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Astron. Astrophys. 334, 181-187 (1998)

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Do Si stars undergo any rotational braking? *

P. North

Institut d'Astronomie de l'Université de Lausanne, CH-1290 Chavannes-des-bois, Switzerland

Received 12 December 1997 / Accepted 4 February 1998


The old question of rotational braking of Ap Si stars is revisited on the empirical side, taking advantage of the recent Hipparcos results. Field stars with various evolutionary states are considered, and it is shown that the loose correlation between their rotational period and their surface gravity is entirely compatible with conservation of angular momentum. No evidence is found for any loss of angular momentum on the Main Sequence, which confirms earlier results based on less reliable estimates of surface gravity.

The importance of reliable, fundamental [FORMULA] determinations of Bp and Ap stars is emphasized.

Key words: stars: chemically peculiar – stars: fundamental parameters – stars: individual: HD 124224 – stars: rotation

* Based on data from the ESA Hipparcos satellite

Send offprint requests to: P. North

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998