Coronal Loops with Different Metallicities and Generalized RTV Scaling Laws

Abstract

Stellar metallicity is a critical factor to characterize the stellar coronae because it directly affects the radiative energy loss from the atmosphere. By extending theoretical relations for solar coronal loops introduced by Rosner et al., we analytically derive scaling relations for stellar coronal loops with various metallicities. In order to validate the derived relations, we also perform magnetohydrodynamic simulations for the heating of coronal loops with different metallicities by changing radiative-loss functions according to the adopted elemental abundances. The simulation results nicely explain the generalized analytical scaling relations and show a strong dependence of the thermodynamical and radiative properties of the loops on metallicity. Higher density and temperature are obtained in lower-metallicity coronae because of the inefficient radiative cooling, provided that the surface condition is unchanged. Thus, it is estimated that the X-ray radiation from metal-poor coronae is higher because of their denser coronal gas. The generalized scaling laws can also be used as a tool to study the condition of high-energy radiation around magnetically active stars and their impact on planetary environments.

Effect of Magnetic Diffusion in the Chromosphere on the Solar Wind

“…We are presenting radiative and gravitational losses evaluated at r = r tc in Table 1, where the integration for L R is taken from r = r tc to r out . We note that L G,tc is exactly proportional to the density at r = r tc (see Equation (33)) and that L R practically includes the conductive loss, L c , because the downward conductive flux from the corona to the chromosphere radiates away (Rosner et al 1978;Washinoue & Suzuki 2023). Since the radiative cooling is proportional to ρ 2 in the optically thin corona (Equation ( 16)), a higher coronal The comparison between M0 and M3 indicates that the nonideal MHD effects reduce the mass-loss rate M  by a factor of 6.…”

Understanding the Duration of Solar and Stellar Flares at Various Wavelengths

“…In this work, we do not attempt to model variable elemental abundances, which would modify the radiative losses from a given loop and thus directly impact the duration of emission. This assumption also implies that flares from stars with metallicities different to the Sun would have different durations as loops would cool at different rates; that is, the cooling rates depend directly on the metallicity of the host star (Sutherland & Dopita 1993;Washinoue & Suzuki 2023). For instance, low metallicity stars such as ò Eridani (HD 22049; Santos et al 2004) show flares with longer duration than the Sun (Coffaro et al 2020).…”