Rotational velocities of low mass stars in intermediate age open clusters

Abstract

Most previous observational studies of pre-main sequence (PMS) evolution have concentrated on very young, relatively high mass stars. The advantage of that choice is that the program stars are easily identifiable as young via various type of "activity". That characteristic is also a disadvantage, however, since the IR and UV excesses, emission lines, "blue-veiling", and variability make placement of those stars in an HR diagram difficult. In an effort to avoid those difficulties and to extend the observational study of PMS stars to a different portion of parameter space, I have begun a program of study of intermediate age, relatively low mass PMS stars. The primary goals of that program are: (i) to determine the rotational velocity history of low mass stars; (2) to determine the time spread of star formation in open clusters; (3) to derive empirical PMS isochrones for low mass stars. In this paper, I shall emphasize the rotational velocity portion of that program. My collaborators in that work are Lee Hartman, Dave Soderblom, and Neal Burnham.