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 directly imaged protoplanet candidate. Using L′high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager on Gemini South, were cover “HD 100546 b” with a position and brightness consistent with the original Very Large Telescope/NAos-COnica detection from Quanz et al., although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546 b may be spatially resolved, up to≈12–13 AU in diameter, and is embedded in a finger of thermal IR-bright, polarized emission extending inward to at least 0.′′3. Standard hot-start model simply a mass of≈15MJ. However, if HD 100546 b is newly formed or made visible by a circumplanetary disk,both of which are plausible, its mass is significantly lower (e.g., 1–7MJ). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughly the same angular separation as HD 100546 bbut 90◦away. Our interpretation of this feature as a spiral arm is not decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to≈0.′′45 embedded within the visible disk structure:plausibly evidence for a second, hitherto unseen, wide-separation planet. With one confirmed protoplanet candidate and evidence for one to two others, HD 100546 is an important evolutionary precursor to intermediate-mass stars with multiple super-Jovian planets at moderate/wide separations like HR 8799.