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On the Loss of Angular Momentum from Stars in the Pre-Main Sequence Phase

Published online by Cambridge University Press:  12 April 2016

Isao Okamoto
Isao Okamoto*
Affiliation:
The international Latitude Observatory of Mizusawa, Iwate, Japan

Abstract

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The braking of stellar rotation in the wholly convective phase in the pre-main sequence is numerically discussed. The structure of stars in that phase is expressed by a rotating polytrope with an index of 1.5 and the Schatzman-type mechanism is used as the means of loss of angular momentum. The magnetic energy is assumed to change with evolution as H02/8π(R/R0)s, where H0 and R0 are initial magnetic field and radius, and s is a free parameter. The changes of angular momentum, rotational velocity, etc. with contraction are calculated from the initial state, which is taken to be the state when the stars flared up to the Helmholtz-Kelvin contraction. It is shown that the exponent s must be in the range from – 1 to – 3 so that the stars with adequate strength of the initial magnetic field may lose almost all of their angular momenta in a suitable rate if they are initially in the state of rotational instability.

Stellar rotation from the time of star formation to the main sequence stage is discussed. Also, the formation of the solar system and other planetary systems is discussed, with respect to the braking.

Type
Part I / The Effects of Rotation on Stellar Interiors and Evolution
Information
International Astronomical Union Colloquium , Volume 4: Stellar Rotation , 1970 , pp. 73 - 81
Copyright
Copyright © Reidel 1970

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