2025/11/14 by Maggio, Antonio, Pillitteri, Ignazio, Sanz-Forcada, Jorge +1
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · doi:10.48550/arxiv.2511.11220
openalex publication_date 2025/11/14 · openalex created_date 2025/11/18 · openalex updated_date 2026/07/28
High-energy emission spectra from the outer atmospheres of late-type stars represent an important feature of the stellar activity in several contexts, such as the photoevaporation and photochemistry of planetary atmospheres or the modeling of irradiated circumstellar disks in young objects. An accurate determination of these spectra in the EUV and soft X-ray (XUV) band requires high-resolution spectroscopy, that is rarely feasible with current instrumentation. We employed a relatively large set of plasma emission measure distributions (EMDs) as a function of temperature, derived from FUV and X-ray emission line spectra acquired with the Hubble Space Telescope and Chandra or XMM-Newton, in order to devise a relatively simple recipe for predicting EMDs and XUV spectra of stars of different spectral types, activity levels, and plasma metallicity. We show that the EMDs in the range of temperatures between 104 K and 107.5 K can be described using the stellar surface X-ray flux as a control parameter, but this parameterization also depends on the spectral type. In particular, we find that M-type stars show slightly lower emission measure at temperatures below ~105 K and higher emission measures for T > ~106.5 K with respect to FGK stars with similar surface X-ray fluxes. We evaluated the uncertainties in the broad-band EUV and X-ray fluxes derived from synthetic EMDs and spectra, considering in the error budget also the limited knowledge of the chemical abundances in stellar outer atmospheres.