Chromospheric Activity in 55 Cancri: II. Theoretical Wave Studies versus Observations

TL;DR

This paper compares theoretical wave-based models of chromospheric heating in 55 Cancri with observations, finding that acoustic waves plus magnetic heating best explain the star's low activity levels.

Contribution

It introduces self-consistent, nonlinear, time-dependent wave models including both acoustic and magnetic flux tube waves for 55 Cancri and compares them with observed Ca II fluxes.

Findings

Acoustic heating models approximate observed fluxes at low activity levels.

Adding magnetic heating improves agreement with observations.

The models support a combination of wave heating mechanisms in 55 Cancri.

Abstract

In this study, we consider chromospheric heating models for 55 Cancri in conjunction with observations. The theoretical models, previously discussed in Paper I, are self-consistent, nonlinear and time-dependent ab-initio computations encompassing the generation, propagation, and dissipation of waves. Our focus is the consideration of both acoustic waves and longitudinal flux tube waves amounting to two-component chromosphere models. 55 Cancri, a K-type orange dwarf, is a star of low activity, as expected by its age, which also implies a relatively small magnetic filling factor. The Ca II K fluxes are computed (multi-ray treatment) assuming partial redistribution and time-dependent ionization. The theoretical Ca II H+K fluxes are subsequently compared with observations. It is found that for stages of lowest chromospheric activity the observed Ca II fluxes are akin, though not identical, to those obtained by acoustic heating, but agreement can be obtained if low levels of magnetic heating - consistent with the assumed photospheric magnetic filling factor - are considered as an additional component; this idea is in alignment with previous proposals conveyed in the literature.