Optical Studies of X-ray Peculiar Chromospherically Active Stars

Abstract

Late-type stars (F, G, K, M), also called cool stars show activity phenomenon that appear analogous to features observed on the Sun. Activity and variability in these stars are often explained in terms of processes producing magnetically active regions distributed across the stellar surface. These are indicative of dynamo action within the convective envelopes of these stars. However, there are vast differences regarding the strengths and lifetimes of these structures compared to the solar features. By studying the stellar activity more closely we can investigate how dynamo mechanism are affected by differences in stellar parameters (such as age, mass, rotation etc). This in turn gives us further insight into the evolution of the solar dynamo. On learning more about the magnetic configurations of these stellar atmosphere we can also evaluate how important the magnetic activity is in determining the stellar evolution. Various observational characteristics of stellar activity in cool stars are outlined in this chapter with a particular emphasis on the types/phenomenon that are observed in their atmospheres.