Abstract
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 Å 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 Å). The fluxes of the Si xiv Ly-β line (5.217 Å) and the Si xiii 1s 2 – 1s3p line (5.688 Å) 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 A(Si)=7.93±.21 (Si xiv) and 7.89±.13 (Si xiii) 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 2.6±1.3 and 2.4±0.7 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.
Highlights
REntgenovsky Spektrometr s Izognutymi Kristalami (RESIK: Sylwester et al, 2005) was a solar X-ray crystal spectrometer onboard the CORONAS-F spacecraft operating from the time of launch (31 July 2001) until a spacecraft failure terminated the mission in May 2003
With the latter taken to be A(Si) = 7.51 ± 0.03 (Asplund et al, 2009), we find the enhancement of the flare value over the photospheric to be 2.6 ± 1.3 (Si XIV) and 2.4 ± 0.7 (Si XIII)
Our Si abundance estimates are remarkably constant from flare to flare and over the course of the development of each flare as shown by the small scatter of points in Figures 2 and 3; Table 1 shows that for the 21 flares analyzed, the GOES peak emission had a range of a factor of > 400
Summary
REntgenovsky Spektrometr s Izognutymi Kristalami (RESIK: Sylwester et al, 2005) was a solar X-ray crystal spectrometer onboard the CORONAS-F spacecraft operating from the time of launch (31 July 2001) until a spacecraft failure terminated the mission in May 2003. In previous articles reporting the analysis of RESIK spectra (see Sylwester et al, 2012 and references cited therein), we have estimated the abundances of K, Ar, Cl, and S from emission lines of helium-like or hydrogen-like ions of these elements during flares, using a method that involves assigning a “characteristic temperature” for the emitting plasma equal to that given by the ratio of the two channels of GOES. This method is applied here for the Si XIV Ly-β and Si XIII w3 lines.
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