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

4. Conclusion

New surface gravities of magnetic Bp and Ap stars obtained from the Hipparcos parallaxes, as well as homogeneous spectroscopic gravities, have been used to reconsider how the rotational period of such stars varies with age. The result is entirely consistent with previous works suggesting that field Si stars do not undergo any significant magnetic braking during their life on the Main Sequence; it is also more firmly based than earlier studies made on field Ap stars. Therefore, the slow rotation of these objects must be a property acquired before they arrive on the ZAMS. How this occurs has just been explored by Stepien (1998) but further investigations remain worthwhile.

On the other hand, this study has shown that values obtained from Hipparcos luminosities may be overestimated by up to 0.2 dex for some extreme Ap stars, probably through an overestimate of their . This shows how badly fundamental determinations of are needed for these stars.

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998

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