Signatures of Magnetic Activity in Very Low Mass Stars and Brown Dwarfs. Rachel Osten Hubble Fellows Symposium. Collaborators. Suzanne Hawley University of Washington Tim Bastian NRAO Neill Reid STScI Ray Jayawardhana U. Toronto. Sun M dwarf L dwarf T dwarf Jupiter.
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Hubble Fellows Symposium
Suzanne Hawley University of Washington
Tim Bastian NRAO
Neill Reid STScI
Ray Jayawardhana U. Toronto
Sun M dwarf L dwarf T dwarf Jupiter Brown Dwarfs
levels of emission
Ba 55-87 Mjup
Bb 34-70 Mjup
2MASS 0144-0716 (L5V; Liebert et al. 2003)
Berger 2002; 2MASS 0036+18 (L3.5)
only a handful of detections, all earlier than L4V
Consistent with Ha, X-ray decline in emission with decreasing Teff
Average radio properties
Osten et al. 2006
BDs in Orion t~1 MYr
Preibisch et al. 2005
West et al. 2004
Osten et al. 2006
Radio spectral properties consistent with behavior of earlier spectral type active M stars: magnetic activity present at levels comparable with extrapolations
Osten et al. 2006, ApJ, accepted
Tsuboi et al. 2003
TWA 5B; ~10 Myr old
Fossil magnetic fields probably play a significant role in X-ray activity (Feigelson et al. 2002).
Radio upper limits on all 4 substellar members of the nearest youngest association TW Hydrae (Burgasser & Putman 2005, Osten & Jayawardhana 2006)
Lr/Lx of TWA 5B
compared to field brown dwarfs
Caution: Lx/Lr relationship for active stars still not well understood
Why is this so difficult? Lac (dM3e)
Some possibly important
transient Ha emission out to L5
to date, no X-ray detection of L dwarfs,
radio detections up to L4
is plasma heating to chromospheric temps. easier than to coronal temps?
relative ease/efficiency of particle acceleration vs. plasma heating?
Need large samples with known properties
In-depth investigation of magnetic activity properties to discern differences from active stars