2mass J20261584–2943124: An Unresolved L0.5 + T6 Spectral Binary

Gillon

Melis

et al. 2015

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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 (á ñ a L L log H 10 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. 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.

Section: Identification As a Spectral Binarymentioning

confidence: 98%

WISE J072003.20-084651.2: AN OLD AND ACTIVE M9.5 + T5 SPECTRAL BINARY 6 pc FROM THE SUN

Gillon

Melis

et al. 2015

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“…In total, 8 strong and 22 weak candidates were selected, including the previously identified spectral binaries 2MASS J20261584−2943124 (Gelino & Burgasser 2010) candidates overlapped with the index candidates: five as strong and two as weak.…”

Section: Spectral Indicesmentioning

confidence: 99%

SpeX SPECTROSCOPY OF UNRESOLVED VERY LOW MASS BINARIES. II. IDENTIFICATION OF 14 CANDIDATE BINARIES WITH LATE-M/EARLY-L AND T DWARF COMPONENTS

Gagliuffi

Gelino

et al. 2014

ApJ

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127

111

Multiplicity is a key statistic for understanding the formation of very low mass (VLM) stars and brown dwarfs. Currently, the separation distribution of VLM binaries remains poorly constrained at small separations ( 1 AU), leading to uncertainty in the overall binary fraction. We approach this problem by searching for late-M/early-L plus T dwarf spectral binaries whose combined light spectra exhibit distinct peculiarities, allowing for separationindependent identification. We define a set of spectral indices designed to identify these systems, and we use a spectral template fitting method to confirm and characterize spectral binary candidates from a library of 815 spectra from the SpeX Prism Spectral Libraries. We present 11 new binary candidates, confirm 3 previously reported candidates, and rule out 2 previously identified candidates, all with primary and secondary spectral types in the range M7-L7 and T1-T8, respectively. We find that subdwarfs and blue L dwarfs are the primary contaminants in our sample and propose a method for segregating these sources. If confirmed by follow-up observations, these systems may add to the growing list of tight separation binaries, whose orbital properties may yield further insight into brown dwarf formation scenarios.

“…′′ 6 from 2MASS J1315−2649. Images were reduced using custom IDL 10 scripts, as described in Gelino & Burgasser (2010). Figure 5 displays the reduced NIRC2 images from our May observations.…”

Section: Resolved Imaging and Spectroscopymentioning

confidence: 99%

The Hyperactive L Dwarf 2mass J13153094–2649513: Continued Emission and a Brown Dwarf Companion

Sitarski

Gelino

et al. 2011

ApJ

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We report new observations of the unusually active, high proper motion L5e dwarf 2MASS J13153094−2649513. Optical spectroscopy with Magellan/MagE reveals persistent nonthermal emission, with narrow H I Balmer, Na I and K I lines all observed in emission. Low-resolution near-infrared spectroscopy with IRTF/SpeX indicates the presence of a low-temperature companion, which is resolved through multi-epoch laser guide star adaptive optics imaging at Keck. The comoving companion is separated by 338±4 mas, and its relative brightness (∆K s = 5.09±0.10) makes this system the second most extreme flux ratio very low-mass binary identified to date. Resolved near-infrared spectroscopy with Keck/OSIRIS identifies this companion as a T7 dwarf. The absence of Li I absorption in combined-light optical spectroscopy constrains the system age to 0.8-1.0 Gyr, while the system's kinematics and unusually low mass ratio (M 2 /M 1 = 0.3-0.6) suggests that it is even older. A coevality test of the components also indicates an older age, but reveals discrepancies between evolutionary and atmosphere model fits of the secondary which are likely attributable to poor reproduction of its near-infrared spectrum. With a projected separation of 6.6±0.9 AU, the 2MASS J1315−2649 system is too widely separated for mass exchange or magnetospheric interactions to be powering its persistent nonthermal emission. Rather, the emission is probably chromospheric in nature, signaling an inversion in the age-activity relation in which strong magnetic fields are maintained by relatively old and massive ultracool dwarfs.