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 ID: 435493
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Slide1
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 AgeSlide2
Collaborators and FacilitiesAdam Burgasser
Edo Berger
Peter
K. G. WilliamsFred Vrba and the USNO Flagstaff Infrared Parallax TeamKelle CruzStan MetchevNASA award No. NNX13AC18G. WISE, 2MASS, SDSS, IRTF, Kepler, VLA, Gemini, MMT, Keck
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Kepler
MissionSlide4
WISEP J190648.47+401106.8
The L1 dwarf W1906+40 is bright enough to be measured by
Kepler
.Slide5
W1906+40 PropertiesOrdinary L1 dwarf in both optical and near-infrared.
SDSS
g
=22.4, r=20.0, i=17.4. 2MASS J=13.08 Ks=11.77USNO preliminary trigonometric parallax gives 16.35 +/- 0.35 pc.U,V,W = -6, -12, -41 km/sLuminosity is 10-3.67 solar.W1906+40 is magnetically active. Quiscent r
adio emission of 23
m
Jy
.
u
L
u
= (4.5 +/- 0.9) x 1022 erg/s Quiescent but variable Ha emission of 1-10 Angstroms Equivalent WidthRotational velocity v sin i = 11.2 +/- 2.2 km/s
4Slide6
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)Slide7
Five Quarters of Data
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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” variablesSlide8
Evidence of Flares (30 minute cadence)
7Slide9
The Kepler filter is sensitive to blue light, enhancing flare sensitivity
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Gemini
spectra 29 July 2012Slide11
Kepler 1-minute photometry and Emission Lines
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White Light traces heated photosphere, to ~8000K
Longer Lived Heated
Chromospheric
Lines
1
2
3Slide12
Flare Light Curves (1 minute cadence)
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Flare Frequencies
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10
31 erg flare every ~300 hours
One 10
32
erg flare in three months
Long Cadence data ~3 times less frequent. Sensitivity or variability?Slide14
Summary RemarksThis 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.
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