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

Abstract

We report Gemini Planet Imager H-band high-contrast imaging/integral field spectroscopy and polarimetry of theHD 100546, a 10 Myr old early-type star recently confirmed to host a thermal infrared(IR)bright(super-)Jovian protoplanet at wide separation, HD 100546 b. We resolve the inner disk cavity in polarized light, recover the thermal IR-bright arm, and identify one additional spiral arm. We easily recover HD 100546 b and show that much of its emission plausibly originates from an unresolved point source. The point-source component of HD 100546 b has extremely red IR colors compared to field brown dwarfs, qualitatively similar to young cloudy super-Jovian 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 atrproj∼14 AU, located just interior to or at the inner disk wall consistent with being a<10–20MJcandidate second protoplanet—“HD 100546c”—and lying within a weakly polarized region of the disk but along an extension of the thermal IR-bright spira larm. 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.