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We present dayside thermal emission observations of the hottest exoplanetKELT-9b using the new MAROON-X spectrograph. We detect atomic lines in emissionwith a signal-to-noise ratio of 10 using cross-correlation with binary masks.The detection of emission lines confirms the presence of a thermal inversion inKELT-9b's atmosphere. We also use M-dwarf stellar masks to search for TiO,which has recently been invoked to explain the unusual \textit{HST}/WFC3spectrum of the planet. We find that the KELT-9b atmosphere is inconsistentwith the M-dwarf masks. Furthermore, we use an atmospheric retrieval approachto place an upper limit on the TiO volume mixing ratio of 10$^{-8.5}$ (at 99\%confidence). This upper limit is inconsistent with the models used to match theWFC3 data, which require at least an order of magnitude more TiO, thussuggesting the need for an alternate explanation of the space-based data. Ourretrieval results also strongly prefer an inverted temperature profile andatomic/ion abundances largely consistent with the expectations for a solarcomposition gas in thermochemcial equilibrium. The exception is the retrievedabundance of Fe$^+$, which is about 1-2 orders of magnitude greater thanpredictions. These results highlight the growing power of high-resolutionspectrographs on large ground-based telescopes to characterize exoplanetatmospheres when used in combination with new retrieval techniques.

Confirmation of Iron Emission Lines and Non-detection of TiO on the Dayside of KELT-9b with MAROON-X