Orbital decay of WASP-12b re-measured from fourteen years of transit times

Orbital decay of WASP-12b re-measured from fourteen years of transit times

We fit 212 318 transit times and 41 occultation times of WASP-12b spanning 2008 to 2022 2025 and find that the orbital period is decreasing at 30 29.1 ± 2 0.9 ms per year. Apsidal precession is disfavoured by a Bayes factor above 1000. The decay implies a modified stellar tidal quality factor of about 1.8 (1.7 ± 0.1) × 10^5.

1. Data

We collect 212 collected 318 transit mid-times of WASP-12b from the literature and from literature, TESS sectors 20, 43, 44 44, 45, 71 and 45. 72, and our own photometry from 2023 to 2025, and 41 occultation times. All times are converted to BJD in the TDB standard. standard, and each literature time is refit from its light curve where the light curve is public.

2. Timing model

We fit compare three models by nested sampling: a constant-period model and a model with constant period, a steadily changing period. period, and apsidal precession of a slightly eccentric orbit. Occultation times break the degeneracy between decay and precession, because precession shifts transits and occultations in opposite directions. Timing uncertainties are inflated by a jitter term fit jointly with the model.

3. Results

Orbital decay is preferred over precession by a Bayes factor above 1000. The changing-period model is preferred, with a period derivative of -30 is -29.1 ± 2 0.9 ms per year. year, and the residuals show no periodic signal above 30 seconds.

3. 4. Tidal quality factor

For the stellar mass and radius of WASP-12, WASP-12 from asteroseismic scaling, the period derivative implies a modified stellar tidal quality factor of about 1.8 (1.7 ± 0.1) × 10^5. This favours a host that has begun to evolve off the main sequence, where tidal dissipation in the radiative core is at the low end of values expected for a main-sequence host, which suggests the star may be a subgiant. efficient.

4. Conclusion References

Yee, S. W. et al. (2020). The orbit of WASP-12b is decaying, and the decay is fast enough to be measured again with a few more years of transits. decaying. ApJL 888, L5.