2014ApJ...786...32M

We present the first ground-based CCD (λ < 1 µm) image of an extrasolar planet. Using the Magellan Adaptive Optics system's VisAO camera, we detected the extrasolar giant planet β Pictoris b in Y-short (Y_S, 0.985 µm), at a separation of 0.470±0.''010 and a contrast of (1.63±0.49)x10^–5. This detection has a signal-to-noise ratio of 4.1 with an empirically estimated upper limit on false alarm probability of 1.0%. We also present new photometry from the Gemini Near-Infrared Coronagraphic Imager instrument on the Gemini South telescope, in CH_4S,1%(1.58 µm), K_S(2.18 µm), and K_cont(2.27 µm). A thorough analysis of our photometry combined with previous measurements yields an estimated near-IR spectral type of L2.5±1.5, consistent with previous estimates. We estimate log (L_bol/L_☉) = -3.86±0.04, which is consistent with prior estimates for β Pic b and with field early-L brown dwarfs (BDs). This yields a hot-start mass estimate of 11.9±0.7 M_Jup for an age of 21±4 Myr, with an upper limit below the deuterium burning mass. Our L_bol-based hot-start estimate for temperature is T_eff= 1643±32 K (not including model-dependent uncertainty). Due to the large corresponding model-derived radius of R = 1.43±0.02 R_Jup, this T_eff is ∼250 K cooler than would be expected for a field L2.5 BD. Other young, low-gravity (large-radius), ultracool dwarfs and directly imaged EGPs also have lower effective temperatures than are implied by their spectral types. However, such objects tend to be anomalously red in the near-IR compared to field BDs. In contrast, β Pic b has near-IR colors more typical of an early-L dwarf despite its lower inferred temperature.