Comparison of Low vs. Medium Resolution Spectroscopy for Estimating Exoplanet Properties with the Gemini Planet Imager Upgrade

The Gemini Planet Imager is a coronagraphic adaptive optics instrument designed for spectroscopy of young, Jupiter-mass extrasolar planets. The Gemini Planet Imager Exoplanet Survey (GPIES), led by Principal Investigator Bruce Macintosh, observed its 531st and final new star in January 2019. Before undergoing relocation from Gemini South to Gemini North, the instrument will undergo a series of upgrades aimed at improving its detection capabilities. The principal upgrade of interest for this project is that of the spectrograph. GPI’s spectrograph currently operates with the filter bands Y, J, H, and K, with K split into two filters, with resolutions ranging from R~40 to 80. Inspired by the Subaru CHARIS spectrograph, the upgraded instrument, entitled “GPI 2.0”, will incorporate a broadband mode, simultaneously covering Y, J, H, and K, whose lower resolutions (R~9 to 15) will enable a higher signal-to-noise ratio on dim stars. With simulations from the SONORA 2018 models of cloudless planets, by Marley et. al., for the 250K-2000K range and authentic brown dwarf and star data from the IRTF SpeX Library for objects within 2000K-7000K, we modeled the performance of the current and proposed spectrographs to explore the effects of spectrographic properties on the precision of planetary temperature estimation. From the results presented by our simulations, we have hitherto deduced that measuring spectra in the H-band wavelength range at medium SNR is adequate for temperature estimation, and the inclusion of additional bands does not significantly contribute to the estimation accuracy. While the low resolution, broadband mode has exhibited up to 20% less accuracy than its companion medium resolution mode, it has demonstrated 80% accuracy in distinguishing background stars from planets. The ability to quickly make this distinction before taking higher resolution spectra will be a valuable, time-saving upgrade for future observers to leverage.