James Webb Space Telescope Feed Post

Harvard ADS: Constraining Planetary Albedo of JWST Targets in the TESS bandpass, using TESS, HST and Spitzer Eclipse Depth Observations

Paper abstract: Albedo is one of the important characteristics of hot Jupiter exoplanets. However, albedo constraints have been obtained for very few exoplanets. In this work, we present the TESS Phase Curve observations of WASP-18b, WASP-19b, WASP-121b, WASP-43b, WASP-17b, and WASP-77b, all JWST targets for atmospheric characterization and constrain their occultation depth as well as geometric albedo (A_g). We use a grid of self-consistent model atmospheres to constrain the metallicity, C/O ratio, and heat re-distribution for these six targets by fitting to their HST and/or Spitzer observations and also compute the thermal contribution to total occultation depth in the TESS bandpass. We report the first value of TESS occultation depth for WASP-17b (151_{-66}^{+83}) and updated value for WASP-77Ab (94_{-62}^{+53}). We find self-consistent models constrain high values of thermal contribution to total occultation compared to Planck models. We find very low A_g values for WASP-18b (< 0.089), WASP-19b (< 0.022), WASP-121b (0.0^{+0.055}_{-0.104}), WASP-77Ab (0.017^{+0.126}_{-0.147}) and significantly higher value for WASP-43b (0.109^{+0.086}_{-0.088}) and WASP-17b (0.401^{+0.526}_{-0.307}). We find WASP-17b lies in the ideal spot of low gravity and low equilibrium temperature, conducive for cloud formation, leading to high A_g. With the best-fit models, we constrain low heat re-distribution for all planets, with WASP-18b having the least. We also constrain sub-solar metallicity for all planets except WASP-17b and WASP-19b. We find a highly sub-solar C/O ratio for WASP-77Ab and WASP-43b, solar for WASP-18b, and super-solar for WASP-121b. The best-fit P-T profiles show thermal inversion for WASP-18b and WASP-121b and none for WASP-77b and WASP-43b, which is in agreement with previous works.