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

Abstract

The transmission spectrum of the ultrahot Jupiter KELT-9b ( T eq ∼ 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 ∼ 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.