WASP-121b Secondary Eclipses Revisited Using TESS Observation

Abstract

We present the detection and characterization of the ultrahot Jupiter WASP-121b (${{R}_{p}} \simeq 1.865{\kern 1pt} {{R}_{J}}$, ${{M}_{p}} \simeq 1.184{\kern 1pt} {{M}_{J}}$) around F6 spectral type star ($V{{ = 10.4}^{m}}$) using observations from the Transiting Exoplanet Survey Satellite (TESS). The host star is located $270.0 \pm 90.0$ pc away with a radius of $(1.45 \pm 0.03){\kern 1pt} {{R}_{ \odot }}$ and a mass of $(1.35 \pm 0.06){\kern 1pt} {{M}_{ \odot }}$. We study the publicly available data collected by the TESS in sector 7. We apply Gaussian processes (GPs) to model the systematic noise and the Markov Chain Monte Carlo (MCMC) method to fit it to the data. After removing the instrumental systematic noise, we reliably detect the secondary eclipse with a depth of $486_{{ - 25}}^{{ + 24}}$ parts-per-million (ppm) and planet-to-star radius ratio, $p = 0.1237_{{ - 0.0002}}^{{ + 0.0001}}$. The transit ephemeris of WASP-121b is updated using the MCMC method. Finally, to complement our study, we use updated ephemeris to investigate transit time variations (TTVs) for WASP-121b. We observe small variations from the constant-period models in our transit time data.