Detection of TiO and VO in the Atmosphere of WASP-121b and Evidence For its Temporal Variation

• Published in: Research in astronomy and astrophysics Vol. 23; no. 6; pp. 65010 - 115
• Main Authors: Ouyang, Qinglin, Wang, Wei, Zhai, Meng, Chen, Guo, Rojo, Patricio, Liu, Yujuan, Zhao, Fei, Huang, Jia-Sheng, Zhao, Gang
• Format: Journal Article
• Language: English
• Published: Beijing National Astromonical Observatories, CAS and IOP Publishing 01.06.2023; IOP Publishing; School of Astronomy and Space Science,University of Chinese Academy of Sciences(UCAS),Beijing 100049,China%CAS Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China%Chinese Academy of Sciences South America Center for Astronomy(CASSACA),National Astronomical Observatories,Beijing 100101,China%CAS Key Laboratory of Planetary Sciences,Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210023,China%Departamento de Astronomía,Universidad de Chile,Camino El Observatorio 1515,Las Condes,Santiago,Chile%School of Astronomy and Space Science,University of Chinese Academy of Sciences(UCAS),Beijing 100049,China; Chinese Academy of Sciences South America Center for Astronomy(CASSACA),National Astronomical Observatories,Beijing 100101,China; CAS Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100101,China
• Subjects: Abundance; Astrophysical research; Chemical composition; Extrasolar planets; Gas giant planets; Gaussian process; Jupiter; Light curve; methods: data analysis; Planetary Systems; planets and satellites: atmospheres; Rayleigh scattering; Reference stars; Retrieval; Spectra; Spectrophotometry; Spectroscopy; stars: individual (WASP-121); techniques: spectroscopic; Transit; techniques:spectroscopic; planets and satellites:atmospheres; Planetary Systems; methods:data analysis; stars:individual(WASP-121)
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/accbb2

We report the transit observations of the ultra-hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph at the 4 m ground-based Southern Astrophysical Research Telescope, covering the wavelength range 502–900 nm. By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry, we derive spectroscopic transit light curves and fit them using a Gaussian process framework to determine transit depths for every passband. The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength, which seems to be too steep to be accounted for by Rayleigh scattering alone. We note that the transmission spectrum from this work and other works differ obviously from each other, which was pointed out previously by Wilson et al. as evidence for temporal atmospheric variation. We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum. We determine TiO, VO and H 2 O with abundances of − 5.95 − 0.42 + 0.47 dex, − 6.72 − 1.79 + 0.51 dex and − 4.13 − 0.46 + 0.63 dex, respectively. We compare the abundances of all three of these molecules derived from this work and previous works, and find that they are not consistent with each other, indicating the chemical compositions of the terminator region may change over long timescales. Future multi-epoch and high-precision transit observations are required to further confirm this phenomenon. We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis, the abundances of V and VO, the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.