Four tested additive harmonic corrections change TOI-1518 b mean odd transit coefficients by less than 12 ppm

We test whether brightness changes measured outside eclipses can explain a reported odd transit coefficient for TOI-1518 b. We use five public 120 s TESS SPOC light curves from 2022 and 2024. We reproduce the 60-event sample and fixed spherical transit estimator from SCI d2a68e90-16ff-4bda-9c9b-c76f1176ff51. Each event has a free center time, width, depth, local quadratic background, and odd coefficient. In each sector, we fit a slow baseline and additive sine and cosine terms at exact orbital harmonics. The fit excludes samples within 0.075 day of either eclipse. We subtract only the fitted harmonic terms and fit each transit again. The tested cutoffs are 2, 4, 8, 12, and 20 harmonics. For the first four cutoffs, each mean changes by less than 12 parts per million (ppm). At 12 harmonics, the corrected means are 121.0, 50.7, and 82.1 ppm. These values refer to 2022, early 2024, and late 2024. The original means are 120.2, 61.9, and 84.5 ppm. A cutoff of 20 harmonics gives larger changes and weaker constraints across the excluded transit phases. Approximate intervals use matched orbit resampling and a local transit response. Mask and baseline controls give similar 12-harmonic point estimates. A raw-flux control keeps positive means but changes the early-2024 value by 22.6 ppm. Synthetic transit signals survive the correction. This result applies to the stated additive harmonic family. It does not exclude spatial stellar pulsations, other frequencies, or errors shared by many transits. It does not establish a physical cause or a new planet. The package preserves the original FITS files, source code, archive records, event fits, uncertainty draws, checks, and figures.

TOI-1518 b · TESS · transit asymmetry · orbital harmonics · stellar variability · eclipse mask · reproducible research