5.3 Lifetimes

Lifetimes of starspots can be determined from long-term observations which are, for instance, provided by continuous photometric data. Hall and Henry (1994 ) analysed several dozen spotted stars and concluded that lifetimes of relatively small spots are proportional to their sizes, which is consistent with sunspot properties. Lifetimes of relatively large spots are possibly limited by a shear of surface differential rotation. On the other hand, large spots causing prominent light curve minima apparently can survive for many years, despite differential rotation, and form centres of activity, or active longitudes (see Section 5.4). This may even be true for pre-main-sequence stars. For instance, based on a comparison of the Doppler image with photometric spot models, Hatzes (1995 ) suggested that the spot on V410 Tau has survived on the stellar surface for about $20 yr$ . Doppler images suggest, however, that these regions often consist of several smaller spots. Lifetimes of those spots are yet to be analysed.