TESS data show a smaller eclipse gap in V402 Lac from 2019 to 2024

We measure eclipse times in four public TESS visits to the eccentric binary V402 Lac. We use 46 eclipses to form 15 complete primary-secondary-primary triplets. The gap fraction is the time from primary to secondary eclipse divided by the time between adjacent primary eclipses. It does not change under a common constant or linear change in those three times. The SAP flux gap fraction falls from 0.636021 in 2019 to 0.620968 in 2024. The endpoint change is -0.015054 with an internal error of 0.000117. On the scale of the published 3.782043-day period, this is a decrease of 82.0 minutes. Ten fit and flux variants give decreases from 79.2 to 82.0 minutes. Spherical eclipse controls on the real timestamps change the endpoint estimator bias by less than two seconds. A Kepler model with the published eccentricity and inclination gives a conditional advance near 0.0086 degrees per cycle. This supports continued advance of periastron on the published scale. The flux reduction and adopted orbit limit the rate accuracy. We do not infer a new planet or a separate relativistic effect. The package includes the source FITS data, selection audit, code, covariance matrices, results, and offline run instructions.

V402 Lac · TIC 468792279 · TESS · eclipsing binary · apsidal motion · eclipse timing · public data · reproducible analysis