III. Velocity distributions
GEPI/CNRS UMR 8111, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon Cedex, France e-mail: email@example.com
2 CNRS, Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
Accepted: 22 October 2006
Aims.A sample of of B9 to F2-type main sequence single stars has been built from highly homogeneous parameters determined for a large sample cleansed of objects presenting the Am and Ap phenomenon as well as of all known binaries. The aim is to study the distributions of rotational velocities in the mass range of A-type stars for normal single objects.
Methods.Robust statistical methods are used to rectify the distributions for the projection effect and the error distribution. The equatorial velocity distributions are obtained for about 1100 stars divided in six groups defined by the spectral type, under the assumption of randomly orientated rotational axes.
Results.We show that late B and early A-type main-sequence stars have genuine bimodal distributions of true equatorial rotational velocities probably due to angular momentum loss and redistribution that the star underwent before reaching the main sequence. A striking lack of slow rotators is noticed among intermediate and late A-type stars.
Key words: stars: early-type / stars: rotation
© ESO, 2007