A First Look at CRIRES+: Performance Assessment and Exoplanet Spectroscopy

Abstract

Abstract High-resolution spectroscopy has proven to be a powerful avenue for atmospheric remote sensing of exoplanets. Recently, ESO commissioned the CRIRES+ high-resolution infrared spectrograph at the Very Large Telescope. CRIRES+ is a cross-dispersed spectrograph with high throughput and wide wavelength coverage across the near-infrared (0.95–5.3 μm), designed to be particularly suited for atmospheric characterization of exoplanets. In this work, we report early insights into the performance of CRIRES+ for exoplanet spectroscopy and conduct a detailed assessment of the data reduction procedure. Because of the novelty of the instrument, we perform two independent data reduction strategies using the official CR2RES pipeline and our new custom-built ExoRES pipeline. Using science verification observations we find that the spectral resolving power of CRIRES+ can reach R ≳ 100,000 for optimal observing conditions. Similarly, we find the signal-to-noise ratio (S/N) to be consistent with expected and empirical estimates for the observations considered. As a case study, we perform the first application of CRIRES+ to the atmospheric characterization of an exoplanet—the ultrahot Jupiter MASCARA-1 b. We detect CO and H2O in the atmosphere of MASCARA-1 b at a S/N of 12.9 and 5.3, respectively, and a temperature inversion revealed through the CO and H2O emission lines, the first for an exoplanet. We find a combined S/N of 13.8 for CO and H2O together, with a preference for lower H2O abundance compared to CO. Our findings demonstrate the scientific potential of CRIRES+ and highlight the excellent opportunity for high-resolution atmospheric spectroscopy of diverse exoplanets.