Rotational Velocities and Chromospheric/Coronal Activity of Low‐Mass Stars in the Young Open Clusters IC 2391 and IC 2602

We have obtained high-resolution, moderate signal-to-noise ratio spectra for approximately 80 candidate low-mass members of the nearby, very young open clusters IC 2391 and IC 2602. Most of the stars observed are conrmed as cluster members based on a combination of photometric and spectroscopic criteria. We provide radial velocities, rotational velocities, and Ha equivalent widths for these stars. From comparison to theoretical premain-sequence (PMS) evolutionary isochrones from DAntona and Mazzitelli, we derive an estimated age of the two clusters of D25 Myr. By contrast, the usually quoted upper main-sequence turno age for the clusters is D35 Myr. We do not believe that this provides evidence for noncoeval star formation within these clusters, but rather that the best age estimate for them given the uncertainties is D30 ^5 Myr. In principle, the scatter of stars about the PMS isochrone provides a measure of the age spread among the low-mass stars in these clusters ; however, with the data presently available, we are able to derive only a relatively uninteresting upper limit for an age spread of order 20 Myr.