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Angular momentum loss and stellar spin-down in magnetic massive stars

Published online by Cambridge University Press:  01 November 2008

Asif ud-Doula
Affiliation:
Department of Physics, SUNY-Morrisville State College, Morrisville, NY 13408, USA e-mail: uddoula@morrisville.edu
Stanley P. Owocki
Affiliation:
Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
Richard H.D. Townsend
Affiliation:
Department of Physics, University of Wisconsin-Madison, Madison, WI 53706, USA
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Abstract

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We examine the angular momentum loss and associated rotational spin-down for magnetic hot stars with a line-driven stellar wind and a rotation-aligned dipole magnetic field. Our analysis here is based on our previous 2-D numerical MHD simulation study that examines the interplay among wind, field, and rotation as a function of two dimensionless parameters, W(=Vrot/Vorb) and ‘wind magnetic confinement’, η∗ defined below. We compare and contrast the 2-D, time variable angular momentum loss of this dipole model of a hot-star wind with the classical 1-D steady-state analysis by Weber and Davis (WD), who used an idealized monopole field to model the angular momentum loss in the solar wind. Despite the differences, we find that the total angular momentum loss averaged over both solid angle and time follows closely the general WD scaling ~ ΩR2A. The key distinction is that for a dipole field Alfvèn radius RA is significantly smaller than for the monopole field WD used in their analyses. This leads to a slower stellar spin-down for the dipole field with typical spin-down times of order 1 Myr for several known magnetic massive stars.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2009

References

ud-Doula, A. & Owocki, S. P., 2002, ApJ 576, 413CrossRefGoogle Scholar
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ud-Doula, A., Owocki, S. P., & Townsend, R. H. D., 2008, MNRAS, in pressGoogle Scholar
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