Long-term X-ray variability of the multiple-planet host L 98-59: Hints of an activity cycle

I. Pillitteri; S. Bellotti; S. Benatti; S. Boro Saikia; A. García Muñoz; K. G. Kislyakova; A. Maggio; G. Micela; K. Vida; A. A. Vidotto

doi:10.1051/0004-6361/202555853

Long-term X-ray variability of the multiple-planet host L 98-59: Hints of an activity cycle

I. Pillitteri
, S. Bellotti
, S. Benatti
, S. Boro Saikia
, A. García Muñoz
, K. G. Kislyakova
, A. Maggio
, G. Micela
, K. Vida
, A. A. Vidotto

Department of Astrophysics

Publications: Contribution to journal › Article › Peer Reviewed

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 × 10²⁶ 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 × 10²⁵ erg s⁻¹, and it was about 6.3 × 10²⁶ 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.

Original language	English
Article number	L2
Journal	Astronomy and Astrophysics
Volume	705
DOIs	https://doi.org/10.1051/0004-6361/202555853
Publication status	Published - 1 Jan 2026

Funding

IP acknowledges support from Bando per il Finanziamento della Ricerca Fondamentale 2024 dell’Istituto Nazionale di Astrofisica(INAF). AM and GM acknowledge support from the European Union – NextGeneration EU through the grant n. 2022J7ZFRA – Exo-planetary Cloudy Atmospheres and Stellar High energy (Exo-CASH), funded by MUR–PRIN 2022,and the ASI–INAF agreement 2021-5-HH.2-2024. AAV acknowledges funding from the European Research Council (ERC) under the European Union’sHorizon 2020 research and innovation programme (grant agreement No 817540,ASTROFLOW) and funding from the Dutch Research Council (NWO), withproject number VI.C.232.041 of the Talent Programme Vici. KV acknowledgesthe support of the Hungarian National Research, Development and InnovationOffice (NKFIH) Élvonal grant KKP 143986. SB acknowledges funding by theDutch Research Council (NWO) under the project “Exo-space weather andcontemporaneous signatures of star-planet interactions” (with project numberOCENW.M.22.215 of the research programme “Open Competition Domain Science – M”). Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Based on observations collected at the European SouthernObservatory under ESO programs 1102.C-0339(A), 0102.C-0525 and 0102.D0483, 1102.C-0744, 1102.C-0958 and 1104.C-0350. This work made use of datafrom eROSITA, a joint German-Russian science mission with the support of theDeutsches Zentrum für Luft- und Raumfahrt (DLR).

Austrian Fields of Science 2012

103003 Astronomy
103004 Astrophysics

Keywords

planetary systems
stars: activity
stars: coronae
stars: individual: L 98-59
stars: low-mass

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10.1051/0004-6361/202555853

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@article{b3570d80e9e948569b3af2ebb8690a92,

title = "Long-term X-ray variability of the multiple-planet host L 98-59: Hints of an activity cycle",

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 × 1026 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 × 1025 erg s−1, and it was about 6.3 × 1026 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.",

keywords = "planetary systems, stars: activity, stars: coronae, stars: individual: L 98-59, stars: low-mass",

author = "I. Pillitteri and S. Bellotti and S. Benatti and \{Boro Saikia\}, S. and \{Garc{\'i}a Mu{\~n}oz\}, A. and Kislyakova, \{K. G.\} and A. Maggio and G. Micela and K. Vida and Vidotto, \{A. A.\}",

note = "Publisher Copyright: {\textcopyright} The Authors 2025.",

year = "2026",

month = jan,

day = "1",

doi = "10.1051/0004-6361/202555853",

language = "English",

volume = "705",

journal = "Astronomy and Astrophysics",

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TY - JOUR

T1 - Long-term X-ray variability of the multiple-planet host L 98-59

T2 - Hints of an activity cycle

AU - Pillitteri, I.

AU - Bellotti, S.

AU - Benatti, S.

AU - Boro Saikia, S.

AU - García Muñoz, A.

AU - Kislyakova, K. G.

AU - Maggio, A.

AU - Micela, G.

AU - Vida, K.

AU - Vidotto, A. A.

PY - 2026/1/1

Y1 - 2026/1/1

N2 - 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 × 1026 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 × 1025 erg s−1, and it was about 6.3 × 1026 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.

AB - 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 × 1026 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 × 1025 erg s−1, and it was about 6.3 × 1026 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.

KW - planetary systems

KW - stars: activity

KW - stars: coronae

KW - stars: individual: L 98-59

KW - stars: low-mass

UR - https://www.scopus.com/pages/publications/105025667735

U2 - 10.1051/0004-6361/202555853

DO - 10.1051/0004-6361/202555853

M3 - Article

AN - SCOPUS:105025667735

SN - 0004-6361

VL - 705

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - L2

ER -

Long-term X-ray variability of the multiple-planet host L 98-59: Hints of an activity cycle

Abstract

Funding

Austrian Fields of Science 2012

Keywords

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