Astrophysics, abstract
astro-ph/0603194

From: Maria Rosa Zapatero Osorio [view email]

Date: Wed, 8 Mar 2006 12:47:47 GMT (66kb)

Spectroscopic rotational velocities of brown dwarfs

Authors: M. R. Zapatero Osorio, E. L. Martin, H. Bouy, R. Tata, R. Deshpande, R. Wainscoat

Comments: Submitted to ApJ. Will be replaced by the revised version when accepted

We have obtained projected rotation velocities (vsini) of a sample of 19 ultracool dwarfs with spectral types in the interval M6.5-T8 using high-resolution, near-infrared spectra obtained with NIRSPEC and the Keck II telescope. Among our targets there are two young brown dwarfs, two likely field stars, and fifteen likely brown dwarfs (30-72 Mjup) of the solar neighborhood. Our results indicate that both L- and T-type dwarfs are fast rotators in marked contrast to M-type stars. We have derived vsini velocities between <15 and 40 km/s for the T-type objects in our sample, and have found no clear evidence for T dwarfs rotating faster than L dwarfs. However, there is a hint for an increasing lower envelope towards cooler spectral types in the vsini-spectral type diagram. Assuming that field brown dwarfs have a size of 0.09 Rsol, we can place an upper limit of 12.5 h on the equatorial rotation period of T-type brown dwarfs. In addition, we have compared our vsini measurements to spectroscopic rotational velocities of very young brown dwarfs of similar mass available in the literature. The comparison, although model-dependent, suggests that brown dwarfs lose some angular momentum during their contraction; however, their spin down time seems to be significantly longer than that of solar-type to early-M stars.

http://arxiv.org/abs/astro-ph/0603194