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Lane, C,Hallinan, G,Zavala, RT,Butler, RF,Boyle, RP,Bourke, S,Antonova, A,Doyle, JG,Vrba, FJ,Golden, A
2007
October
Astrophysical Journal
Rotational modulation of M/L dwarfs due to magnetic spots
Published
()
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TIME-SERIES ANALYSIS ULTRACOOL DWARF SUBSTELLAR BOUNDARY RADIO-EMISSION BROWN DWARFS COOL DWARFS SPACED DATA VARIABILITY ATMOSPHERES EVOLUTION
668
163
166
We find periodic I- band variability in two ultracool dwarfs, TVLM 513- 46546 and 2MASS J00361617 + 1821104, on either side of the M/L dwarf boundary. Both of these targets are short- period radio transients, with the detected I- band periods matching those found at radio wavelengths (P=1.96 hr for TVLM 513-46546 and P=3 hr for 2MASS J00361617 + 1821104). We attribute the detected I- band periodicities to the periods of rotation of the dwarfs, supported by radius estimates and measured values for the objects. Based on the detected period of rotation v sin i of TVLM 513- 46546 ( M9) in the I band, along with confirmation of strong magnetic fields from recent radio observations, we argue for magnetically induced spots as the cause of this periodic variability. The I- band rotational modulation of the L3.5 dwarf 2MASS J00361617 + 1821104 appeared to vary in amplitude with time. We conclude that the most likely cause of the I- band variability for this object is magnetic spots, possibly coupled with time-evolving features such as dust clouds.
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