A simple model for spectroscopic analyses of active stars

TL;DR

This paper introduces a simple two-component spectroscopic model to account for activity-related inaccuracies in analyzing young active stars, improving the reliability of metallicity and abundance measurements.

Contribution

The study presents a novel, easy-to-implement model that explains and predicts systematic errors caused by stellar activity in spectroscopic analyses of young stars.

Findings

Predicted underestimation of [Fe/H] by up to 0.2 dex in active stars.

Predicted overestimation of microturbulence velocity by up to 0.7 km/s.

Model aligns with observed data on solar twins and can be integrated into existing spectroscopic tools.

Abstract

Spectroscopic analyses of young late-type stars suffer from systematic inaccuracies, typically under-estimating metallicities but over-estimating abundances of certain elements including oxygen and barium. Effects are stronger in younger and cooler stars, and recent evidence specifically indicates a connection to the level of chromospheric activity. We present here a two-component spectroscopic model representing a non-magnetic baseline plus a magnetic spot, and analyse the resulting synthetic spectra of young solar analogues using a standard spectroscopic technique. For a moderately active star with solar parameters and chromospheric activity index log R'_HK = -4.3 (~100 Myr), we predict that [Fe/H] is underestimated by 0.06 dex while v_mic is overestimated by 0.2 km/s; for higher activity levels we predict effects as large as 0.2 dex and 0.7 km/s. Predictions are in agreement with literature data on solar twins, and indicate that the model is a plausible explanation to the observed effects. The model is simple enough that it can be included in spectroscopic packages with only changes to the underlying spectrum synthesis modules, if a log R'_HK value is provided.