CfA OIR Division Lunch Talks
Wednesday, April 17, 2013, 11:00 am, Pratt Conference Room

Magnetic Activity Past the Bottom of the Main Sequence

Peter Williams (CfA)

Very low-mass stars and brown dwarfs ("ultracool dwarfs": UCDs) bridge the stellar and planetary regimes and can be used to attack a variety of astrophysical puzzles, including the enrichment history of the Milky Way, how the smallest objects form, the weather of warm atmospheres, and the properties of turbulent dynamos. This last topic is particularly thorny -- while it is agreed that the solar dynamo cannot operate in the UCD regime, alternative mechanisms are not well-understood, and progress has been hampered by the currently fuzzy portrait of UCD magnetic activity. I'll present recent observations that aim to paint a more complete picture. These include detailed studies of several unusual sources, including the first radio-emitting T dwarf, an L dwarf in the Kepler field of view, and a radio-bright M dwarf with an exceptionally flat spectrum. I'll also examine trends in activity tracers observed in the overall UCD population, including mounting evidence for a "supersaturation" effect in the UCD X-ray rotation/activity relationship. Many of these observations are made possible by the impressive power of the upgraded Karl G. Jansky Very Large Array.