The F-, G-, K-, and M-type stars are the most abundant stellar population in the Milky Way and are expected to contribute to its diffuse X-ray emission. Yet their intrinsic average X-ray spectrum remains poorly constrained due to their faint X-ray luminosities, leaving their collective role in the X-ray background of the Milky Way uncertain. We aim to derive a distance-normalised average X-ray spectrum for nearby M dwarfs and F, G, and K stars and to characterise their ensemble spectral properties. We analysed the volume-complete sample of M dwarfs (M0–M6) and F, G, and K stars within 10 pc of the Sun using data from the all-sky survey aboard the Spectrum-Roentgen-Gamma (SRG) mission (eRASS: 4). Individual spectra were normalised by exposure and distance and then stacked to produce representative averages. From these spectra, we derived characteristic X-ray luminosities, which are helpful for estimating the contribution of late-type stars to the soft, diffuse X-ray emission of the Galaxy. The distance-normalised emission measures yield an average X-ray luminosity of (2. 6 erg/s for M-type stars, and (15 erg/s for F-, G-, and K-type stars in 0. 2--2. 0 keV. The 10-pc average spectra could be well described by a sum of three and two thermal models. The fitted temperatures and abundances remain consistent across M-star sub-groups, while early-M stars are, surprisingly, less luminous on average than mid-to-late-M types. These results offer new insights into the collective X-ray properties of nearby stars in the volume-complete context, and provide motivation to further explore the link with the unresolved soft X-ray background of the Galaxy. 10^ 27 10^ 27
Zheng et al. (Sun,) studied this question.