Soft X-ray coronal spectra at low activity levels observed by RESIK - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate

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Abstract: The quiet-Sun X-ray emission is important for deducing coronal heatingmechanisms, but it has not been studied in detail since the Orbiting SolarObservatory OSO spacecraft era. Bragg crystal spectrometer X-ray observationshave generally concentrated on flares and active regions. The high sensitivityof the RESIK REntgenovsky Spectrometer s Izognutymi Kristalami instrument onthe CORONAS-F solar mission has enabled the X-ray emission from the quietcorona to be studied in a systematic way for the first time. Our aim is todeduce the physical conditions of the non-flaring corona from RESIK lineintensities in several spectral ranges using both isothermal and multithermalassumptions. We selected and analyzed spectra in 312 quiet-Sun intervals inJanuary and February 2003, sorting them into 5 groups according to activitylevel. For each group, the fluxes in selected spectral bands have been used tocalculate values parameters for the best-fit that lead to a intensitiescharacteristic of each group. We used both isothermal and multitemperatureassumptions, the latter described by differential emission measure DEMdistributions. RESIK spectra cover the wavelength range 3.3-6.1 A. Thisincludes emission lines of highly ionized Si, S, Cl, Ar, and K, which aresuitable for evaluating temperature and emission measure, were used. The RESIKspectra during these intervals of very low solar activity for the first timeprovide information on the temperature structure of the quiet corona. Althoughmost of the emission seems to arise from plasma with a temperature between 2MKand 3MK, there is also evidence of a hotter plasma T approx. 10MK with anemission measure 3 orders smaller than the cooler component. Neither coronalnor photospheric element abundances appear to describe the observed spectrasatisfactorily.

Author: B. Sylwester, J. Sylwester, K. J. H. Phillips


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