Limits on Quaoar’s Atmosphere

The Kuiper Belt Object Quaoar, located well beyond the orbit of Pluto, can be studied through occultations as it passes along the line of sight through the crowed plane of the Milky Way. Recent "near-misses" provide some constraints, as Wesley Fraser (National Research Council Herzberg, Canada) and collaborators rule out some pure N₂ and CO models. They find that a methane atmosphere is possible, with temperature and pressure values that prevented detectability in the latest observations. The background stars are relatively faint, and rapid photometry is required, so the acquisition camera on Gemini, normally used to adjust the telescope pointing, unusually became the science instrument. Full results from observations on July 13, 2013, at Gemini South are published in The Astrophysical Journal Letters, with more details about the occultation prediction technique in Publications of the Astronomical Society of the Pacific. A Gemini web feature appears here.