Si XII X-ray Satellite Lines in Solar Flare Spectra

Details Si XII X-ray Satellite Lines in Solar Flare Spectra Si XII X-ray Satellite Lines in Solar Flare Spectra

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp23b..08p&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SP23B-08

Other

7537 Solar And Stellar Variability

Scientific paper

We demonstrate the temperature dependence of the intensity ratio of dielectronic satellite lines due to Li-like Si (Si XII) to nearby He-like Si (Si XIII) 1s2 - 1snp(n=3, 4, 5) lines emitted in solar flare X-ray spectra. These lines, which occur in the wavelength range 5.253~Å--5.818~Å, have been observed by the RESIK bent crystal spectrometer on the Russian CORONAS-F solar mission. Line features made up of several strong satellites with transitions 1s2 n'l' - 1s n'l' nl lie near the `parent' Si XIII lines, transition 1s2 1S0 - 1snp 1P1; thus, the feature at 5.818~Å is made up of several blended Si XII satellites with `spectator' electrons n'l'=2s or 2p and nl=3p or 3d, and lies on the long-wavelength side of the Si XIII 1s2 - 1s3p line at 5.681~Å. A similar n=4 satellite feature at 5.565~Å is on the long-wavelength side of the Si XIII 1s2 - 1s4p line at 5.384~Å. The Si XII satellites are formed by dielectronic recombination and direct (inner-shell) excitation. The ratio Is/IHe (Is = Si XII satellite line flux, IHe = Si XIII line flux) depends on electron temperature approximately as Te-1. The atomic data needed to calculate Is/IHe for individual n=3 and n=4 Si XII satellite lines have been calculated and will be presented in this paper; excitation mechanisms including those by dielectronic recombination and inner-shell excitation were included using the SUPERSTRUCTURE and Distorted Wave formalisms. With these and theoretical fluxes of the Si XIII lines, synthetic spectra were calculated and compared with RESIK solar flare spectra. Values of Is/IHe measured from RESIK spectra during the decay of four long-duration solar flares, together with temperatures estimated both from the ratio of the GOES channels and from the ratio of total fluxes in two of the four RESIK channels, enable a comparison to be made with theoretical curves. The agreement with the theoretical curve based on synthetic spectra is within expected uncertainties, and the Te-1 dependence is confirmed. Satellites for other Li-like ions are expected to have a similar temperature sensitivity, in particular the Li-like Fe satellites near He-like Fe lines. Although these lines have not been seen with high-resolution spectrometers, the RHESSI mission observes the whole complex during solar flares as the so-called Fe/Ni line feature; addition of these satellites to theoretical spectra from the CHIANTI code have reduced a long-standing discrepancy with intensities observed by RHESSI. KJHP acknowledges an NRC Research Associateship, and JS and BS acknowledge support from grants (2.P03D.002.22 and PBZ-KBN-054/P03/2001) of the Polish Committee for Scientific Research. RESIK is a joint project between NRL (USA), MSSL, and RAL (UK), IZMIRAN (Russia), and SRC (Poland). The CORONAS-F mission is led by the IZMIRAN Institute.

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