POSTER PAPER 4.19
The Angular Momentum Evolution in M67
J. R. De Medeiros, C. H. F. Melo, L. Pasquini
Institute: Departamento de Fisica, Universidade Federal do Rio Grande do Norte
Institute: Observatoire de Geneve
Institute: European Southern Observatory
Contact Email: renan@dfte.ufrn.br
Abstract:
On the basis of accurate projected rotational velocity vsini for
28 main sequence, turnoff and giant stars, we study the
evolution of the angular momentum in old open cluster M67.
From these data, we show that early main sequence G stars have rotational
velocity two times larger the
Sun, with a possible trend with (B-V) color, in that redder
colors correspond to lower vsini. The stars at the turnoff are
the fastest rotators, with vsini between 6.3 and 7.6
km s-1, while stars just above the turnoff are already
significantly slower. Along the Red Giant Branch rotation
decreases smoothly and for stars redder than (B-V) > 1, only
upper limits can be found, including 4 clump stars. Analyzing the
angular momentum history of 1.2 MSun stars with the help of
theoretical evolutionary tracks, we see that these stars probably
obey different angular momentum evolution laws on the main
sequence and along the Red Giant Branch: while on the main
sequence some extra braking is required, in addition to angular
momentum conservation, along the Red Giant Branch the data are
well represented by the IOmega=C law. Finally, comparing the
rotational velocity of the M67 turnoff stars with their main
sequence progenitors in younger open clusters, we find that
younger clusters show substantially higher rotation rates,
indicating that 1.2 MSun stars do experience main sequence
braking.
Index Keywords: M67; Rotation; Angular Momentum
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Manuscript submitted: 2001-Sep-06
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown,
G. M. Harper, & T. R. Ayres.
Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems,
& The Sun,
© 2003 University of Colorado.