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+401106.8

The 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.