On the Age of the Widest Very Low Mass Binary

Abstract

We have recently identified the widest very low-mass binary (2M0126AB), consisting of an M6.5V and an M8V dwarf with a separation of ~5100 AU, which is twice as large as that of the second widest known system and an order of magnitude larger than those of all other previously known wide very low-mass binaries. If this binary belongs to the field population, its constituents would have masses of ~0.09 Msun, at the lower end of the stellar regime. However, in the discovery paper we pointed out that its proper motion and position in the sky are both consistent with being a member of the young (30 Myr) Tucana/Horologium association, raising the possibility that the binary is a pair of ~0.02 Msun brown dwarfs. We obtained optical spectroscopy at the Gemini South Observatory in order to constrain the age of the pair and clarify its nature. The absence of lithium absorption at 671 nm, modest Halpha emission, and the strength of the gravity-sensitive Na doublet at 818 nm all point toward an age of at least 200 Myr, ruling out the possibility that the binary is a member of Tucana/Horologium. We further estimate that the binary is younger than 2 Gyr based on its expected lifetime in the galactic disk.

accepted for publication in The Astrophysical Journal

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• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
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• Discovery of the first wide L dwarf + giant binary system and eight other ultra-cool dwarfs in wide binaries
• Discovery of a Very Low Mass Triple with Late-M and T Dwarf Components: LP 704-48/SDSS J0006-0852AB
• Discovery of the Widest Very Low Mass Field Binary
• WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9
• Shaping the Brown Dwarf Desert: Predicting the Primordial Brown Dwarf Binary Distributions from Turbulent Fragmentation
• The Brown Dwarf Kinematics Project (BDKP). II. Details on Nine Wide Common Proper Motion Very Low-Mass Companions to Nearby Stars