Starspots on flare stars

Sizes of starspots on flare stars can be derived from the author's convection-cell hypothesis. The sizes are in fair agreement with those observed on YY Gem, CC Eri, and BY Dra by Bopp and Evans. The hypothesis predicts that periodic brightness variations due to starspots are restricted to stars brighter than a critical absolute visual magnitude. A convective model of a starspot on YY Gem has been computed, assuming that the missing flux is in the form of Alfve'n waves. It is found that the surface field must exceed 10 gauss, and is probably less than about 3 x 10 gauss. With a surface field of 2 x 10 gauss, the effective temperature of the spot is in the range Te = K, depending on the field gradient. These figures are to be compared with Te = 2000 K estimated from observations by Bopp and Evans. Efficient dynamo action is shown to be a possible mechanism for generating such large surface fields. There is a possibility that tidal effects may influence starspot formation. Subject headings: flare stars - hydromagnetics - late-type stars - magnetic stars