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X-ray spectra from stellar coronae are reprocessed by the underlyingphotosphere through scattering and photoionization events. While reprocessedX-ray spectra reaching a distant observer are at a flux level of only a fewpercent of that of the corona itself, characteristic lines formed by innershell photoionization of some abundant elements can be significantly stronger.The emergent photospheric spectra are sensitive to the distance and location ofthe fluorescing radiation and can provide diagnostics of coronal geometry andabundance. Here we present Monte Carlo simulations of the photospheric Kalphadoublet arising from quasi-neutral Fe irradiated by a coronal X-ray source.Fluorescent line strengths have been computed as a function of the height ofthe radiation source, the temperature of the ionising X-ray spectrum, and theviewing angle. We also illustrate how the fluorescence efficiencies scale withthe photospheric metallicity and the Fe abundance. Based on the results we makethree comments: (1) fluorescent Fe lines seen from pre-main sequence starsmostly suggest flared disk geometries and/or super-solar disk Fe abundances;(2) the extreme ~1400 mA line observed from a flare on V1486 Ori can beexplained entirely by X-ray fluorescence if the flare itself were partiallyeclipsed by the limb of the star; and (3) the fluorescent Fe line detected bySwift during a large flare on II Peg is consistent with X-ray excitation anddoes not require a collisional ionisation contribution. There is no convincingevidence supporting the energetically challenging explanation of electronimpact excitation for observed stellar Fe Kalpha lines.

X-ray Fluorescent Fe Kalpha Lines from Stellar Photospheres