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arXiv · 2302.10376

Reconstructing the XUV Spectra of Active Sun-like Stars Using Solar Scaling Relations with Magnetic Flux

Kosuke Namekata·Shin Toriumi·Vladimir S. Airapetian·Munehito Shoda·Kyoko Watanabe·Yuta Notsu
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Abstract

Kepler Space Telescope and Transiting Exoplanet Survey Satellite unveiled that Sun-like stars frequently host exoplanets. These exoplanets are subject to fluxes of ionizing radiation in the form of X-ray and extreme-ultraviolet (EUV) radiation that may cause changes in their atmospheric dynamics and chemistry. While X-ray fluxes can be observed directly, EUV fluxes cannot be observed because of severe interstellar medium absorption. Here, we present a new empirical method to estimate the whole stellar XUV (X-ray plus EUV) and FUV spectra as a function of total unsigned magnetic fluxes of stars. The response of the solar XUV and FUV spectrum (0.1-180 nm) to the solar total unsigned magnetic flux is investigated by using the long-term Sun-as-a-star dataset over 10 yrs, and the power-law relation is obtained for each wavelength with a spectral resolution of 0.1-1 nm. We applied the scaling relations to active young Sun-like stars (G-dwarfs), EK Dra (G1.5V), $\pi^1$ Uma (G1.5V) and $\kappa^1$ Ceti (G5V), and found that the observed spectra (except for the unobservable longward EUV wavelength) are roughly consistent with the extension of the derived power-law relations with errors of an order of magnitude. This suggests that our model is a valuable method to derive the XUV/FUV fluxes of Sun-like stars including the EUV band mostly absorbed at wavelengths longward of 36 nm. We also discuss differences between the solar extensions and stellar observations at the wavelength in the 2-30 nm band and concluded that simultaneous observations of magnetic and XUV/FUV fluxes are necessary for further validations.

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Kosuke Namekata, Shin Toriumi, Vladimir S. Airapetian, Munehito Shoda, Kyoko Watanabe, Yuta Notsu. 2023-02-21. Reconstructing the XUV Spectra of Active Sun-like Stars Using Solar Scaling Relations with Magnetic Flux. https://doi.org/10.3847/1538-4357%2Facbe38

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