Comprehensive analysis of TESS Full Orbital Phase Curve of WASP-121b

Abstract

We present the full phase curve analysis of the ultrahot Jupiter WASP-121b ($R_p \simeq 1.865 R_J, M_p \simeq 1.184 M_J $) using observations from the Transiting Exoplanet Survey Satellite (TESS) and a comparison between our results with previous studies on this target. Our comprehensive phase curve model includes primary transit, secondary eclipse, thermal emission, reflection, and ellipsoidal tidal distortion, which are jointly fit to extract the information of all parameters simultaneously from the data sets. We also evaluated and calculated the amplitude of Doppler beaming to be $\sim 2$ ppm, but given the precision of the photometric data, we found it to be insignificant. 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 $2941_{-150}^{+61} K$ and nightside $2236_{-97}^{+38} K $ 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. Finally, our estimated amplitude of the ellipsoidal variation signal is in agreement with the predictions of the theoretical expectations.