Abstract
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-STARRS1 data and, despite its relative proximity to the
Sun (22.2$_-4.0^+6.4$ pc; Pan-STARRS1 parallax) and brightness ($J$=15.3),
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
H$\alpha$ emission and shows evidence for UV flares. The binary's weak ıt
GALEX UV emission and strong Na I 8200\AA Na absorption leads us to an age
range of $\sim$1-10Gyr. Applying this age range to evolutionary models implies
the wide companion has a mass of 0.063$\pm$0.009\,$M_ødot$. 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.
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