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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. Adam Burgasser Edo Berger Peter K. G. Williams - PowerPoint PPT Presentation
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Spots and White Light Flares in an L dwarf
John GizisDepartment of Physics and Astronomy
University of DelawareMay 24, 2013
@Brown Dwarfs Come of Age
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Collaborators and Facilities
• Adam Burgasser• Edo Berger• Peter K. G. Williams• Fred Vrba and the USNO Flagstaff Infrared Parallax Team• Kelle Cruz• Stan Metchev
• NASA award No. NNX13AC18G. • WISE, 2MASS, SDSS, IRTF, Kepler, VLA, Gemini, MMT, Keck
Kepler Mission
WISEP J190648.47+401106.8The L1 dwarf W1906+40 is bright enough to be measured by Kepler.
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W1906+40 Properties
• 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.
• 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
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)
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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
Gemini spectra 29 July 2012
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Kepler 1-minute photometry and Emission Lines
White Light traces heated photosphere, to ~8000K
Longer Lived Heated Chromospheric Lines
1 2 3
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Flare Light Curves (1 minute cadence)
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Flare Frequencies
1031 erg flare every ~300 hours
One 1032 erg flare in three months
Long Cadence data ~3 times less frequent. Sensitivity or
variability?
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Summary Remarks
• This L1 dwarf shows quiescent H alpha and radio emission.• Large magnetic starspots(s) seem likely. The cloud variations seen
in late-L/T-dwarfs don’t stay consistent for very long.
• 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.