Discovery of a 0.15" Binary Brown Dwarf 2MASSJ 1426316+155701 With Gemini/Hokupa'a Adaptive Optics

L. M. Close; D. Potter; W. Brandner; M. Lloyd-Hart; J. Liebert; A. Burrows; N. Siegler

doi:10.1086/337916

paper

Discovery of a 0.15" Binary Brown Dwarf 2MASSJ 1426316+155701 With Gemini/Hokupa'a Adaptive Optics

arXiv:astro-ph/0110669 · doi:10.1086/337916

Abstract

Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15" binary (2MASSJ 1426316+155701). The companion is about half as bright as the primary (Delta K = 0.61+/-0.05 $, D e l t a H = 0.70 + / - 0.05) an d ha se v e n r e dd er co l or sH - K = 0.59 + / - 0.14 t han t h e p r ima r y . T h e b l e n d e d s p ec t r u m o f t h e bina r y ha s b ee n p r e v i o u s l y d e t er min e d t o b e M 9.0. W e m o d e l e d ab l e n d o f an M 8.5 t e m pl a t e an d a L 1 - L 3 t e m pl a t er e p r o d u c in g a M 9.0 s p ec t r u min t h ec a seo f D e l t a K = 0.61 + / - 0.05, D e l t a H = 0.70 \pm 0.05$ . These spectral types also match the observed H-K colors of each star. Based the previously observed low space motion and $H_{I^} \pm$ activity we assign an age of $0. 8_{- 0.3}^{+ 6.7} G y r$ . Utilizing this age range and the latest DUSTY models of the Lyon group we assign a photometric distance of $18. 8_{- 1.02}^{+ 1.44} p c$ and masses of $M_{A} = 0.07 4_{- 0.011}^{+ 0.005} M_{⊙}$ and $M_{B} = 0.06 6_{- 0.015}^{+ 0.006} M_{⊙}$ . We therefore estimate a system separation of $2.9 2_{+ 0.22}^{- 0.16} A U$ and a period of $13.3 + 3.18^{- 1.51} y r$ respectively. Hence, 2M1426 is among the smallest separation brown dwarf binaries resolved to date.