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The Evolution of Angular Momentum of Intermediate Mass Stars: From the Birthline to the Main Sequence

Published online by Cambridge University Press:  26 May 2016

S. C. Wolff ,
S. E. Strom  and
L. A. Hillenbrand
S. C. Wolff
Affiliation:
National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719
S. E. Strom
Affiliation:
National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719
L. A. Hillenbrand
Affiliation:
California Institute of Technology, Dept. of Astronomy, MS 105-24, Pasadena, CA 91125

Abstract

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Measurements of stars in the Orion OB association show that there is a continuous power law relationship between specific angular momentum (J/M) and mass (M) for stars on convective tracks having masses in the range ~0.5 to ~3 M⊙; this power law extends smoothly into the domain of more massive stars on the ZAMS. If we assume that stars are “locked” to circumstellar accretion disks via their magnetic fields until they are deposited on the stellar birthline, we can account for the observed slope and zero point of the power law fit to the upper envelope of the observed J/M vs M distribution.

Pre-main sequence stars with M<2 M⊙ on radiative tracks do not follow the power law relationship. A sharp decrease in J/M with decreasing mass has been recognized for more than 30 years for older field stars, but remarkably is seen already among our Orion sample of stars that are only a few million years old. We show that this break in the power law is a consequence of loss of angular momentum on convective tracks, combined with core-envelope decoupling at the time of the transition from the convective to radiative tracks.

Type
Session 4 Rotation and Stellar Evolution
Information
Symposium - International Astronomical Union , Volume 215: Stellar Rotation , 2004 , pp. 431 - 437
Copyright
Copyright © Astronomical Society of the Pacific 2004 

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