The First H-band Spectrum of the Giant Planet β Pictoris b

Abstract

Using the recently installed Gemini Planet Imager (GPI), we have obtained the first H-band spectrum of the planetary companion to the nearby young starβPictoris. GPI is designed to image and provide low-resolution spectra of Jupiter-sized, self-luminous planetary companions around young nearby stars. These observations were taken covering the Hband (1.65μm). The spectrum has a resolving power of∼45 and demonstrates the distinctive triangular shape of a cool substellar object with low surface gravity. Using atmospheric models, we find an effective temperature of 1600–1700 K and a surface gravity of log(g)=3.5–4.5 (cgs units). These values agree well with“hot-start” predictions from planetary evolution models for a gas giant with mass between 10 and 12MJupand age between 10 and 20 Myr.