The effect of stellar activity on the LiI 6708, NaI 5896 and KI 7699 \AA lines: A comparison with the Pleiades, field stars and the Sun

TL;DR

This study models how stellar activity influences spectral lines and colors in late-type stars, explaining some observed variations in the Pleiades cluster and field stars, and highlighting activity's role in the lithium-rotation connection.

Contribution

It introduces an empirical analytical model that accounts for stellar spots and faculae effects on spectral lines and photometric colors, improving understanding of activity-related spectral variations.

Findings

Stellar activity partially explains the dispersion in Li I and K I equivalent widths.

The activity effects can account for some of the lithium-rotation correlation.

Only a small fraction of the observed spectral spread is due to activity effects.

Abstract

An analytical model has been developed to empirically study the effects of stellar spots and faculae on the observed equivalent widths of Li {\sc i} 6708, Na {\sc i} 5896 and K {\sc i} 7699 \AA lines (and abundances in the case of lithium) in late-type stars, taking into account the changes in the observed magnitudes and colors. Solar spectra corresponding to different active regions are used as input data and a range of filling factors are applied to simulate the surfaces of stars with different levels of activity. Detailed comparisons between predicted and observed photometric colors and equivalent widths are made for late-type stars of the Pleiades and the field. The observed dispersions in K {\sc i} and Li {\sc i} equivalent widths for Pleiades stars can be partially accounted by the simultaneous effects of activity on colors and the line formation, indicating that the lithium-rotation connection suggested for ~0.7-0.9 Msun Pleiades stars could be due in part to the stellar activity. However, under realistic values for the filling factors, only a small portion of the observed spread could be explained by these effects