Transit Photometry and Ephemeris Refinement of WASP-12 b Using TESS Data

TL;DR

This work uses TESS Sector 20 transit photometry to refine the orbital ephemeris and transit geometry of the ultra-hot Jupiter WASP-12 b. By modeling the phase-folded light curve with a physical transit model (batman/Mandel–Agol) and measuring individual mid-transit times, the authors obtain a refined ephemeris $T_c(E)=T_0+EP$ with $P$ and $T_0$ specified, and derive geometry parameters such as $R_p/R_ star$, $a/R_ star$, $i$, and $T_{14}$. The analysis yields no statistically significant transit timing variations, as indicated by a reduced $\chi^2_{\rm red}$ around unity in the O–C diagram, and confirms WASP-12 b’s highly inflated radius and near-grazing geometry. These results demonstrate the utility of TESS data for precise transit characterization and timing, providing improved predictions for future observations and enabling atmospheric and dynamical studies of this extreme system. The approach combines reproducible cloud-based data handling, robust phase-folded modeling, and timing analysis, illustrating a solid workflow for refining ephemerides of well-known exoplanets.

Abstract

We present a detailed transit photometric analysis of the ultra-hot Jupiter WASP-12 b using data from the Transiting Exoplanet Survey Satellite (TESS). The study is based on publicly available calibrated light curves and target pixel files accessed through the Mikulski Archive for Space Telescopes (MAST) cloud infrastructure. After extracting and normalizing the photometric time series, the light curve was phase-folded using an initial ephemeris and modeled with a physical transit model to determine the system's geometric parameters. From the transit modeling, we measure the planet-to-star radius ratio, orbital inclination, impact parameter, and transit duration. Adopting stellar parameters from the literature, we derive the planetary radius and transit depth, confirming the highly inflated nature of WASP-12 b. Individual mid-transit times were measured and used to refine the orbital ephemeris through a weighted linear fit. The resulting refined orbital period and reference epoch improve the predictive accuracy of future transit times over the TESS observational baseline. An observed-minus-calculated (O-C) analysis reveals no statistically significant transit timing variations, indicating that the timing data are consistent with a linear ephemeris within the measurement uncertainties. This work demonstrates the capability of TESS photometry to provide precise transit characterization and ephemeris refinement for well-studied exoplanet systems, and provides updated parameters that are relevant for future atmospheric and dynamical investigations of WASP-12 b.

Figures (7)

• Figure 1: Normalized TESS PDC_SAP light curve of WASP-12. The repeated transit events of WASP-12 b are visible across the full observational baseline.
• Figure 2: Phase-folded and binned TESS light curve of WASP-12 b using a literature ephemeris. The binning enhances the visibility of the transit signal prior to physical modeling.
• Figure 3: Phase-folded TESS light curve of WASP-12 b with the best-fitting physical transit model.
• Figure 4: Phase-folded TESS light curve of WASP-12 b with the best-fitting physical transit model (top panel) and residuals (bottom panel).
• Figure 5: Observed minus calculated (O--C) diagram for WASP-12 b based on TESS transit timing measurements. The dashed line indicates zero timing offset relative to the refined ephemeris.