Keck observations confirm a super-Jupiter planet orbiting M dwarf OGLE-2005-BLG-071L

We present adaptive optics imaging from the NIRC2 instrument on the Keck II telescope that resolves the exoplanet host (and lens) star as it separates from the brighter source star. These observations yield the K-band brightness of the lens and planetary host star, as well as the lens-source relative proper motion, μ_rel,H, in the heliocentric reference frame. The μ_rel,H measurement allows for the determination of the microlensing parallax vector, π_E, which had only a single component determined by the microlensing light curve. The combined measurements of μ_rel,H and K_L provide the masses of the host star, M_host = 0.426 ± 0.037M_☉, and planet, m_p = 3.27 ± 0.32M_Jupiter with a projected separation of 3.4 ± 0.5 au. This confirms the tentative conclusion of a previous paper that this super-Jupiter mass planet, OGLE-2005-BLG-071Lb, orbits an M dwarf. Such planets are predicted to be rare by the core accretion theory and have been difficult to find with other methods, but there are two such planets with firm mass measurements from microlensing, and an additional 11 planetary microlens events with host mass estimates <0.5M_☉ and planet mass estimates >2 Jupiter masses that could be confirmed by high angular follow-up observations. We also point out that OGLE-2005-BLG-071L has separated far enough from its host star that it should be possible to measure the host-star metallicity with spectra from a high angular resolution telescope such as Keck, the Very Large Telescope, the Hubble Space Telescope, or the James Webb Space Telescope.