High spectral resolution observations of the coronal X-ray emission from the RS CVn binary σ corona borealis

Abstract

Results of the high spectral resolution observation of the RS CVn binary σ CrB, made with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory, are reported. A spectral scan in 800 - 840 eV interval shows clear presence of X-ray emission line at 826 eV identified with ¹S₀-¹P₁ transition of Fe XVII while a prominent peak at 1007 eV in the scan band 986 - 1014 eV is attributed to a blend of lines due to highly ionized iron. Using the observed fluxes of the lines and the Raymond-Smith model, best-fit values of corona temperature and volume emission measures are derived to be (6.92 with errors +0.84 and -0.75)x10⁶K and (1.74 with errors +0.55 and -0.69)x10⁵³cm^-3 respectively. Implications of these results are briefly discussed.