First Detection of a Strong Magnetic Field on a Bursty Brown Dwarf: Puzzle Solved

Journal Article · Wed Sep 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA866B· OSTI ID:22875787

Berdyugina, S. V.; Harrington, D. M.; Kuzmychov, O. ^[1]; Kuhn, J. R. ^[2]; Hallinan, G. ^[3]; Kowalski, A. F. ^[4]

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1. Kiepenheuer Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg (Germany)
2. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, 96822-1897 HI (United States)
3. California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
4. Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, 2000 Colorado Avenue, Boulder, CO 80305 (United States)

We report the first direct detection of a strong, 5 kG magnetic field on the surface of an active brown dwarf. LSR J1835+3259 is an M8.5 dwarf exhibiting transient radio and optical emission bursts modulated by fast rotation. We have detected the surface magnetic field as circularly polarized signatures in the 819 nm sodium lines when an active emission region faced the Earth. Modeling Stokes profiles of these lines reveals the effective temperature of 2800 K and log gravity acceleration of 4.5. These parameters place LSR J1835+3259 on evolutionary tracks as a young brown dwarf with the mass of 55±4M{sub J} and age of 22 ± 4 Myr. Its magnetic field is at least 5.1 kG and covers at least 11% of the visible hemisphere. The active region topology recovered using line profile inversions comprises hot plasma loops with a vertical stratification of optical and radio emission sources. These loops rotate with the dwarf in and out of view causing periodic emission bursts. The magnetic field is detected at the base of the loops. This is the first time that we can quantitatively associate brown dwarf non-thermal bursts with a strong, 5 kG surface magnetic field and solve the puzzle of their driving mechanism. This is also the coolest known dwarf with such a strong surface magnetic field. The young age of LSR J1835+3259 implies that it may still maintain a disk, which may facilitate bursts via magnetospheric accretion, like in higher-mass T Tau-type stars. Our results pave a path toward magnetic studies of brown dwarfs and hot Jupiters.

• OSTI ID: 22875787
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 847; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPUTERIZED SIMULATION
DETECTION
DWARF STARS
EMISSION
GRAVITATION
HOT PLASMA
MAGNETIC FIELDS
MASS
PERIODICITY
POLARIZATION
ROTATION
SODIUM
STRATIFICATION
SURFACES