The average X-ray spectrum of the volume-complete M-, F-, G-, and K-type star sample within 10 pc of the Sun

Abstract

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 analysed the volume-complete sample of M- (M0--M6) and FGK-type stars within 10 pc of the Sun using data from eROSITA all-sky survey aboard the Spectrum-Roentgen-Gamma (SRG) mission (eRASS:4). Individual spectra were normalized by exposure and distance and stacked to produce representative averages. The distance-normalized emission measures yield an average X-ray luminosity of $(2.6\pm 0.1)\times 10^{27}$ erg/s for M-type stars, and $(15\pm 3)\times 10^{27}$ erg/s for F, G and K-type stars in 0.2--2.0 keV. The average spectra could be well described by a sum of three and two thermal models. Fitted temperatures and abundances remain consistent across M-star subgroups, while early-M stars are surprisingly on average less luminous than mid/late-M types. These results offer new insights into the collective X-ray properties of nearby stars, and provide motivation to explore the link with the unresolved soft X-ray background of the Galaxy.

22 pages, 13 figures. Accepted for publication in Astronomy & Astrophysics

References in corpus (10)

• The eROSITA X-ray telescope on SRG
• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• The 10 parsec sample in the Gaia era
• Relation of X-ray activity and rotation in M dwarfs and predicted time-evolution of the X-ray luminosity
• First eROSITA study of nearby M dwarfs and the rotation-activity relation in combination with TESS
• The Fifth Catalogue of Nearby Stars (CNS5)
• The Great Flare of 2021 November 19 on AD Leo. Simultaneous XMM-Newton and TESS observations
• The SRG/eROSITA diffuse soft X-ray background. I. The local hot bubble in the western Galactic hemisphere
• Complete X-ray census of Mdwarfs in the solar Neighborhood I. GJ 745 AB: Coronal-hole Stars in the 10 pc Sample

Cited by in corpus (1)

• X-ray luminous late-type giants: an overlooked population contributing to the Galactic ridge iron line emission