Long-term X-ray variability of the multiple-planet host L 98-59: Hints of an activity cycle
Year: 2025
Type: article
Abstract: High-energy irradiation in X-rays and UV (XUV) can transform the planetary atmospheres through photoevaporation and photochemistry. This is more crucial for M stars, whose habitable zones for Earth-like planets are located within a few percent of an AU. Transiting exoplanets around M dwarfs offer the opportunity to study their characteristics and habitability conditions. L 98-59 is an M3 dwarf hosting six Earth-like planets, with two of them in the habitable zone of the star. X-ray observations made in 2020 and 2021 detected significant flares above a quiescent luminosity of 4 − 10 × 10 26 erg s −1 . We present the results from two short XMM-Newton observations of L 98-59, which are part of a monitoring survey to detect long-term X-ray variability and activity cycles. In October 2024 the X-ray quiescent luminosity of the star was ∼5.9 × 10 25 erg s −1 , and it was about 6.3 × 10 26 erg s −1 in February 2025. We speculate that in late 2024 the star had a minimum of activity; in 2021 the star was near a maximum of an activity cycle, and in 2025 it was at the middle of the cycle. We suggest a coarse estimate of the period of ≈2 years and a peak-to-peak amplitude of about ≃10, which is the highest among the stars with a known X-ray cycle other than the Sun. We also infer that even the outer planet in the habitable zone, L 98-59, is exposed to an X-ray dose between 100 and 1600 times the X-ray irradiation of the Earth in the XUV band.
Source: Astronomy and Astrophysics
Institutions: Osservatorio Astronomico di Palermo, National Institute for Astrophysics, Leiden University, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Leiden Observatory, Université de Toulouse, University of Vienna, Université Paris Cité, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Aeronautics and Space Administration, European Commission, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Agenzia Spaziale Italiana, European Southern Observatory, Istituto Nazionale di Astrofisica, Nemzeti Kutatási Fejlesztési és Innovációs Hivatal, Ministero dell'Università e della Ricerca, European Research Council, National Research, Development and Innovation Office
OpenAlex ID: W4417004793