The Changing Period of R Hya

Abstract

We discuss the period evolution of the Mira variable R Hya. We show, using observations dating back to 1662, that it has evolved from a stable 500-day period to a stable 380-day period. The onset of the period evolution coincided with a sharp decline in mass-loss rate. We suggest that mass-loss fluctuations over a period of a few hundred years may be common in Miras, and relate to a non-linear pulsation instability.