Do stars that lose mass expand or contract? A semianalytical approach

Semianalytic methods are used to determine whether a star of polytropic index n expands or contracts following an insentropic loss of mass. It is found that most stars shrink, including radiative stars which can be approximated by polytropes of index roughly three. However, stars that have a ratio of specific heats gamma only slightly larger than 1 + 1/n do expand if the perturbation of the core density is sufficiently large. For stars that shrink, the fractional change in the radius is not a linear function of the fractional change in mass. Using Lane's theorem, it is shown that a star with gamma = 4/3 cannot lose mass isentropically, although the radius increases if the core density is reduced. 9 references