Near-infrared Multi-band Photometry of the Substellar Companion GJ 758 B

GJ 758 B is a cold (~600 K) companion to a Sun-like star at 29 AU projected separation, which was recently detected with high-contrast imaging. Here, we present photometry of the companion in seven photometric bands from Subaru/HiCIAO, Gemini/NIRI, and Keck/NIRC2, providing a rich sampling of the spectral energy distribution in the 1-5 μm wavelength range. A clear detection at 1.58 μm combined with an upper limit at 1.69 μm shows methane absorption in the atmosphere of the companion. The mass of the companion remains uncertain, but an updated age estimate indicates that the most likely mass range is ~30-40 M_(jup). In addition, we present an updated astrometric analysis that imposes tighter constraints on GJ 758 B's orbit and identifies the proposed second candidate companion, "GJ 758 C," as a background star.