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Paper: New Rotational Velocities of M Dwarfs in the Pleiades and Hyades
Volume: 154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop
Page: 1331
Authors: Stauffer, John; Jones, Burton; Fischer, Debra; Krishnamurthi, Anita; Pinsonneault, Marc; Terndrup, Donald; Wolff, Sidney
Abstract: We have used the KPNO 4m and the Keck I telescopes to obtain spectroscopic rotational velocities of M dwarf members of the Pleiades and Hyades in order to define better the angular momentum evolutionary history of low mass stars. The new data include 60 Pleiades members with 8.5 < M_V < 11.5, and 20 Hyades members with 12.6 < M_V < 15.6. Some empirical aspects of our analysis of these spectra include: a) fainter than M_V ~10.5, apparently all Pleiades members have rotational velocities above v_rot ~6 km s^{-1}, corresponding to rotational periods less than about 3 days. The range in rotational velocity at a given color decreases with decreasing mass, going from a factor of more than 15 for early K dwarfs to only a factor of 2 or 3 for late M dwarfs; b) in terms of their angular rotational velocities, the most rapidly rotating stars in the Pleiades are M dwarfs, with inferred periods ranging from ~4 to ~8 hours; c) even by the age of the Hyades, the very low mass M dwarfs still rotate relatively rapidly, with spectroscopic rotational velocities up to about 35 km s^{-1}, and hence inferred rotational periods as short as about 8 hours. The late M dwarfs appear to decrease their rotation rate by perhaps a factor of two between the age of the Pleiades and the age of the Hyades. We will discuss the implications of these observations using new rotational velocity evolution models for low mass stars constructed using an updated version of the Yale evolutionary code.
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