Hα region spectroscopy of the RS CVn system HR 5110

High-resolution (0.3 A) echelle spectra covering all orbital phases of the bright RS CVn binary HR 5110 have been obtained for the Hα region. Lines from the cool secondary (other than Ca II H and K) have been detected for the first time, providing new mass and light ratios: M2/M1 = 0.54 and F2/F1 = 0.20. Effective temperatures of 6750 and 4700 K for the primary and secondary, respectively, have been estimated from the line spectrum. A composite comparison spectrum was subtracted from the weak Hα absorption profile, revealing strong, variable Hα emission with two components: a narrow and steady emission peak and a variable and extremely broad component. Stark broadening in a dense chromosphere of the K star can explain the broad component, while the narrow peak appears to come from an unusually bright Hα core in the F star. (author)