TESS fits with 31 modes show a phase departure from the 91:90 relation in KOI-54 near the Kepler frequencies from 2019 to 2024

We fit two known oscillations of the eccentric binary KOI-54 in nine public TESS sectors from 2019 to 2024. The joint model has 31 modes. The planned test concerns the target semi-amplitude ratio. Its endpoint change is +19.5%, with a conditional 95% interval of -5.4% to +48.8%. This does not establish an amplitude-ratio change. An extra phase test was selected after the amplitude results were read. On the branch near the published Kepler frequencies, the phase departure from an exact 91:90 relation is +0.120 cycles, with an interval of +0.082 to +0.159 cycles. Raw TESS-SPOC flux gives +0.085 cycles, with an interval of +0.029 to +0.146 cycles. The corrected-flux sign persists with spline baselines, a wider orbit cut, and six extra weak modes. Raw flux with six extra modes and raw QLP flux permit zero. Thus, the evidence depends on the model and product. The products use the same observations and are not combined as independent evidence. The result adds later TESS measurements of a frequency relation already known from Kepler. The intervals use time-block residual draws. Cycle aliases, unknown modes, and pipeline errors remain limits. The package supplies 20 input light curves, source records, code, fit results, figures, and reproduction instructions. No new planet or new oscillation mode is claimed.

KOI-54 · TESS · tidal oscillations · stellar phases · amplitude ratio · public light curves · reproducible astronomy