Habitable Zones

Evolution of Stellar Activity and Habitable zone: I. Ultraviolet Emission of Dwarfs in Open Clusters and Field Stars

By Keith Cowing

Status Report

astro-ph.SR

September 24, 2025

Filed under astro-ph.SR, astronomy, Circumstellar Habitable Zone, exoplanet, GALEX, Habitable Zone, radiation, space weathe, Spectroscopy

Evolution of Stellar Activity and Habitable zone: I. Ultraviolet Emission of Dwarfs in Open Clusters and Field Stars — Panel (a): H–R diagram of the open cluster members stars with GALEX observations. The blue solid line is the fitting results of main sequences. green dashed lines represent the upper and lower bounds of the main sequence fitted with a ±0.5 offset, and the red dashed lines is the same sequence shifted upwards by 2. Panel (b): H–R diagram of the field stars with GALEX observations. Panel (c): The galactic distribution of the selected sources from open clusters. The color bar represent the age of the stars. Panel (d): The galactic distribution of the selected sources from field stars. — astro-ph.SR

Near-ultraviolet (NUV) radiation from dwarf stars plays a critical role in shaping the habitability of planetary systems, yet its long-term evolution across different spectral types remains poorly investigated.

Based on GALEX NUV observations, we study the evolution of stellar NUV emission for a sample of 386,500 A- to M-type dwarfs spanning ages from 3 Myr to 10 Gyr, drawn from both open clusters and the field. The normalized NUV emission (fNUV/fJ) is used to trace the evolutionary trends.

Our results reveal distinct evolutionary pathways after considering the distance completeness: A and early-F dwarfs show a weak decline in NUV emission during the main-sequence phase; late-F to G dwarfs exhibit a clear decrease, consistent with continuous spin-down driven by magnetic braking; late-K and M-dwarfs undergo a rapid decline in NUV emission when they evolve from young stellar objects to main-sequence stars.

Furthermore, we construct the evolutionary tracks of stellar ultraviolet habitable zone (UHZ). By comparing stellar circumstellar habitable zone (CHZ) and UHZ, we find that G- and K-type stars offer the most stable overlap between thermal and UV habitability over long-term evolution.

Xue Li, Song Wang, Jun Ma, Henggeng Han, Yang Huang, Jifeng Liu

Comments: 23 pages, 16 figures, 3 tables. Accepted for publication in ApJS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.18559 [astro-ph.SR] (or arXiv:2509.18559v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2509.18559
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Submission history
From: Xue Li
[v1] Tue, 23 Sep 2025 02:33:46 UTC (21,291 KB)
https://arxiv.org/abs/2509.18559
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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