![Panel (a): HR diagram of the OC members with detections. The blue solid line is the fitting results of MS. green dashed lines represent the upper and lower bounds of the MS fitted with a ±0.5 offset, and the red dashed line is the same sequence shifted upwards by 2. The color bars represent the stellar ages. Panel (b): HR diagram of the field stars with detections. Panel (c): The Galactic distribution of the selected sources from the detected OC members. Panel (d): The Galactic distribution of the selected sources from the detected field stars. -- [astro-ph.SR]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/Evolution-of.png?fit=1200%2C678&ssl=1)
[astro-ph.SR] Stellar X-ray emission serves as a direct diagnostic of coronal activity, which is fundamentally linked to coronal heating processes. It also strongly influences the atmospheres and long-term habitability of orbiting exoplanets.
Investigating how this high-energy emission evolves is therefore essential for understanding the evolution of stellar magnetic dynamos and planetary atmospheres and habitability.
In this work, we investigate the evolution of X-ray activity and XUV irradiation for a sample of F-M dwarf stars based on Chandra and XMM-Newton observations. We find that F- and G-type stars broadly follow the traditional evolutionary picture of an early saturated (or weakly declining) phase followed by a modest decline, whereas K- and M-type stars exhibit a clear three-phase evolution of a saturated phase, an intermediate phase of rapid decay, and a final modest decline phase.
By combining X-ray, ultraviolet, and Ca II H&K bands, we show that coronal emission becomes increasingly dominant toward lower-mass stars. Based on the cumulative XUV emission calculated from our fitted relation, planets around F- and G-type stars experience relatively moderate XUV environments, while those around K- and M-type stars may exceed the empirical cosmic shoreline shortly after reaching the main sequence, though this conclusion depends on the adopted shoreline value.
Xue Li, Song Wang, Henggeng Han, Jun Ma, Yang Huang, Jifeng Liu
Comments: 22 pages, 16 figures, 3 tables. Accepted for publication in ApJS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2608.29248 [astro-ph.SR] (or arXiv:2608.29248v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2608.29248
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Submission history
From: Xue Li
[v1] Sat, 29 Aug 2026 13:07:36 UTC (4,016 KB)
https://arxiv.org/abs/2608.29248
Astrobiology,
