Neon and oxygen in low activity stars: towards a coronal unification with the Sun

TL;DR

This study analyzes X-ray spectra of stars with varying activity levels to understand their neon-to-oxygen ratios, finding that low activity stars have ratios similar to the Sun, challenging the idea of an anomalously high neon abundance.

Contribution

It provides the first systematic investigation of Ne/O ratios across different stellar activity levels using high-resolution X-ray spectra.

Findings

Ne/O ratio correlates with stellar activity.

Low activity stars have Ne/O ratios similar to the Sun.

Enhanced neon abundance is unlikely to solve the solar modeling problem.

Abstract

The disagreement between helioseismology and a recent downward revision of solar abundances has resulted in a controversy about the true neon abundance of the Sun and other stars. We investigated XMM-Newton and Chandra high-resolution X-ray spectra of weakly and moderately active stars (log L_x/L_bol = -5...-7) and determined their coronal Ne/O abundance ratio by using two linear combinations of strong emission lines as well as a global-fitting method. The sample stars show a correlation between their Ne/O ratio and stellar activity in the sense that stars with a higher activity level show a higher Ne/O ratio. We find that the Ne/O ratio decreases in our sample from values of Ne/O~0.4 down to Ne/O~0.2, suggesting that ratios similar to 'classical' solar values are rather common for low activity stars. A significantly enhanced neon abundance as the solution to the solar modeling problem seems unlikely. We find no indications of a peculiar position of the Sun among other stars.