Properties of the Nearby Brown Dwarf WISEP J180026.60+013453.1

Abstract: We present new spectroscopy and astrometry to characterize the nearby brown dwarf WISEP J180026.60+013453.1. The optical spectral type, L7.5, is in agreement with the previously reported near-infrared spectral type. The preliminary trigonometric parallax places it at a distance of $8.01 \pm 0.21$ pc, confirming that it is the fourth closest known late-L (L7-L9) dwarf. The measured luminosity, our detection of lithium, and the lack of low surface gravity indicators indicates that WISEP J180026.60+013453.1 has a mass $0.03 < M < 0.06 M_\odot$ and an age between 300 million and 1.5 billion years according to theoretical substellar evolution models. The low space motion is consistent with this young age. We have measured the rotational broadening ($v \sin i = 13.5 \pm 0.5$ km/s), and use it to estimate a maximum rotation period of 9.3 hr.