TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability

TL;DR

This study uses extended TESS observations and new infrared data to refine the orbital decay rate of WASP-12b, improve parameter measurements, and assess atmospheric variability, finding no significant atmospheric changes over time.

Contribution

The paper provides the first extended TESS dataset for WASP-12, significantly improving orbital and atmospheric parameter measurements and constraining atmospheric variability.

Findings

Orbital decay rate of -29.81 ms/yr confirmed with higher precision.

No significant atmospheric variability detected over multiple timescales.

Secondary eclipse depth measured at 466 ppm with consistent infrared observations.

Abstract

After observing WASP-12 in the second year of the primary mission, the Transiting Exoplanet Survey Satellite (TESS) revisited the system in late 2021 during its extended mission. In this paper, we incorporate the new TESS photometry into a reanalysis of the transits, secondary eclipses, and phase curve. We also present a new $K_s$-band occultation observation of WASP-12b obtained with the Palomar/Wide-field Infrared Camera instrument. The latest TESS photometry spans three consecutive months, quadrupling the total length of the TESS WASP-12 light curve and extending the overall time baseline by almost two years. Based on the full set of available transit and occultation timings, we find that the orbital period is shrinking at a rate of $-29.81 \pm 0.94$ ms yr$^{-1}$. The additional data also increase the measurement precision of the transit depth, orbital parameters, and phase-curve amplitudes. We obtain a secondary eclipse depth of $466 \pm 35$ ppm, a $2\sigma$ upper limit on the nightside brightness of 70 ppm, and a marginal $6\overset{\circ}{.}2 \pm 2\overset{\circ}{.}8$ eastward offset between the dayside hotspot and the substellar point. The voluminous TESS dataset allows us to assess the level of atmospheric variability on timescales of days, months, and years. We do not detect any statistically significant modulations in the secondary eclipse depth or day-night brightness contrast. Likewise, our measured $K_s$-band occultation depth of $2810 \pm 390$ ppm is consistent with most $\sim$2.2 $\mu$m observations in the literature.