Predicting photospheric UV emission from stellar evolutionary models

TL;DR

This paper introduces a simple method to estimate stellar photospheric UV emission for main-sequence stars using models and observational data, aiding in the study of stellar magnetic activity and exoplanet habitability.

Contribution

The authors develop a straightforward approach to derive stellar UV emission from models and observations, improving the assessment of stellar activity across different spectral types.

Findings

Photospheric UV contribution is less than 20% for M stars in NUV.

Photospheric UV contribution ranges from 10% to 70% for G stars.

Photospheric FUV emission is negligible for M stars and varies for other types.

Abstract

Stellar ultraviolet (UV) emission serves as a crucial indicator for estimating magnetic activity and evaluating the habitability of exoplanets orbiting stars. In this paper, we present a straightforward method to derive stellar photospheric UV emission for F to M main-sequence stars. By using PARSEC models, we establish relations between near-UV (NUV) and far-UV (FUV) magnitudes from the Galaxy Evolution Explorer (GALEX), NUV magnitudes from the China Space Station Telescope, and stellar effective temperatures and Gaia BP$-$RP color for different metallicities. Together with the observed sample, we find that for NUV emission, the photospheric contribution to the observed flux is less than 20% for M stars, around 10% to 70% for G stars, and ranges from 30% to 85% for G and F stars. For FUV emission, the photospheric contribution is less than $10^{-6}$ for M stars, below $10^{-4}$ for K stars, around $10^{-4}$ to 10% for G stars, and between 6% and 50% for F stars. Our work enables the simple and effective determination of stellar excess UV emission and the exploration of magnetic activity.