Stellar rotation in the Hyades and Praesepe: gyrochronology and braking timescale

Delorme, P.; Collier Cameron, A.; Hebb, L.; Rostron, J.; Lister, T. A.; Norton, A. J.; Pollacco, D. and West, R. G. (2010). Stellar rotation in the Hyades and Praesepe: gyrochronology and braking timescale. In: SF2A-2010: Proceedings of the Annual Meeting of the French Society of Astronomy and Astrophysics, 21-24 Jun 2010, Marseille, France.


We present the results of photometric surveys for stellar rotation in the Hyades and in Praesepe, using data obtained as part of the SuperWASP exoplanetary transit-search programme. We determined accurate rotation periods for more than 120 sources whose cluster membership was confirmed by common proper motion and colour-magnitude fits to the clusters' isochrones. This allowed us to determine the effect of magnetic braking on a wide range of spectral types for expected ages of ˜ 600 Myr for the Hyades and Praesepe. Both clusters show a tight and nearly linear relation between J-Ks colour and rotation period in the F,G and K spectral range. This confirms that loss of angular momentum was significant enough that stars with strongly different initial rotation rates have converged to the same rotation period for a given mass, by the age of Hyades and Praesepe. In the case of the Hyades our colour-period sequence extends well into the M dwarf regime and shows a steep increase in the scatter of the colour-period relation, with identification of numerous rapid rotators from ˜0.5 M_ȯ down to the lowest masses probed by our survey(˜0.25 M_ȯ). This provides crucial constraints on the rotational braking timescales and further clears the way to use gyrochronology as an accurate age measurement tool for main-sequence stars.

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