This past month the GPI team had two papers accepted, now on arXiv (Rameau et al. and Follette et al.), which bring into question the nature of the two exoplanet/protoplanet candidates previously imaged around HD 100546. HD 100546 b was identified by Quanz et al. (2013) using the NACO instrument. HD 100546 c was proposed from GPI imaging by Currie et al (2015). In these young messy environments brightened disk structures could masquerade as compact protoplanets. The two new studies demonstrate how multiwavelength analysis and followup observations along with a comparison of different algorithms can inform more complete interpretations of young disk features. The papers use a range of techniques including spectral analysis, polarization differential imaging, and spectral differential imaging in H-alpha, to demonstrate that short-wavelength emission (H-band and visible) at the location of HD 100546 b and c appear to be coming from disk scattered light rather than thermal emission from an accreting compact source. These studies do not rule out the detection of the protoplanet HD 100546 b at longer wavelengths, but provide new data that further highlights the complex disk structure and builds upon previous work.
Composite image of the complex environment of HD100546 from GPI Y-band polarization mode data, H-band spectral mode data, and MagAO H-alpha data with new and previously identified features highlighted. Further details can be found in the article by Follette et al.: https://arxiv.org/abs/1704.06260
As our group at Michigan prepares for observations of young disks with JWST NIRISS and NIRCam we are necessarily thinking about the complexity of these environments. JWST will deliver extremely high quality imaging with very low background, but at reduced resolution compared to ground-based instruments like GPI, SPHERE, and VisAO. As a community we need to be careful with interpretations of “compact” structure and leverage multi-wavelength, multi-modal instruments to advance our understanding of these exciting laboratories of planet formation.
