[astro-ph.EP] Atmospheric photochemical models incorporating the impacts of stellar flares often assume a ∼9,000 K spectrum at ultraviolet-optical wavelengths.
Recent multiwavelength observations, however, reveal a more complex picture with temperature measurements spanning 4,000-40,000 K, although the occurrence rates for flares with different temperatures remain unknown.
Here, we model the evolution of a Proterozoic Earth-like world with 0.01 bar of O2 under repeated flaring to identify the impact of flare effective temperatures. We explore four scenarios – two host star types (K2V and M2.5V) and two flare temperatures (9,000 K and 19,000 K) – selected to bound the potential parameter space.
The hotter flares have a larger impact on O3 photochemistry for both stellar types. M-star planetary atmospheres are more volatile and exhibit rapid changes in their O3 production and destruction rates. Meanwhile, K-star planetary atmospheres are more stable and are only impacted by the hottest flares, proving advantageous for biosignature searches.
We simulate 0.2-1.0 μm reflected light spectra for all four scenarios, and find that 19,000 K flares can result in either production or destruction of O3 depending on the host star spectral type increasing the 0.2 μm feature by ∼2× for the K2V star but decreasing it by 50% for the M2.5V star.
Future missions such as the EVE SMEX mission concept will provide robust flare temperature constraints for young FGKM stars, which will serve as inputs to improve photochemical models to inform future HWO observations.
Jaime S. Crouse, Nicholas F. Wogan, Ward S. Howard, Meredith A. MacGregor, Guadalupe Tovar Mendoza, Jacob Lustig-Yaeger, Evgenya L. Shkolnik
Comments: 17 pages, 7 figures, Submitted to AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2608.23548 [astro-ph.EP] (or arXiv:2608.23548v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.23548
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Submission history
From: Meredith MacGregor
[v1] Mon, 24 Aug 2026 17:50:42 UTC (3,375 KB)
https://arxiv.org/abs/2608.23548
Astrobiology, biosignature,
