A constant period fits GD 356 phases in 13 TESS sectors from 2019 to 2024

Does the known brightness cycle of the magnetic white dwarf GD 356 keep one phase clock through 2024? We analyze all 13 mission SPOC 120-second light curves returned by a defined public archive query. We retain 189,971 measurements and fit the fundamental phase with separate sector amplitudes, second harmonics, and slow baselines. A constant period of 6937.78868 +/- 0.00191 seconds fits the sector phases. The error assumes independent one-day noise blocks. The phase test gives chi-square 7.95 for 11 degrees of freedom. Tests with aperture flux and 0.5- to 2-day baseline or noise blocks change the period by less than 0.0002 seconds. A quadratic phase term is not required. A clock fitted only to the nine sectors from 2019 to 2022 also predicts the four 2024 phases within their estimated errors. This last test is retrospective. Prior work already reported phase stability over several years. This publication adds a public timing table, a fitted clock through September 2024, and reproducible model checks. The result applies to the observed brightness fundamental under the stated model. It does not detect a planet, exclude all companions, or establish phase stability in the gaps. The package preserves the original data, archive query, hashes, code, figures, and instructions.

GD 356 · TESS · magnetic white dwarf · phase timing · ephemeris · public astronomical data