* Astronomy

Title: A Search for High Proper Motion T Dwarfs with Pan-STARRS1 + 2MASS + WISE
Authors: Michael C. Liu, Niall R. Deacon, Eugene A. Magnier, Kimberly M. Aller, Brendan P. Bowler (IfA/Hawaii), Trent J. Dupuy (CfA/SAO), Bertrand Goldman (MPIA), W. S. Burgett, K. C. Chambers, K. W. Hodapp, N. Kaiser, R.-P. Kudritzki, J. S. Morgan (IfA/Hawaii), P. A. Price (Princeton), J. L. Tonry, R. J. Wainscoat (IfA/Hawaii)

We have searched ~8200 sq. degs for high proper motion (0.5-2.7 arcsec/year) T dwarfs by combining the first-epoch of the Pan-STARRS1 3-Pi Survey, the 2MASS All-Sky Point Source Catalogue, and the WISE Preliminary Data Release. We identified two high proper motion objects with the very red (W1-W2) colours characteristic of T dwarfs, one being the known T7.5 dwarf GJ 570D. Near-IR spectroscopy of the other object (PSO J043.5+02 = WISEP J0254+0223) reveals a spectral type of T8, leading to a photometric distance of 8.6±1.5 pc. The 2.56 arcsec/yr proper motion of PSO J043+02 is the second highest among field T dwarfs, corresponding to an exceptional tangential velocity of 104±18 km/s. According to the Besancon galaxy model, this velocity indicates membership either in the thin or thick disk, but not in the halo. Such membership is in accord with the near-IR spectrum, which points to a surface gravity (age) and metallicity typical of the field population. The proximity and brightness of PSO J043.5+02 will facilitate characterization of its atmosphere, variability, multiplicity, distance, and kinematics. The modest number of candidates from our search suggests that the immediate (~10 pc) solar neighbourhood does not contain a large reservoir of undiscovered T dwarfs earlier than about T8.

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