Flare Hunting in Hot Subdwarf and White Dwarf Stars from Cycles 1–5 of TESS Photometry

Stellar flares are critical phenomena on stellar surfaces, which are closely tied to stellar magnetism. While extensively studied in main-sequence (MS) stars, their occurrence in evolved compact stars, specifically hot subdwarfs and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1–5...

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Bibliographic Details
Published in:The Astrophysical journal. Supplement series 2024-04, Vol.271 (2), p.57
Main Authors: Xing, Keyu, Zong, Weikai, Silvotti, Roberto, Fu, Jian-Ning, Charpinet, Stéphane, Cang, Tianqi, Hermes, J. J., Ma, Xiao-Yu, Wang, Haotian, Wang, Xuan, Wu, Tao, Wang, Jiaxin
Format: Article
Language:English
Subjects:
B subdwarf stars
Companion stars
Critical phenomena
Dwarf stars
Gas flaring
Hunting
Light curve
Machine learning
Magnetism
Photometry
Random Forests
Stars
Stellar evolution
Stellar flares
Stellar surfaces
Subdwarf stars
White dwarf stars
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Summary:Stellar flares are critical phenomena on stellar surfaces, which are closely tied to stellar magnetism. While extensively studied in main-sequence (MS) stars, their occurrence in evolved compact stars, specifically hot subdwarfs and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1–5 of TESS photometry, we conducted a pioneering survey of flare events in ∼12,000 compact stars, corresponding to ∼38,000 light curves with a 2 minute cadence. Through dedicated techniques for detrending light curves, identifying preliminary flare candidates, and validating them via machine learning, we established a catalog of 1016 flares from 193 compact stars, including 182 from 58 sdB/sdO stars and 834 from 135 WDs, respectively. However, all flaring compact stars showed signs of contamination from nearby objects or companion stars, preventing sole attribution of the detected flares. For WDs, it is highly probable that the flares originated from their cool MS companions. In contrast, the higher luminosities of sdB/sdO stars diminish companion contributions, suggesting that detected flares originated from sdB/sdO stars themselves or through close magnetic interactions with companions. Focusing on a refined sample of 23 flares from 13 sdB/sdO stars, we found their flare frequency distributions were slightly divergent from those of cool MS stars; instead, they resemble those of hot B/A-type MS stars having radiative envelopes. This similarity implies that the flares on sdB/sdO stars, if these flares did originate from them, may share underlying mechanisms with hot MS stars, which warrants further investigation.
ISSN:0067-0049
1538-4365
DOI:10.3847/1538-4365/ad2ddd