Frequency separation ratios do not suppress magnetic activity effects in solar-like stars

TL;DR

Magnetic activity significantly affects asteroseismic measurements of solar-like stars, and common surface effect suppression techniques do not mitigate these influences, leading to potential systematic uncertainties in stellar parameter estimation.

Contribution

This study demonstrates that frequency separation ratios do not suppress magnetic activity effects, highlighting the need for improved modelling to account for these influences in asteroseismic analysis.

Findings

Frequency separation ratios reflect magnetic activity cycles.

Magnetic activity impacts stellar parameter estimates.

Standard surface effect corrections are ineffective against magnetic influences.

Abstract

Magnetic activity effects are typically neglected in asteroseismic modelling of solar-type stars, presuming that these effects can be accounted for in the parametrisation of the surface effects. It was however demonstrated that magnetic activity can have a significant impact on the asteroseismic characterisation using both forward and inverse techniques. We investigated whether frequency separation ratios, which are commonly used to efficiently suppress surface effects, are also able to suppress magnetic activity effects. Based on GOLF and BiSON observations of the Sun-as-a-star, we performed asteroseismic characterisations using frequency separation ratios as constraints to measure the apparent temporal evolution of the stellar parameters and their correlation with the 10.7 cm radio flux. Frequency separation ratios do not suppress the effects of magnetic activity. Both $r_{01}$ and $r_{02}$ ratios exhibit a clear signature of the magnetic activity cycle. Consequently, when these ratios are employed as constraints in asteroseismic modelling, magnetic activity effects are propagated to the stellar characterisation. Additionally, most stellar parameters correlate with the activity cycle, unlike the direct fitting of individual frequencies. Magnetic activity effects significantly impact asteroseismic characterisation, regardless of whether forward modelling or inverse methods are used. Standard techniques to suppress surface effects have proven ineffective against magnetic activity influences and systematic uncertainties of 4.7%, 2.9%, and 1.0% should be considered for the stellar age, mass, and radius, respectively. In preparation for future space-based photometry missions, it is therefore essential to enhance our theoretical understanding of these effects and develop a modelling procedure capable of accounting for or efficiently suppressing them.