The Coronal Temperatures of Low-Mass Main-Sequence Stars

TL;DR

This study establishes a universal scaling law linking the coronal temperature of low-mass main-sequence stars to their X-ray surface flux, based on extensive X-ray spectral data.

Contribution

It derives a new empirical scaling relation between coronal temperature and X-ray activity for low-mass stars using high-resolution spectral data.

Findings

Confirmed a universal Tcor-Fx relation for low-mass stars

Derived the formula Tcor=0.11 Fx^0.26 for coronal temperature

Validated the relation with high-resolution X-ray spectra

Abstract

Aims. We study the X-ray emission of low-mass main-sequence stars to derive a reliable general scaling law between coronal temperature and the level of X-ray activity. Methods. We collect ROSAT measurements of hardness ratios and X-ray luminosities for a large sample of stars to derive which stellar X-ray emission parameter is most closely correlated with coronal temperature. We calculate average coronal temperatures for a sample of 24 low-mass main-sequence stars with measured emission measure distributions (EMDs) collected from the literature. These EMDs are based on high-resolution X-ray spectra measured by XMM-Newton and Chandra. Results. We confirm that there is one universal scaling relation between coronal average temperature and surface X-ray flux, Fx, that applies to all low-mass main-sequence stars. We find that coronal temperature is related to Fx by Tcor=0.11 Fx^0.26, where Tcor is in MK and Fx is in erg/s/cm^2.