Spots and White Light Flares
in an L dwarf
John Gizis
Department of Physics and Astronomy
University of Delaware
May 24, 2013
@Brown Dwarfs Come of Age
Collaborators and Facilities
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Adam Burgasser
Edo Berger
Peter K. G. Williams
Fred Vrba and the USNO Flagstaff Infrared Parallax Team
Kelle Cruz
Stan Metchev
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NASA award No. NNX13AC18G.
WISE, 2MASS, SDSS, IRTF, Kepler, VLA, Gemini, MMT, Keck
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WISEP J190648.47+401106.8
The L1 dwarf W1906+40 is bright
enough to be measured by Kepler.
W1906+40 Properties
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Ordinary L1 dwarf in both optical and near-infrared.
SDSS g=22.4, r=20.0, i=17.4. 2MASS J=13.08 Ks=11.77
USNO preliminary trigonometric parallax gives 16.35 +/- 0.35 pc.
U,V,W = -6, -12, -41 km/s
Luminosity is 10-3.67 solar.
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W1906+40 is magnetically active.
Quiscent radio emission of 23 mJy.
u Lu = (4.5 +/- 0.9) x 1022 erg/s
Quiescent but variable Ha emission of 1-10 Angstroms Equivalent Width
Rotational velocity v sin i = 11.2 +/- 2.2 km/s
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This L dwarf may be modeled by a single dark
spot with P=8.9 hours, or some more
complicated pattern
Dark spot not unlike those seen in Kepler M dwarfs (GO 030021)
Five Quarters of
Data
The phase and amplitude are
largely consistent for 1.25
years
Previous I-band studies
reported non-periodic
variations on short timescales,
and inconsistencies between
observing runs.
W1906+40 is much different
than the late-L/T “weather”
variables
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Evidence of Flares (30 minute cadence)
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The Kepler filter is sensitive to blue light,
enhancing flare sensitivity
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Gemini spectra 29 July 2012
Kepler 1-minute photometry and Emission
Lines
White Light traces heated
photosphere, to ~8000K
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Longer Lived Heated
Chromospheric Lines
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Flare Light Curves (1 minute cadence)
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Flare Frequencies
One 1032 erg flare in three months
1031 erg flare every
~300 hours
Long Cadence data ~3 times
less frequent. Sensitivity or
variability?
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Summary Remarks
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This L1 dwarf shows quiescent H alpha and radio emission
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For the first time, we have seen white light flares in an L dwarf (although
similar flares have been seen in M7-M9 dwarfs.)
These flares require heating of both the chromosphere and the
photosphere, to >6000K. Very similar to dMe flares.
The frequency of these flares is much less than in M dwarfs with similar
rotation period, but are as frequent as in the Sun.
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Large magnetic starspots(s) seem likely. The cloud variations seen in lateL/T-dwarfs don’t stay consistent for very long.
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