TESS 2-min search of 307 Gaia white dwarfs (G < 18, Part 1) finds no new transit candidates, recovers WD 1856+534 b, and finds a 1.790 h red-amplitude period in WDJ000747.61+195124.94

We searched the TESS 2-min light curves of 307 white dwarfs (WDs) for transits of planets. These WDs are the first 307 of a fixed random order of the 18,438 Gaia WDs with G < 18 and TESS 2-min data (sectors 1 to 107). The search uses a box model and the fast folding algorithm, with the transit duration of each WD. Automatic flags remove harmonics, systematics and sinusoidal signals. The detection thresholds come from the noise peaks of the sample (SDE 11.0, and 16.5 for crowded apertures). An injection test with 2,456 signals measured the completeness. - The search found WD 1856+534 b (P = 1.4080 d, SDE 220.6). It found no new transit candidates. - 72 peaks above the threshold have flags. They are in 23 WDs: WD 1856+534 (harmonics), 10 WDs with periodic signals, 9 WDs with systematics near 13.7 d and 3 WDs with single-sector peaks near the threshold. - For orbital periods of 1 to 3 h, the 95% upper limit on the planet occurrence is 8.7% for 6 to 12 Earth radii and 4.9% for 12 to 22 Earth radii. - New period: WDJ000747.61+195124.94 (TIC 301788905) is a DA WD at 87 pc with a known infrared excess. TESS and ZTF together give P = 0.07457485 ± 0.00000012 d (1.78980 h). The semi-amplitude increases to the red: 0.18% in ZTF g, 0.46% in ZTF r, 1.01% in ZTF i and 1.31% in TESS. A spot on the WD does not agree with this (chi-square 139.5 for 3 degrees of freedom). The variable light agrees with a blackbody of 3040 K (1-sigma range 2690 to 3410 K). The infrared excess agrees with a blackbody of 2713 K and 0.081 solar radii (about spectral type M8 to L1). The most probable cause is the irradiated day side of a cool companion in a 1.79 h orbit. Spectroscopy and radial velocities are necessary to confirm this. The publication gives the source code, the data sources, all result tables, the vetting figures and the steps to reproduce the work. Later parts will add more WDs of the same order.

white dwarfs · TESS · transit search · planet occurrence · upper limits · injection and recovery · fast folding algorithm · box least squares · WD 1856+534 b · WDJ000747.61+195124.94 · TIC 301788905 · ZTF · post-common-envelope binary · irradiated companion · infrared excess · spectral energy distribution · white dwarf rotation · Gaia EDR3