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 212 268 transit times and 30 occultation times of WASP-12b spanning 2008 to 2022 2023 and find that the orbital period is decreasing at 30 29.0 ± 2 1.1 ms per year. The decay implies a stellar tidal quality factor of about 1.8 × 10^5.

1. Data

We collected 212 268 transit mid-times of WASP-12b from the literature and from literature, TESS sectors 20, 43, 44 44, 45 and 45. 71, and our own photometry from 2023, and 30 occultation times. All times are converted to BJD in the TDB standard.

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.

3. Results

Orbital decay is preferred over precession. The changing-period model is preferred, with a period derivative of -30 is -29.0 ± 2 1.1 ms per year.

3. 4. Tidal quality factor

For the stellar mass and radius of WASP-12, the period derivative implies a modified tidal quality factor of about 1.8 1.7 × 10^5. This is at the low end of values expected for a main-sequence host, which suggests the star may have begun to evolve off the main sequence. ¶ 4. Conclusion ¶ The orbit of WASP-12b is decaying, and the decay is fast enough to be measured again with a few more years of transits.