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1998A&A...335..183Q - Astronomy and Astrophysics, volume 335, 183-198 (1998/7-1)

The rotational velocity of low-mass stars in the Pleiades cluster.

QUELOZ D., ALLAIN S., MERMILLIOD J.-C., BOUVIER J. and MAYOR M.

Abstract (from CDS):

We present new vsin i measurements for 235 low-mass stars in the Pleiades. The differential rotational broadening has been resolved for all the stars in our sample. These results, combined with previously published measurements, provide a complete and unbiased rotation data set for stars in the mass range from 0.6 to 1.2M. Applying a numerical inversion technique on the vsin i distributions, we derive the distributions of equatorial velocities for low-mass Pleiades members. We find that half of the Pleiades dwarfs with a mass between 0.6 to 1M have rotation rates lower than 10km/s. Comparison of the rotational distributions of low-mass members between IC 2602/2391 (≃35Myr) and the Pleiades (≃100Myr) suggests that G dwarfs behave like solid-bodies and follow Skumanich's law during this time span. However, comparison between Pleiades and older clusters -M34 (≃200Myr) and Hyades (≃600Myr)- indicates that the braking of slow rotators on the early main sequence is weaker than predicted by an asymptotical Skumanich's law. This strongly supports the view that angular momentum tapped in the radiative core of slow rotators on the zero age main sequence (ZAMS) resurfaces into the convective envelope between Pleiades and Hyades age. For the G-dwarfs, we derive a characteristic coupling time scale between the core and the envelope of about 100-200Myr, which accounts for the observed evolution of surface rotation from the ZAMS to the Hyades. The relationship between rotation and coronal activity in the Pleiades is in agreement with previous observations in other clusters and field stars. We show that the Rossby diagram provides an excellent description of the X-ray activity for all stars in the mass domain studied. The Pleiades data for slow and moderate rotators fills the gap between the X-ray-rotation correlation found for slow rotators and the X-ray saturation plateau'' observed for young fast rotators. The transition between increasing X-ray flux with rotation and X-ray saturation is observed at log(P/τ)=0.8±0.1. These results strengthen the hypothesis that the saturation'' of the angular momentum loss process depends on the stellar mass.