HD 61396: An unusual mass-transfer RS CVn binary

HD 61396 has been identified as an X-ray and radio source and has shown Hα emission and photometric variability which have marked it out as an RS CVn star. Although it has been termed an RS CVn binary, hard evidence of its duplicity has been lacking. It is now shown to be a double-lined binary consisting of two giant stars, probably of almost equal size and luminosity but with a mass ratio of more than eight to one, in a 34-day orbit that is circular or very nearly so. Mass transfer is probably still continuing. We have not been able to produce a satisfactory evolutionary model.