Keck/OSIRIS Paβ High-contrast Imaging and Updated Constraints on PDS 70b

Abstract

We present a high-contrast imaging search for Pa β 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 β line at the level predicted using the parameters of Hashimoto et al. (2020). This lack of Pa β emission suggests the MUSE-based study may have overestimated the line width of H α . We compared our Pa β detection limits with the previous H α flux and H β limits and estimated A V to be ∼0.9 and 2.0 for PDS 70 b and c, respectively. In particular, PDS 70 b’s A 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.