Four fits to 2019–2024 TESS data bound a persistent 450-day sine in XO-6 b below 2.9 minutes with 120-second Gaussian sector errors

We measure 52 transit times of XO-6 b in nine public 120-second TESS light curves from 2019 to 2024. Sectors 73 and 79 add 12 transits to the seven sectors used in a previous study. The times span 4.55 years and have a 35.02-second RMS residual from a linear ephemeris. For a persistent 450-day sine with free phase, the primary conservative 95-percent amplitude upper bound is 26.53 seconds. It is 150.55 seconds when the covariance includes an added Gaussian offset with a standard deviation of 120 seconds in each sector. Four choices of flux, local trend, and limb coefficients give bounds below 170.03 seconds in that sector error test. The later 12 times alone give weak free-phase limits; the long time span is needed. A linear ephemeris fitted to the earlier 40 times predicts the later times with chi-square 11.45 for 12 degrees of freedom. We also test the published eccentric light-time shape. Its primary bound is 126.43 seconds with the 120-second sector error. These results extend earlier null tests. They do not show another planet. The limits assume a fixed Gaussian timing covariance and the stated persistent signal shapes. The package includes original FITS files, source URLs and hashes, all selection decisions, timing tables, code, simulations, and figures.

XO-6 b · TESS · transit timing · exoplanets · light-time effect · public data · correlated errors