Astrophys. J., 778, 36 (2013/November-3)
Discovery of a visual T-dwarf triple system and binarity at the L/T transition.
RADIGAN J., JAYAWARDHANA R., LAFRENIERE D., DUPUY T.J., LIU M.C. and SCHOLZ A.
Abstract (from CDS):
We present new high contrast imaging of eight L/T transition brown dwarfs (BDs) using the NIRC2 camera on the Keck II telescope. One of our targets, the T3.5 dwarf 2MASS J08381155+1511155, was resolved into a hierarchal triple with projected separations of 2.5±0.5 AU and 27±5 AU for the BC and A(BC) components, respectively. Resolved OSIRIS spectroscopy of the A(BC) components confirms that all system members are T dwarfs. The system therefore constitutes the first triple T-dwarf system ever reported. Using resolved photometry to model the integrated-light spectrum, we infer spectral types of T3±1, T3±1, and T4.5±1 for the A, B, and C components, respectively. The uniformly brighter primary has a bluer J - Ks color than the next faintest component, which may reflect a sensitive dependence of the L/T transition temperature on gravity, or alternatively divergent cloud properties among components. Relying on empirical trends and evolutionary models we infer a total system mass of 0.034-0.104 M☉ for the BC components at ages of 0.3-3 Gyr, which would imply a period of 12-21 yr assuming the system semimajor axis to be similar to its projection. We also infer differences in effective temperatures and surface gravities between components of no more than ∼150 K and ∼0.1 dex. Given the similar physical properties of the components, the 2M0838+15 system provides a controlled sample for constraining the relative roles of effective temperature, surface gravity, and dust clouds in the poorly understood L/T transition regime. For an age of 3 Gyr we estimate a binding energy of ∼20 x1041 erg for the wide A(BC) pair, which falls above the empirical minimum found for typical BD binaries, and suggests that the system may have been able to survive a dynamical ejection during formation. Combining our imaging survey results with previous work we find an observed binary fraction of 4/18 or 22–8+10% for unresolved spectral types of L9-T4 at separations ≳ 0.''1. This translates into a volume-corrected frequency of 13–6+7%, which is similar to values of ∼9%-12% reported outside the transition. Our reported L/T transition binary fraction is roughly twice as large as the binary fraction of an equivalent L9-T4 sample selected from primary rather than unresolved spectral types (6–4+6%); however, this increase is not yet statistically significant and a larger sample is required to settle the issue.
binaries: visual - brown dwarfs - stars: individual: 2MASS J08381155+1511155
View the references in ADS
To bookmark this query, right click on this link: simbad:2013ApJ...778...36R and select 'bookmark this link' or equivalent in the popup menu