RECOVERY OF THE CANDIDATE PROTOPLANET HD 100546 b WITH GEMINI/NICI AND DETECTION OF ADDITIONAL (PLANET-INDUCED?) DISK STRUCTURE AT SMALL SEPARATIONS

Abstract

We report the first independent, second-epoch (re-)detection of a\ndirectly-imaged protoplanet candidate. Using $L^\\prime$ high-contrast imaging\nof HD 100546 taken with the Near-Infrared Coronagraph and Imager (NICI) on\nGemini South, we recover `HD 100546 b' with a position and brightness\nconsistent with the original VLT/NaCo detection from Quanz et al, although data\nobtained after 2013 will be required to decisively demonstrate common proper\nmotion. HD 100546 b may be spatially resolved, up to $\\approx$ 12-13 AU in\ndiameter, and is embedded in a finger of thermal IR bright, polarized emission\nextending inwards to at least 0.3". Standard hot-start models imply a mass of\n$\\approx$ 15 $M_{J}$. But if HD 100546 b is newly formed or made visible by a\ncircumplanetary disk, both of which are plausible, its mass is significantly\nlower (e.g. 1--7 $M_{J}$). Additionally, we discover a thermal IR-bright disk\nfeature, possibly a spiral density wave, at roughly the same angular separation\nas HD 100546 b but 90 degrees away. Our interpretation of this feature as a\nspiral arm is not decisive, but modeling analyses using spiral density wave\ntheory implies a wave launching point exterior to $\\approx$ 0.45" embedded\nwithin the visible disk structure: plausibly evidence for a second, hitherto\nunseen wide-separation planet. With one confirmed protoplanet candidate and\nevidence for 1--2 others, HD 100546 is an important evolutionary precursor to\nintermediate-mass stars with multiple super-jovian planets at moderate/wide\nseparations like HR 8799.\n