3 M[CLC]s[/CLC] in the Life of β Ceti: Sustained Flare Activity on a Clump Giant Detected by the [ITAL]Extreme Ultraviolet Explorer[/ITAL]

Abstract

A 34 day Extreme Ultraviolet Explorer (EUVE) pointing on the "clump" giant β Ceti (HD 4128; K0 III) recorded a series of striking coronal flare events, reminiscent of a singular outburst seen previously from μ Velorum (HD 93497; G6 III + dF). The recent flaring episode contrasts with a more placid behavior in a 6 day EUVE observation of β Cet 6 years earlier. The average 70-180 Å Deep Survey count rate in the new observation is twice as high, and the 75-150 Å spectrum displays a distinct hardening. The discovery of sustained flare activity on β Cet raises the possibility that such episodes are more common than suspected among the core helium-burning giants and sharpens the puzzle of the survival of magnetic activity beyond helium flash.