While quality checking a new motion-aware co-addition of all 12.5 months of WISE data, the source WISE J070720.48+170533.0 was found to have moved 0.9 arc-sec in 6 months. Backtracking this motion allowed us to identify this source as 2MASS J07071961+1705464 and with several entries in the USNO B catalog. An astrometric fit to these archival data gives a proper motion of 1793 +/- 2 mas/yr and a parallax of 35 +/- 42 mas. Photometry from WISE, 2MASS and the POSS can be fit reasonably well by a blackbody with T = 3658 K and an angular radius of 4.36E-11 radians. No clear evidence of H_2 collision-induced absorption is seen in the near-IR. An optical spectrum shows broad deep CaH bands at 638 and 690 nm, broad deep Na D at 598.2 nm, and weak or absent TiO, indicating that this source is an ultra-subdwarf M star with a radial velocity about -21 +/- 18 km/sec relative to the Sun. Given its apparent magnitude, the distance is about 39 +/- 9 pc and the tangential velocity is probably about 330 km/sec, but a more precise parallax is needed to be certain.
@article{arxiv.1310.6717,
title = {The First AllWISE Proper Motion Discovery: WISEA J070720.50+170532.7},
author = {Edward L. Wright and J. Davy Kirkpatrick and Christopher R. Gelino and Sergio Fajardo-Acosta and Gregory Mace and Peter R. Eisenhardt and Daniel Stern and Ian S. McLean and M. F. Skrutskie and Apurva Oza and M. J. Nelson and Michael C. Cushing and I. Neil Reid and Michele Fumagalli and Adam J. Burgasser},
journal= {arXiv preprint arXiv:1310.6717},
year = {2015}
}
Comments
Accepted by the Astronomical Journal, 10 pages LaTex with 9 embedded figures. UCAC and CMC data added, fits updated