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L. M. Rebull (SIRTF Science Center), S. C. Wolff, S. E. Strom (NOAO)
To investigate what happens to angular momentum during the earliest observable phases of stellar evolution, we combined our measurements of periods (P), projected rotational velocities (v \sin i), and supporting data on K5-M2 stars (corresponding to masses 0.25 to 1 M\sun) with those published in the literature for the Orion Nebula Cluster and environs, \rho Oph, TW Hydra, Taurus-Auriga, NGC 2264, Chamaeleon, Lupus, and \eta Cha. We combine these measures of rotation with the derived values of stellar R (as determined from L\rm bol and T\rm eff) to compare the data with two extreme scenarios for the evolution of PMS angular momenta: conservation of stellar angular velocity and conservation of stellar angular momentum. Both the P and v \sin i datasets suggest that a significant fraction of all PMS stars must evolve at nearly constant angular velocity during the first ~3-5 million years after they begin their evolution down convective tracks. Hence, the angular momenta of a significant fraction of PMS stars must be tightly regulated during the first few million years after they first become observable. This result seems surprising at first glance, because observations of young main sequence stars reveal a population (30-40%) of rapidly rotating stars that must begin to spin up at ages t << 5 Myr. To determine whether these apparently contradictory results are reconcilable, we make use of simple simulations and find that a modest population (30-40%) of PMS stars could in fact be released within the first 1 Myr and still produce period distributions statistically consistent with the observed data.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.