Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...294..469k&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 294, no. 2, p. 469-487
Astronomy and Astrophysics
Astrophysics
110
Angular Velocity, Main Sequence Stars, Pre-Main Sequence Stars, Stellar Evolution, Stellar Rotation, Velocity Distribution, Accretion Disks, Angular Momentum, Stellar Magnetic Fields, Stellar Mass Ejection
Scientific paper
We investigate how the distribution of rotational velocities for late-type stars or a given mass evolves with age, both before and during residence on the main sequence. Starting from an age approximately 106 years, an assumed pre-main sequence rotational velocity/period distribution is evolved forward in time using the model described by MacGregor & Brenner (1991) to trace the rotational histories of single, constituent stars. This model treats: (1) stellar angular momentum loss as a result of the torque applied to the convection zone by a magnetically coupled wind; (2) angular momentum transport from the radiative interior to the convective envelope in response to the rotational deceleration of the stellar surface layers; and (3), angular momentum redistribution associated with changes in internal structure during the process of contraction to the main sequence. We ascertain how the evolution of a specified, initial rotational velocity/period distribution is affected by such things as: (1) the dependence of the coronal magnetic field strength on rotation rate through a prescribed, phenomenological dynamo relation; (2) the magnitude of the timescale tauc characterizing the transfer of angular momentum from the core to the envelope; (3) differences in the details and duration of pre-main sequence structural evolution for stars with masses in the range 0.8 less than or equal to M*/solar mass less than or equal to 1.0; and (4), the exchange of angular momentum between a star and a surrounding, magnetized accretion disk during the first few million years of pre-main sequence evolution following the development of a radiative core. The results of this extensive parameter study are compared with the distributions derived from measurements of rotational velocities of solar-type stars in open clusters with known ages. Starting from an initial distribution compiled from observations of rotation among T Tauri stars, we find that reasonable agreement with the distribution evolution inferred from cluster observations is obtained for some cases.
Charbonneau Patrick
Keppens Rony
MacGregor Keith B.
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