Keck/OSIRIS Pa${\hat{I}}^2$ high-contrast imaging and updated constraints on PDS~70b

Abstract

We present a high-contrast imaging search for Pa${\hat{I}}^2$ line emission from protoplanets in the PDS~70 system with Keck/OSIRIS integral field spectroscopy. We applied the high-resolution spectral differential imaging technique to the OSIRIS $J$-band data but did not detect the Pa${\hat{I}}^2$ line at the level predicted using the parameters of \cite{Hashimoto2020}. This lack of Pa${\hat{I}}^2$ emission suggests the MUSE-based study may have overestimated the line width of H$\hat{I}\pm$. We compared our Pa${\hat{I}}^2$ detection limits with the previous H$\hat{I}\pm$ flux and H${\hat{I}}^2$ limits and estimated $A_{\mathrm{V}}$ to be $\sim 0.9$ and 2.0 for PDS~70~b and c respectively. In particular, PDS~70~b's $A_{\mathrm{V}}$ is much smaller than implied by high-contrast near-infrared studies, which suggests the infrared-continuum photosphere and the hydrogen-emitting regions exist at different heights above the forming planet.

8pages, 5 figs, accepted for publication in AJ