2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary Article Swipe
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· 2017
· Open Access
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· DOI: https://doi.org/10.1093/mnras/stx065
· OA: W2583066622
We present the discovery of a 360 au separation T3 companion to the tight (3.1 au) M4.5+M6.5 binary 2MASS J02132062+3648506. This companion was identified using Pan-STARRS 1 data and despite its relative proximity to the Sun (22.2_{-4.0}^{+6.4} pc; Pan-STARRS 1 parallax) and brightness (J = 15.3), it appears to have been missed by previous studies due to its position near a diffraction spike in 2MASS. The close M dwarf binary has active X-ray and Hα emission and shows evidence for UV flares. The binary's weak GALEX UV emission and strong Na i 8200 Å Na absorption lead us to an age range of ∼1-10 Gyr. Applying this age range to evolutionary models implies that the wide companion has a mass of 0.063 ± 0.009 M⊙. 2MASS J0213+3648 C provides a relatively old benchmark close to the L/T transition and acts as a key, older comparison to the much younger early-T companions HN Peg B and GU Psc b.
