Near-infrared detection and characterization of the exoplanet HD 95086 b with the Gemini Planet Imager

HD 95086 is an intermediate-mass debris-disk-bearing star. VLT/NaCo 3.8 μm observations revealed it hosts a 5 ± 2 M_Jup companion (HD 95086 b) at ≃56 AU. Follow-up observations at 1.66 and 2.18 μm yielded a null detection, suggesting extremely red colors for the planet and the need for deeper direct-imaging data. In this Letter, we report H-(1.7 μm) and K₁-(2.05 μm) band detections of HD 95086 b from Gemini Planet Imager (GPI) commissioning observations taken by the GPI team. The planet position in both spectral channels is consistent with the NaCo measurements and we confirm it to be comoving. Our photometry yields colors of H - L' = 3.6 ± 1.0 mag and K₁ - L' = 2.4 ± 0.7 mag, consistent with previously reported 5-σ upper limits in H and Ks. The photometry of HD 95086 b best matches that of 2M 1207 b and HR 8799 cde. Comparing its spectral energy distribution with the BT-SETTL and LESIA planet atmospheric models yields T_eff ~ 600-1500 K and log g ~ 2.1-4.5. Hot-start evolutionary models yield M = 5 ± 2 M_Jup. Warm-start models reproduce the combined absolute fluxes of the object for M = 4-14 M_Jup for a wide range of plausible initial conditions (S_init = 8-13 k_B/baryon). The color-magnitude diagram location of HD 95086 b and its estimated T_eff and log g suggest that the planet is a peculiar L - T transition object with an enhanced amount of photospheric dust.

Based on public data taken at the GPI commissioning.