The Distant Future of Solar Activity: A Case Study of beta Hydri. II. Chromospheric Activity and Variability

Abstract

A detailed comparison of the present sun with the very old star Beta Hyi (G2 IV) is presented in order to study the secular evolution of solar-type chromospheres, with emphasis placed on chromospheric features and their time variability. High-resolution Ca II H and K profiles show the emission to be about half that for the sun, but with the same sense of violet-red asymmetry. The emission's wavelength width is slightly broader, consistent with the Wilson-Bappu relation for this slightly more luminous star. Mg II h and k profiles also exhibit an emission weaker than the sun, but with the opposite sense of asymmetry, probably altered by absorption in a nearby interstellar cloud. The emission variations are small and are characterized by smooth and systematic change in the line profiles from year to year, suggesting continuous changes in the chromospheric structure, rather than the sudden emergence of growth of active regions.