Solar cycle variation in Sun-as-a-star Ca II 854.2 nm bisectors

TL;DR

This study investigates how the bisector shape of the Ca II 854.2 nm line varies with the solar cycle, revealing a correlation between bisector amplitude and solar activity, and supports their use in stellar magnetic studies.

Contribution

It demonstrates the solar cycle dependence of Sun-as-a-star Ca II 854.2 nm bisectors and discusses their potential in studying stellar convection and magnetic fields.

Findings

Bisector amplitude decreases during solar maximum.

Line core intensity is lower during solar minima.

Bisectors can be used to study convection-magnetic field relationships.

Abstract

The bisector of the strong chromospheric Ca II 854.2 nm line has an inverse-C shape the cause of which is not yet fully understood. We show that the amplitude of the bisector in Sun-as-a-star observations exhibits a solar cycle variation with smaller amplitudes during highest activity. The line core intensity is lower during solar minima while the part of the bisector most sensitive to the line core shows no systematic change with activity. Our results support the use of Ca II 854.2 nm bisectors in studying the relationship between convection and magnetic fields, not only in the Sun but in other stars as well.