AAS 200th meeting, Albuquerque, NM, June 2002
Session 54. Angular Momentum Evolution of Young Stars
Topical Session Oral, Wednesday, June 5, 2002, 8:30-10:00am, 10:45am-12:30pm, Ruidoso/Pecos

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[54.07] Intermediate Mass Stars: From the Birthline to the Main Sequence

S.C. Wolff, S.E. Strom (NOAO), L.A. Hillenbrand (Caltech)

The observed distribution of stellar rotational velocities of pre-main-sequence (PMS) stars and models of PMS evolution for intermediate mass stars suggest straightforward explanations for the observed relationship between mean surface rotational velocity and stellar mass seen among main-sequence stars: a large fraction of slow rotators among the early B-type stars, a maximum in the average value of vsini among the late B-type stars, and a rapid decrease in the apparent rotational velocity among the A-type stars.

The observed pattern in the B-type stars primarily reflects the differences between stellar radii on the birthline and the final radii on the ZAMS. The decrease in roation in the A-type stars is a consequence of the fact that much of the angular momentum is stored in the radiative core, which is decoupled from the surface convection zone.

Models that posit that stars are locked to circumstellar accretion disks until they are deposited on the birthline can account for both the observed slope and the zero point of the smoothly varying upper envelope of the relationship between specific angular momentum and mass for stars with masses in the range 0.7-10 solar masses.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.