Activity of TRAPPIST–1 analog stars observed with TESS

• Published in: Astronomy and astrophysics (Berlin) 2021-06, Vol.650, p.A138
• Main Authors: Seli, Bálint, Vida, Krisztián, Moór, Attila, Pál, András, Oláh, Katalin
• Format: Article
• Language: English
• Subjects: Extrasolar planets; Frequency distribution; Habitability; Light curve; Observatories; Photometry; Planet detection; Stars; Starspots; Stellar age; Stellar flares; Transit
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202040098

As more exoplanets are being discovered around ultracool dwarfs, understanding their magnetic activity and the implications for habitability is of prime importance. To find stellar flares and photometric signatures related to starspots, continuous monitoring is necessary, which can be achieved with spaceborne observatories such as the Transiting Exoplanet Survey Satellite (TESS). We present an analysis of TRAPPIST–1 analog ultracool dwarfs with TESS full-frame image photometry from the first two years of the primary mission. A volume-limited sample up to 50 pc is constructed consisting of 339 stars closer than 0.​ m 5 to TRAPPIST–1 on the Gaia color–magnitude diagram. We analyzed the 30 min cadence TESS light curves of 248 stars, searching for flares and rotational modulation caused by starspots. The composite flare frequency distribution of the 94 identified flares shows a power-law index that is similar to TRAPPIST–1 and contains flares up to E TESS  = 3 × 10 33 erg. Rotational periods shorter than 5 d were determined for 42 stars, sampling the regime of fast rotators. The ages of 88 stars from the sample were estimated using kinematic information. A weak correlation between rotational period and age is observed, which is consistent with magnetic braking.