The effect of magnetic activity saturation in chromospheric flux-flux relationships

TL;DR

This study investigates how magnetic activity saturation affects chromospheric and coronal flux relationships in late-type dwarf stars, revealing deviations in certain star types linked to saturation and youth, impacting flux conversion methods.

Contribution

It provides the first quantification of deviations in dMe stars from flux-flux relations and links these deviations to magnetic saturation and stellar youth.

Findings

dMe stars deviate from general flux-flux relations

Stars with saturated X-ray emission also show saturation in Hα

Deviating stars are generally younger than those following the relations

Abstract

We present a homogeneous study of chromospheric and coronal flux-flux relationships using a sample of 298 late-type dwarf active stars with spectral types F to M. The chromospheric lines were observed simultaneously in each star to avoid spread due to long term variability. Unlike other works, we subtract the basal chromospheric contribution in all the spectral lines studied. For the first time, we quantify the departure of dMe stars from the general relations. We show that dK and dKe stars also deviate from the general trend. Studying the flux-colour diagrams we demonstrate that the stars deviating from the general relations are those with saturated X-ray emission and that those stars also present saturation in the H$\alpha$ line. Using several age spectral indicators, we show that they are younger stars than those following the general relationships. The non-universality of flux-flux relationships found in this work should be taken into account when converting between fluxes in different chromospheric activity indicators.