Soft X-ray coronal spectra at low activity levels observed by RESIK
Barbara Sylwester Submitted: 2010-03-15 13:13
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.
Authors: B. Sylwester, J. Sylwester, K. J. H. Phillips
Publication Status: Accepted by Astronomy and Astrophysics
Last Modified: 2010-03-16 08:28