Stellar rotation in the Hyades and Praesepe: gyrochronology and braking time-scale

Delorme, P.; Cameron, A. Collier; Hebb, L.; Rostron, J.; Lister, T. A.; Norton, A. J.; Pollacco, D. and West, R. G. (2011). Stellar rotation in the Hyades and Praesepe: gyrochronology and braking time-scale. Monthly Notices of the Royal Astronomical Society, 413(3) pp. 2218–2234.

DOI: https://doi.org/10.1111/j.1365-2966.2011.18299.x

Abstract

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-K_s 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 ages 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_ʘ down to the lowest masses probed by our survey (~0.25 M_ʘ). This provides crucial constraints on the rotational braking time-scales and further clears the way to use gyrochronology as an accurate age measurement tool for main-sequence stars.

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