Community exoplanet imaging data challenge for Roman CGI and starshade rendezvous

Abstract

Operating in an unprecedented contrast regime (10⁻⁷ to 10⁻⁹ ), the Roman Coronagraph Instrument (CGI) will serve as a pathfinder for key technologies needed for future Earth-finding missions such as HabEx and LUVOIR. The Roman Exoplanet Imaging Data Challenge (Roman EIDC) was a community engagement effort that tasked participants with extracting exoplanets and their orbits for a 47-UMa-like target star given: (1) 15 years of simulated precursor radial velocity (RV) data and (2) six epochs of simulated imaging taken over the course of the Roman mission. Led by the Turnbull CGI Science Investigation Team, the Roman EIDC was preceded by four tutorial “hack-a-thon” events in Baltimore, Pasadena, New York City, and Tokyo. The Roman EIDC officially launched in October 2019 and ran for 8 months, offering a unique opportunity for exoplanet scientists of all experience levels to get acquainted with realistic near-future imaging data. The Roman EIDC simulated images include four epochs with CGI’s Hybrid Lyot Coronagraph (HLC) plus two epochs with a starshade (SS) assumed to arrive as part of a Starshade Rendezvous later in the mission. We focus on our in-house analysis of the outermost planet “d,” for which the SS’s higher throughput and lower noise floor present a factor of ∼4 improvement in the signal-to-noise ratio over the narrow-field HLC. We find that, although the RV detection was marginal for planet d, the precursor RV data enabled the mass and orbit to be constrained with only two epochs of SS imaging. Including the HLC images in the analysis results in improved measurements over RV + SS alone, with the greatest gains resulting from images taken at epochs near maximum elongation. Combining the two epochs of SS imaging with the RV + HLC data resulted in a factor of ∼2 better orbit and mass determinations over RV + HLC alone. In summary, the Roman CGI, combined with precursor RV data and latermission SS imaging, forms a powerful trifecta in detecting exoplanets and determining their masses, albedos, and system configurations. While the Roman CGI will break new scientific and technological ground with direct imaging of giant exoplanets within ∼5  AU of V  ˜  5 and brighter stars, a Roman Starshade Rendezvous mission would additionally enable the detection of planets out to ∼8  AU in those systems.