfactorily.Comment: Submitting 1 Latex and 7 figure file
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
A solar spectroscopic absolute abundance of argon from RESIK
Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949
Angstroms and 3.733 Angstroms respectively with the RESIK X-ray spectrometer on
the CORONAS-F spacecraft, together with temperatures and emission measures from
the two channels of GOES, have been analyzed to obtain the abundance of Ar in
flare plasmas in the solar corona. The line fluxes per unit emission measure
show a temperature dependence like that predicted from theory, and lead to
spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44
pm 0.07 (Ar XVII) and 6.49 pm 0.16 (Ar XVIII) which are in agreement to within
uncertainties. The weighted mean is 6.45 pm 0.06, which is between two recent
compilations of the solar Ar abundance and suggest that the photospheric and
coronal abundances of Ar are very similar.Comment: 4 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
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