A cubic clock fits HW Vir's 2016–2022 space data better than a quadratic clock when constant mission offsets are at most one second

We test a quadratic eclipse clock for HW Vir with public 2016 K2 and 2021 TESS photometry and 19 CHEOPS times from 2020–2022. We fit one eclipse time and one local period per photometry segment and retain their covariance. The local period increase is 2.581 +/- 0.747 ms. A quadratic closure test gives -19.704 +/- 6.225 s. We fit quadratic and cubic clocks with extra independent Gaussian scatter in the CHEOPS times. With constant TESS and CHEOPS offsets each within +/-1 s of K2, the cubic improves twice the log likelihood by 55.21. None of 1,000 simulations from the fitted quadratic null gives this large an improvement. The statistic is 61.06 with zero offsets. It falls to 2.20 when the local periods receive negligible weight. It falls to 6.12 with a shared 2 s error within each CHEOPS year. A free-offset quadratic fit gives offsets near -7 s and remains possible. The zero-offset cubic misses two held-out 2024 ground times by 6.45 and 12.04 s. The result is conditional on the noise and mission-offset models. It does not establish a planet or a secure future clock. The package preserves raw FITS data, source tables and hashes, code, covariance matrices, simulations, controls, figures, and offline reproduction instructions.

HW Vir · eclipsing binary · eclipse timing · K2 · TESS · CHEOPS · local orbital period · time covariance · quadratic clock · cubic clock · mission offsets · reproducible astronomy