We analyze rotation velocities and chromospheric (H-alpha) activity, derived from multi-year, high-resolution spectra, in 56 mid-M to L dwarfs. Rotational velocities are found to increase from mid-M to L. This is consistent with a lengthening of spin-down timescale with later type, though in the L types the trend may also be a function of stellar age. From M5 to M8.5, a saturation-type rotation-activity relation is seen, similar to that in earlier types. However, the saturation velocity in our case is much higher, at about 12 km/s. A sharp drop in activity is observed at about M9, with later types showing little or no H-alpha emission, in spite of rapid rotation. This may be due to the very high resistivities in the predominantly neutral atmospheres of these cool objects.
@article{arxiv.astro-ph/0201455,
title = {Rotation and Activity in Mid-M to L Dwarfs},
author = {Subhanjoy Mohanty and Gibor Basri},
journal= {arXiv preprint arXiv:astro-ph/0201455},
year = {2009}
}
Comments
7 pages, 4 figures, to be published in proceedings of 'Cool Stars and the Sun 12'