Mg II absolute line profiles for late-type stars and for spatially-resolved solar regions.

Abstract

The authors present the results of a comparison of Mg II h and k line profiles and fluxes for late-type stars observed with IUE and for spatially resolved solar regions observed at comparable resolution by the NRL Spectrograph on Skylab. They show that the spatially resolved solar observations are in good agreement with the disk integrated stellar observations, thus suggesting that different Mg II emission levels observed in stars of similar spectral type are due to different fractions of their surface covered by magnetic regions. The authors confirm that the Mg II stellar fluxes are well correlated with other chromospheric and transition-region fluxes, and show that the spatially resolved solar data obey the same flux-flux relationships as the stellar data with virtually the same slope. They compare some important line diagnostic parameters (k/h, Δk₁, Δk₂, and FWHM of the k line) in disk integrated stellar data and in spatially resolved solar regions, finding no significant discrepancies between the two cases. Finally, the authors discuss the possibility and limitations of using the comparison of solar and stellar Mg II fluxes to infer the fraction of a star's surface covered by magnetic regions.