Capella Corona Revisited: A Combined View fromXMM‐NewtonRGS andChandraHETGS and LETGS

We present a combined analysis of the X-ray emission of the Capella coronaobtained with \textit{XMM-Newton} RGS, \textit{Chandra} HETGS, and LETGS. Animproved atomic line database and a new differential emission measure (DEM)deconvolution method are developed for this purpose. Our new atomic database isbased on the Astrophysical Plasma Emission Database and incorporates improvedcalculations of ionization equilibrium and line emissivities for L-shell ionsof abundant elements using the Flexible Atomic Code. The new DEM deconvolutionmethod uses a Markov Chain Monte-Carlo (MCMC) technique which differs fromexisting MCMC or $\chi^2$-fitting based methods. We analyze the advantages anddisadvantages of each individual instrument in determining the DEM andelemental abundances. We conclude that results from either RGS or HETGS dataalone are not robust enough due to their failure to constrain DEM in sometemperature region or the lack of significant continuum emission in thewavelength band of the spectrometers, and that the combination of HETGS and RGSgives more stringent constraints on the DEM and abundance determinations. Usingthe LETGS data, we show that the recently discovered inconsistencies betweenthe EUV and X-ray lines of Fe XVIII and XIX also exist in more highly chargediron ions, up to Fe XXIII, and that enhanced interstellar absorption due topartially ionized plasma along the Capella line of sight may explain some, butnot all, of these discrepancies.Comment: Accepted in Ap