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

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.

• The paper refines WASP-12b's orbital decay by measuring a shortening rate of -29.81 ± 0.94 ms/yr using extended TESS transit data.
• The paper assesses atmospheric variability and finds no significant changes in secondary eclipse depths or dayside brightness contrasts.
• The paper presents consistent secondary eclipse metrics that support improved tidal dissipation models and atmospheric stability in ultra-hot Jupiters.

Updated Observations and Analysis of WASP-12: Orbital Dynamics and Atmospheric Characteristics

The paper "TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability" presents a thorough reexamination of the exoplanet WASP-12b using new observational data obtained from the Transiting Exoplanet Survey Satellite (TESS). WASP-12b, a prototype ultra-hot Jupiter, has been extensively studied since its discovery, characterized by an inflated radius, rapid orbital period, and high equilibrium temperature due to proximity to its host star. The focus of this study is to improve constraints on WASP-12b's orbital decay and assess potential variability in its atmospheric brightness over time.

Key Findings

1. Orbital Decay Refinement: The paper reports a refined measurement of WASP-12b's orbit decay rate, using both previously published transit data and new TESS observations capturing approximately two more years of data. The authors find that the orbital period is shortening at a rate of $-29.81 \pm 0.94$ ms/yr. This result solidifies and updates previous decay rate estimates.
2. Atmospheric Analysis: The research employs the extensive TESS dataset to evaluate levels of atmospheric variability from WASP-12b. Notably, the study finds no statistically significant modulations in the secondary eclipse depth or contrast between dayside and nightside brightness. The analysis of the phase curve indicates a marginal eastward shift in dayside brightness, suggesting dynamically active atmospheric circulation.
3. Secondary Eclipse Metrics: The paper presents refined measurements of the secondary eclipse depth in different spectral bands, particularly noting a TESS-band depth of $466 \pm 35$ ppm and a consistent $K_s$-band depth across observations. These consistent measurements align well with previously recorded near-infrared observations.

Practical and Theoretical Implications

• Tidal Hydrodynamics: The detected rate of orbital decay provides insights into the tidally induced dissipation occurring within the host star. The paper discusses implications for the modified tidal quality factor $Q'_*$, finding it to be significantly lower than commonly assumed for similar stars, fueling further discussion about tidal interactions and stellar evolution.
• Atmospheric Stability: The study's finding of consistent dayside emission and a lack of significant atmospheric variability offers a benchmark for modeling atmospheric dynamics of similar exoplanets. It suggests robust dynamics that may stabilize atmospheric processes against fluctuations that could arise from variability in stellar irradiation or intrinsic atmospheric processes.

Future Directions

The paper highlights several directions for future research, notably improved temporal monitoring of WASP-12b's transit and occultation timings. Extending these observations with high precision over longer baselines will help resolve the mechanics behind the rapid orbital decay. Further, advancing atmospheric models to interpret the phase-curve results in more detail could shed light on the atmospheric circulation patterns causing the observed eastward shift of the hotspot.

In conclusion, this study significantly enhances the understanding of WASP-12b's orbital and atmospheric characteristics, leveraging the comprehensive dataset from TESS to refine orbital parameters and systematically address claims of atmospheric variability. These results have substantial implications for exoplanetary science, particularly in characterizing tidal interactions and atmospheric dynamics in hot Jupiters.