High-resolution Emission Spectroscopy of the Ultrahot Jupiter KELT-9b: Little Variation in Day- and Nightside Emission Line Contrasts

The transmission spectrum of the ultrahot Jupiter KELT-9b (T (eq) similar to 4000 K) exhibits absorption by several metal species. We searched for atomic and molecular lines in its emission spectrum by observing partial phase curves with the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs (R similar to 80,000-95,000). We find evidence for emission by Si i in the atmosphere of KELT-9b for the first time. Additionally we find evidence for emission by Mg i and Ca ii, which were previously detected in transmission, and confirmed earlier detections of Fe i emission. Conversely, we find no evidence for dayside emission from Al i, Ca i, Cr i, FeH, Fe ii, K i, Li i, Mg ii, Na i, OH, Ti i, TiO, V i, V ii, VO, and Y i. By employing likelihood mapping, we find indications of there being little variation in emission line contrast between the day- and nightsides-suggesting that KELT-9b may harbor iron emission on its nightside. Our results demonstrate that high-resolution ground-based emission spectroscopy can provide valuable insights into exoplanet atmospheres.