X-ray emission of F-type stars and its analogy with G-type stars

Abstract: We conducted a systematic spectral study for single F-type main-sequence (MS) stars without significant X-ray outbursts to investigate X-ray spectral properties such as temperature, emission measure (EM), and luminosity (Lx). To this end, 33 single stars with relatively rich X-ray photon statistics were selected by cross-matching large astronomical catalogs of the XMM-Newton source catalog and the Tycho-2 spectral type catalog. A positive correlation was found in the observed EM--EM-weighted temperature relationship as seen in late-type stars and it is also found in the relationship that our single F-type MS star samples have a plasma with an EM-weighted temperature of $\lesssim$1 keV and an EM of $\lesssim$10$^{53}$ cm$^{-3}$ corresponding to Lx of $\lesssim$10$^{30}$~erg~s$^{-1}$. These observational features for the single F-type MS stars are consistent with those of the single G dwarf stars, suggesting that there are no significant differences in their X-ray coronal properties. Additionally, the obtained relationship between the X-ray activity and the Rossby number reinforces this suggestion in the literature. Moreover, the upper bounds in EM and Lx were found to be unique signatures for single stars and not valid for binary stars. Our results suggest that the planetary evolution in terms of the X-ray properties around F-type MS stars can be understood by extending the frameworks developed for G-type stars.