Resolving the HD 100546 Protoplanetary System with the Gemini Planet Imager: Evidence for Multiple Forming, Accreting Planets

TL;DR

This study uses high-contrast imaging to resolve multiple potential forming planets and disk features in the HD 100546 system, providing evidence for ongoing planet formation and complex disk-planet interactions.

Contribution

First direct imaging detection of multiple protoplanet candidates and detailed disk structures in HD 100546, suggesting active planet formation.

Findings

Resolved inner disk cavity and spiral arms in polarized light.

Detected a likely second protoplanet candidate at ~14 AU.

Observed that HD 100546 b has red IR colors indicative of accretion or clouds.

Abstract

We report Gemini Planet Imager H band high-contrast imaging/integral field spectroscopy and polarimetry of the HD 100546, a 10 $Myr$-old early-type star recently confirmed to host a thermal infrared bright (super)jovian protoplanet at wide separation, HD 100546 b. We resolve the inner disk cavity in polarized light, recover the thermal-infrared (IR) bright arm, and identify one additional spiral arm. We easily recover HD 100546 b and show that much of its emission originates an unresolved, point source. HD 100546 b likely has extremely red infrared colors compared to field brown dwarfs, qualitatively similar to young cloudy superjovian planets, however, these colors may instead indicate that HD 100546 b is still accreting material from a circumplanetary disk. Additionally, we identify a second point source-like peak at $r_{proj}$ $\sim$ 14 AU, located just interior to or at inner disk wall consistent with being a 10--20 $M_{J}$ candidate second protoplanet-- "HD 100546 c" -- and lying within a weakly polarized region of the disk but along an extension of the thermal IR bright spiral arm. Alternatively, it is equally plausible that this feature is a weakly polarized but locally bright region of the inner disk wall. Astrometric monitoring of this feature over the next 2 years and emission line measurements could confirm its status as a protoplanet, rotating disk hot spot that is possibly a signpost of a protoplanet, or a stationary emission source from within the disk.