The scaled eclipse interval in V578 Mon increased by 192 minutes from TESS Sector 6 to Sector 87

V578 Mon has known apsidal motion. We tested its later eclipse spacing with public TESS data from three visits. We measured 19 sequences in which two eclipses of one class enclose the other eclipse. Their relative spacing gives a scaled interval. The mean intervals are 1.142266, 1.186483, and 1.275824 days in Sectors 6, 33, and 87. Sector 87 extends the earlier TESS measurements to January 2025. The first-to-last increase is 192.324 minutes. Across 18 timing and flux settings, this increase ranges from 191.496 to 193.123 minutes. A fixed-orbit test on the actual timestamps gives only 0.018 minute of apparent change. A fit with eccentricity 0.07755 and inclination 72.09 degrees gives 0.070590 degrees per cycle. Its apsidal period is 33.63 years. The Sector 87 interval is 0.496 minute below a calculation from the earlier published rate. That calculation fits orientation to the two early visits. Timing settings and synthetic flux biases exceed the sampling error of the fitted rate. Thus, we do not claim an improved physical rate or a planet. The release provides original FITS files, data hashes, all timing trials, source code, numerical checks, and figures.

V578 Mon · HD 259135 · TIC 234840976 · TESS · apsidal motion · eclipse timing · massive binary · public data · reproducible research