Sean P. Matt, Giovanni Pinzon, Thomas P. Greene, Ralph E. Pudritz
We present a model for the rotational evolution of a young, solar-mass star
interacting magnetically with an accretion disk. As in a previous paper (Paper
I), the model includes changes in the star's mass and radius as it descends the
Hayashi track, a decreasing accretion rate, and a prescription for the angular
momentum transfer between the star and disk. Paper I concluded that, for the
relatively strong magnetic coupling expected in real systems, additional
processes are necessary to explain the existence of slowly rotating
pre-main-sequence stars. In the present paper, we extend the stellar spin model
to include the effect of a spin-down torque that arises from an
accretion-powered stellar wind. For a range of magnetic field strengths,
accretion rates, initial spin rates, and mass outflow rates, the modeled stars
exhibit rotation periods within the range of 1--10 days in the age range of
1--3 Myr. This range coincides with the bulk of the observed rotation periods,
with the slow rotators corresponding to stars with the lowest accretion rates,
strongest magnetic fields, and/or highest stellar wind mass outflow rates. We
also make a direct, quantitative comparison between the accretion-powered
stellar wind scenario and the two types of disk-locking models (namely the
X-wind and Ghosh & Lamb type models) and identify some remaining theoretical
issues for understanding young star spins.
View original:
http://arxiv.org/abs/1111.6407
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