MMT/AO 5 μm Imaging Constraints on the Existence of Giant Planets Orbiting Fomalhaut at ~13-40 AU

A candidate3MJup extrasolar planet was recently imaged by Kalas et al. usingHubble Space Telescope/Advanced Camera for Surveys and Keck II at 12. �� 7 (96 AU) separation from the nearby (d = 7.7 pc) young (∼200 Myr) A2V star Fomalhaut. Here, we report results from M-band (4.8 μm) imaging of Fomalhaut on 2006 December 5 using the Clio IR imager on the 6.5 m MMT with the adaptive secondary mirror. Our images are sensitive to giant planets at orbital radii comparable to the outer solar system (∼10–40 AU). Comparing our 5σ M-band photometric limits to theoretical evolutionary tracks for substellar objects, our results rule out the existence of planets with masses >2 MJup from ∼13 to 40 AU and objects >13 MJup from ∼ 8t o 40 AU.