Unifying High- and Low-resolution Observations to Constrain the Dayside Atmosphere of KELT-20b/MASCARA-2b

Abstract We present high-resolution dayside thermal emission observations of the exoplanet KELT-20b/MASCARA-2b using MAROON-X spectrograph. Applying cross-correlation method with both empirical and theoretical masks a retrieval analysis, we confirm previous detections Fe i lines detect Ni for first time in planet (at 4.7 σ confidence). do not see evidence additional species data, including notably predicted inversion agents TiO VO, their atomic constituents Ti V , previously claimed ii Cr . also perform joint existing Hubble Space Telescope/WFC3 spectroscopy Spitzer/IRAC photometry. This allows us to place bounded constraints on abundances H 2 O, CO, stringent upper limit abundance. The results are consistent KELT-20b having solar slightly supersolar composition atmosphere terms bulk metal enrichment, carbon-to-oxygen iron-to-oxygen ratios. However, volume mixing ratio (10 −7.6 at 99% confidence) is inconsistent this picture, which, along nondetection points sequestration species, possibly due nightside condensation. lack but presence large O feature WFC3 data challenging reconcile within context 1D self-consistent, radiative-convective models.