Revealing the Temperature Profile of Ultra-Hot Jupiter’s Dayside Atmosphere Using Ground-Based Telescopes

Some strongly irradiated planets exhibit thermal inversion in their dayside atmospheres (Changeat & Edwards et al. 2022). These temperature profiles are thought to result from stellar light absorbers in their atmospheres. The primary candidates for the stellar light absorption are TiO and VO, both of which are rich in absorption lines in the optical wavelengths. However, the true absorbers in the atmosphere remain unknown. KELT-9 b holds the record as the hottest planet discovered to date (Gaudi et al. 2017), with a dayside temperature reaching 4600 K (Wong et al. 2021). HST/WFC3 observations in the infrared band have confirmed the presence of thermal inversion in the atmosphere of this planet (Changeat & Edwards 2021). Contrarily, ground-based high-resolution spectroscopy in the optical band has found the absence of TiO (Kasper et al. 2021). Notably, in this extreme high-temperature environment, molecules are difficult to survive, even refractory elements. It’s crucial to note that these two observations were conducted at different wavelengths. This disparity might enable us to investigate diverse layers of the planetary atmosphere, owing to variations in optical depth. This could potentially resolve the contradiction observed in the two preceding observations. Our observational approach involves ground-based visual band observations, aiming to identify and understand temperature inversion. We employed the 1.5 m telescope equipped with a multi-band imager known as MuSCAT2, and the 1 m telescope with a single-band imager named Sinistro for our research. Using these instruments, we observed the secondary eclipses, leading to the successful detections in the i, z, and Y-bands. In our poster presentation, we provide detailed insights into our observations and engage in a discussion on KELT-9 b’s dayside temperature profile.