Comprehensive Analysis of the Full TESS Orbital Phase Curve of WASP121b

Abstract

We present the full phase curve analysis of the ultrahot Jupiter WASP-121b using observations from the Transiting Exoplanet Survey Satellite (TESS). Our comprehensive phase curve model includes primary transit, secondary eclipse, thermal emission, reflection, and ellipsoidal tidal distortion. After removing the instrumental systematic noise, we reliably detect the secondary eclipse with a depth of 489₋₁₀⁺¹⁶ parts-per-million (ppm), dominated by thermal emission. Using the TESS bandpass, we measure the dayside 2941₋₁₅₀⁺⁶¹K and nightside 2236₋₉₇⁺³⁸K temperatures of WASP-121b. We find that a hotspot is well aligned with the substellar point, leading to the conclusion that there is an inefficient heat distribution from the dayside to the nightside. Our estimated geometric albedo, A_g = 0.069_−0.02^+0.06, suggest that WASP-121b has a low geometric albedo.