Program: GN-2010A-Q-23

In May and August 2009, we and collaborators used Adaptive Optics H-band direct-imaging to discover a 28 AU (projected separation) planet or brown-dwarf companion to the solar-type star GJ 758. The measured photometry and astrometry indicated a 10-40 Jupiter mass bound companion with a temperature of 550-640K. The discovery (submitted in Sep 2009 to Science Express) marks the coldest companion of a star ever imaged in thermal light. The companion is also a candidate for the coldest object ever thermally imaged outside our solar system. We propose to use Gemini NIRI to conduct multi-band photometry and astrometry of this remarkable object. The astrometry, combined with the previous data, will allow us to observe significant orbital motion, thus constraining semi-major axis, eccentricity, and object mass. Photometry (in J, H, K-cont, CH4-short, and CH4-long filters) will provide better constraints on object temperature and mass, while also giving us a first-ever glimpse into the atmosphere of the coldest imaged companion of a sun-like star.