A Roman Coronagraph Spectroscopic Mode Demonstration

Abstract

We propose 730 nm high-contrast spectroscopic observations of selected self-luminous directly-imaged planets as a key test of the Roman Coronagraph's planet characterization capabilities. The planet sample draws from ground-based IR discoveries with the NASA headquarters-supported Subaru/OASIS survey -- HIP 99770 b and HIP 54515 b -- and ``emblematic" planets $\beta$ Pic b and HR 8799 e. All of these planets are likely unsuitable for achieving the coronagraph's core TTR5 goal at 575 nm but are detectable at longer wavelength passbands. Their predicted contrasts at 730 $\mu m$ cover two orders of magnitude range; all companions reside within the dark hole region enabled by the shaped-pupil coronagraph at 730 nm. These observations will help to fulfill multiple Coronagraph Objectives, providing a first assessment of the wavelength dependence of speckle noise and the ability to extract accurate atmospheric information in the face of this noise. Additionally, they will provide a first experiment at extracting optical planet spectra in the face of signal contamination from a debris disk: prefiguring challenges that the Habitable Worlds Observatory may encounter with imaging Earths in exozodi-contaminated systems.