Proper Motion of the Faint Star near KIC 8462852 (Boyajian's Star)—Not a Binary System

A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m adaptive optics imaging in the JHK near-infrared (NIR) in 2014 by Boyajian et al. (2016). The closeness of the star to KIC 8462852 suggested that the two could constitute a binary, which might have implications for the cause of the brightness dips seen by Kepler and in ground-based optical studies. Here, NIR imaging in 2017 using the Mimir instrument resolved the pair and enabled measuring their separation. The faint star had moved 67 ± 7 milliarcsec (mas) relative to KIC 8462852 since 2014. The relative proper motion of the faint star is 23.9 ± 2.6 mas yr^-1, for a tangential velocity of 45 ± 5 km s^-1 if it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750 au current projected separation is 1.5 km s^-1, hence the star pair cannot be bound.