Rotation/saturation/dynamos -- Oral Presentation
Stellar Rotation: A Probe of Initial Star-Forming Conditions
Stephen Strom, National Optical Astronomy Observatory
Sidney Wolff (NOAO)
Projected rotational velocities (vsini) have been measured for
B stars in the rich, dense h and chi Persei double cluster along with 7
young (1-7 Myr age) clusters of intermediate density, and compared with
the distribution of rotational velocities for a sample of field stars
having similar ages. In comparison with stars populating the field (and
presumably formed in low density environments), the observed rotation
speeds among stars formed in denser cluster environments are consistently
higher. Moreover, the cluster population lacks the large cohort of slow
(vsini < 50 km/sec) stars found among field B stars. We argue that both
the higher rotation rates and the pattern of rotation speeds that
differentiate B stars in clusters from their field analogs were likely
imprinted during the star formation process rather than a result of
angular momentum evolution. We suggest that these differences may
reflect the effects of the higher accretion rates that theory suggests
are characteristic of regions that give birth to dense clusters, namely,
(1) higher initial rotation speeds; and (2) higher initial radii along
the stellar birth line, resulting in greater spin-up between the birth
line and the ZAMS.