Bibcode
DOI
Berger, E.; Rutledge, R. E.; Reid, I. N.; Bildsten, L.; Gizis, J. E.; Liebert, J.; Martín, E.; Basri, G.; Jayawardhana, R.; Brandeker, A.; Fleming, T. A.; Johns-Krull, C. M.; Giampapa, M. S.; Hawley, S. L.; Schmitt, J. H. M. M.
Referencia bibliográfica
The Astrophysical Journal, Volume 627, Issue 2, pp. 960-973.
Advertised on:
7
2005
Revista
Número de citas
97
Número de citas referidas
89
Descripción
We present the first simultaneous, multiwavelength observations of an L
dwarf, the L3.5 candidate brown dwarf 2MASS J00361617+1821104, conducted
with the Very Large Array, the Chandra X-Ray Observatory, and the Kitt
Peak 4 m telescope. We detect strongly variable and periodic radio
emission (P=3 hr) with a fraction of about 60% circular polarization. No
X-ray emission is detected to a limit of
LX/Lbol<~2×10-5, several
hundred times below the saturation level observed in early M dwarfs.
Similarly, we do not detect Hα emission to a limit of
LHα/Lbol<~2×10-7, the
deepest for any L dwarf observed to date. The ratio of radio to X-ray
luminosity is at least 4 orders of magnitude in excess of that observed
in a wide range of active stars (including M dwarfs), providing the
first direct confirmation that late-M and L dwarfs violate the
radio/X-ray correlation. The radio emission is due to gyrosynchrotron
radiation in a large-scale magnetic field of about 175 G, which is
maintained on timescales longer than 3 yr. The detected 3 hr period may
be due to (1) the orbital motion of a companion at a separation of about
5 stellar radii, similar to the configuration of RS CVn systems, (2) an
equatorial rotation velocity of about 37 km s-1 and an
anchored, long-lived magnetic field, or (3) periodic release of magnetic
stresses in the form of weak flares. In the case of orbital motion, the
magnetic activity may be induced by the companion, possibly explaining
the unusual pattern of activity and the long-lived signal. We conclude
that fully convective stars can maintain a large-scale and stable
magnetic field, but the lack of X-ray and Hα emission indicates
that the atmospheric conditions are markedly different than in
early-type stars and even M dwarfs. Similar observations are therefore
invaluable for probing both the internal and external structure of
low-mass stars and substellar objects, and for providing constraints on
dynamo models.