A Candidate Outburst of the Cool ZZ Ceti Star LP 119-10 in Archival TESS and ZTF Photometry

Abstract

LP 119-10 (WD 0502+540, TIC 252385237) is a known hydrogen-atmosphere pulsating white dwarf (ZZ Ceti star, DAV) near the cool edge of the instability strip. This preprint reports a single brightening event found in archival TESS 120-s photometry of sector 86. On 2024 December 4 the flux in the photometric aperture rose by 6.5 ± 0.3 per cent (about 12 per cent after correction for crowding) with a nearly symmetric profile of 9.3 ± 0.6 h full width at half maximum. The Zwicky Transient Facility observed the star during the rise: +31.6 per cent in g, the brightest of 531 epochs in 7.6 yr, and +8.3 per cent in r. In the ZTF images the additional light coincides with the white dwarf to within about 0.3 arcsec. During the event, and only then, the TESS light curve contains a coherent oscillation with a period of 575.9 ± 0.3 s whose amplitude rises and falls with the brightening. The properties match the outbursts known in fewer than ten other cool DAVs. The search and the analysis were carried out with AI coding agents (OpenAI Codex; Anthropic Claude) under the author's direction, and a second AI system repeated the analysis independently from the raw archive files. The author is not a trained astronomer and no professional astronomer has reviewed the result. Section 7 of the manuscript states who did what and which results were reproduced. Files: the manuscript (PDF) and a package with the archive inputs, the re-analysis script that produces every number and figure of Section 4, and the working files of the search.