AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 82. A Stellar and Variable Star Melange
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southwest Exhibit Hall

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[82.08] Rapid Rotation Above and Below the Substellar Boundary

G. Basri (UC Berkeley)

I present the results of a multiyear survey of very low mass stars and brown dwarfs, at high spectral resolution. The echelle spectra were gathered with the HIRES spectrometer at the Keck Observatory. One primary purpose was to determine rotational velocities for many objects of the late M and L spectral classes. Some of these objects are confirmed brown dwarfs, others are stars near the bottom of the main sequence, and some might be either. I show that the initial indication provided by BRI 0021, that such objects tend to be rapidly rotating and display little H-alpha emission, proves to be a common characteristic. There is a general trend to higher rotation velocities as one looks to objects of lower luminosity; the fastest rotator found so far is the brown dwarf Kelu-1 at 80 km/s (which implies a rotation period of about 90 minutes!). The most active object, PC 0025 (which may well be a brown dwarf), is a relatively slow rotator and probably very young. I discuss a possible explanation for these results: the dynamos for these objects are fully turbulent, driven by convection (and therefore indirectly by the object's luminosity), and quenched when the rotational velocities become too fast in comparison to the convective velocities. I thank the NSF for its support through grant AST96-18439.

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