# The Mg I b triplet and the 4571 {\AA} line as diagnostics of stellar chromospheric activity

## TL;DR

This study evaluates the diagnostic potential of the Mg I 4571 Å line and the b triplet for stellar chromospheric activity by analyzing their responses to atmospheric variations in solar-like stars.

## Contribution

It introduces a comprehensive atmospheric model grid to assess the sensitivity of these spectral lines to chromospheric activity indicators.

## Key findings

- Mg I 4571 Å line is sensitive to local atmospheric temperature changes.
- The b triplet lines show minimal response to atmospheric structure variations.
- Results support using the 4571 Å line as a chromospheric activity diagnostic.

## Abstract

Context. The Mg I 4571 {\AA} line and the b triplet are denoted in the literature as diagnostics of solar and stellar activity since their formation is in the low chromosphere. Aims. To investigate the potential of these four spectral lines as diagnostics of chromospheric activity in solar-like stars, studying the dependence of the intensity of these lines from local atmospheric changes by varying atmospheric models and stellar parameters. Methods. Starting with Next-Gen photospheric models, we build a grid of atmospheric models including photosphere, chromosphere and transition region and solve the radiative transfer to obtain synthetic profiles to compare with observed spectra of main-sequence, solar like stars with effective temperatures in the range 4800-6400 K, solar gravity and solar metallicity. Results. We find that the Mg I 4571 {\AA} line is significantly sensitive to local changes in the atmospheric model around the minimum temperature. Instead, the lines of the b triplet do not show significant responses to changes on the local atmospheric structure.