Bibcode
Burgasser, A. J.; Gillon, Michaël; Melis, Carl; Bowler, Brendan P.; Michelsen, Eric L.; Bardalez Gagliuffi, Daniella; Gelino, Christopher R.; Jehin, E.; Delrez, L.; Manfroid, J.; Blake, Cullen H.
Referencia bibliográfica
The Astronomical Journal, Volume 149, Issue 3, article id. 104, 17 pp. (2015).
Fecha de publicación:
3
2015
Número de citas
49
Número de citas referidas
46
Descripción
We report observations of the recently discovered, nearby late-M dwarf
WISE J072003.20-084651.2. New astrometric measurements obtained with the
TRAPPIST telescope improve the distance measurement to 6.0 ± 1.0
pc and confirm the low tangential velocity (3.5 ± 0.6 km
s‑1) reported by Scholz. Low-resolution optical
spectroscopy indicates a spectral type of M9.5 and prominent Hα
emission (< {{log }10}{{L}Hα
}/{{L}bol}> = ‑4.68 ± 0.06), but no
evidence of subsolar metallicity or Li i absorption. Near-infrared
spectroscopy reveals subtle peculiarities that can be explained by the
presence of a T5 binary companion, and high-resolution laser guide star
adaptive optics imaging reveals a faint (ΔH = 4.1) candidate
source 0\buildrel{\prime\prime}\over{.} 14 (0.8 AU) from the primary.
With high-resolution optical and near-infrared spectroscopy, we measure
a stable radial velocity of +83.8 ± 0.3 km s‑1,
indicative of old disk kinematics and consistent with the angular
separation of the possible companion. We measure a projected rotational
velocity of v sin i = 8.0 ± 0.5 km s‑1 and find
evidence of low-level variabilty (∼1.5%) in a 13 day TRAPPIST light
curve, but cannot robustly constrain the rotational period. We also
observe episodic changes in brightness (1%–2%) and occasional
flare bursts (4%–8%) with a 0.8% duty cycle, and
order-of-magnitude variations in Hα line strength. Combined, these
observations reveal WISE J0720-0846 to be an old, very low-mass binary
whose components straddle the hydrogen burning minimum mass, and whose
primary is a relatively rapid rotator and magnetically active. It is one
of only two known binaries among late M dwarfs within 10 pc of the Sun,
both of which harbor a mid T-type brown dwarf companion. We show that
while this specific configuration is rare (≲1.6% probability),
roughly 25% of binary companions to late-type M dwarfs in the local
population are likely low-temperature T or Y brown dwarfs.
Some of the data presented herein were obtained at the W. M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California and the
National Aeronautics and Space Administration. The Observatory was made
possible by the generous financial support of the W. M. Keck Foundation.