Local fits to nine TESS sectors show no clear linear change in TOI-1431 b transit width from 2019 to 2024

We test for a linear change in the transit width of TOI-1431 b, also called MASCARA-5 b. We fit 76 complete transits in nine public two-minute TESS sectors from 2019 to 2024. Each event has a free center, depth, width, and local baseline. The measured width is the intrinsic full width at half depth before exposure averaging. A linear fit gives each sector equal weight. The primary corrected-flux slope is +0.048 minutes per year. Its nominal 95% Student t interval is -0.114 to +0.210 minutes per year, with seven residual degrees of freedom. This interval assumes independent, approximately normal sector errors with a common variance. All eight flux, baseline, window, and shape variants give intervals that include zero. The aperture-flux slope is -0.077 minutes per year. An added paired diagnostic gives a slope of -0.125 minutes per year for aperture minus corrected width. Its nominal 95% interval is -0.229 to -0.022 under the same sector model. This exploratory result shows that the processing choice matters for a small trend limit. The data do not isolate the cause of this difference. In a conditional recovery test with zero input slope, 92.9% of the simulated intervals contain zero. This test uses a finite cache of fitted residual shifts. It does not establish exact 95% coverage. Detector positions and pipeline versions change with time. The result is a conditional limit on this width observable. It does not establish a constant orbit or measure orbital precession. The package contains the original FITS files, data provenance, source code, fit tables, numerical checks, signal recovery trials, and figures.

TOI-1431 b · MASCARA-5 b · TESS · transit width · transit duration variation · FWHM · public astronomical data · reproducible research