10/1 lunch talk: Magnetic Activity Past the Bottom of the Main Sequence

in Uncategorized
September 30th, 2013

Magnetic Activity Past the Bottom of the Main Sequence

Dr. Peter Williams (CfA)
CAS 500, 12:00 pm, October 1, 2013

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, the formation of the smallest objects, the weather of warm atmospheres, and the properties of turbulent dynamos. This last topic is particularly thorny — while a solar-type shell dynamo cannot operate in the UCD regime, alternative mechanisms are not well-understood, and progress has been hampered by the currently fuzzy observational portrait of UCD magnetic activity. I’ll present several projects that aim to paint a more complete picture, emphasizing recent radio and X-ray observations of a sample of UCDs aimed at clarifying the relationship between rotation and magnetic activity in the ultracool regime. While the existence of a “supersaturation” effect is well supported, the common interpretation of it being caused by centrifugal stripping of coronal plasma is not. We have also performed 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. Many of these observations are made possible by the impressive power of the upgraded Karl G. Jansky Very Large Array.