Periodic Radio Emission from the M7 Dwarf 2MASS J13142039+1320011: Implications for the Magnetic Field Topology
- Autor(en)
- M. McLean, E. Berger, J. Irwin, J. Forbrich, A. Reiners
- Abstrakt
We present multi-epoch radio and optical observations of the M7 dwarf2MASS J13142039+1320011. We detect a ~1 mJy source at 1.43, 4.86, 8.46,and 22.5 GHz, making it the most luminous radio emission over the widest frequency range detected from an ultracool dwarf to date. A 10 hr VeryLarge Array observation reveals that the radio emission varies sinusoidally with a period of 3.89 ± 0.05 hr, and an amplitude of≈30% at 4.86 GHz and ≈20% at 8.46 GHz. The periodicity is also seen in circular polarization, where at 4.86 GHz the polarization reverses helicity from left- to right-handed in phase with the total intensity. An archival detection in the Faint Images of the Radio Sky atTwenty Centimeters survey indicates that the radio emission has beenstable for at least a decade. We also detect periodic photometric variability in several optical filters with a period of 3.79 hr andmeasure a rotation velocity of vsin i = 45 ± 5 km s-1,in good agreement with the radio and optical periods. The subtle difference in radio and optical periods may be due to differential rotation, with ΔΩ ≈ 1 rad day-1 between theequation and poles. The period and rotation velocity allow us to place a lower limit on the radius of the source of >~ 0.13R sun,about 30% larger than theoretical expectations. The properties of theradio emission can be explained with a simple model of a magnetic dipolemisaligned relative to the stellar rotation axis, with the sinusoidal variations and helicity reversal due to the rotation of the magnetic poles relative to our line of sight. The long-term stability of the radio emission indicates that the magnetic field (and hence the dynamo) is stable on a much longer timescale than the convective turnover timeof ~0.2 yr. If the radio emission is due to gyrosynchrotron emission the inferred magnetic field strength is ~0.1 kG, while the electroncyclotron maser process requires a field of at least 8 kG.
- Organisation(en)
- Institut für Astrophysik
- Externe Organisation(en)
- Harvard-Smithsonian Center for Astrophysics, Georg-August-Universität Göttingen
- Journal
- The Astrophysical Journal: an international review of astronomy and astronomical physics
- Band
- 741
- Anzahl der Seiten
- 8
- ISSN
- 0004-637X
- DOI
- https://doi.org/10.1088/0004-637X/741/1/27
- Publikationsdatum
- 11-2011
- Peer-reviewed
- Ja
- ÖFOS 2012
- 103004 Astrophysik
- Schlagwörter
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/f6e689f8-ae74-4d56-9ecf-3d90360c83ae