The Decay of Stellar Dynamos and X-ray Activity

TL;DR

This study models the evolution of stellar X-ray activity by combining population synthesis with dynamo theory, testing predictions against new Chandra COSMOS observations to address conflicting prior conclusions.

Contribution

It introduces a comprehensive model integrating Galactic stellar populations with dynamo-driven X-ray emission, validated against recent observational data.

Findings

Model aligns approximately with observed X-ray luminosity distribution.

Spectral type distribution matches observational data.

Some discrepancies suggest gaps in understanding stellar X-ray emission.

Abstract

Existing stellar X-ray surveys suggest major problems in our understanding of the evolution of stellar magnetic activity in solar and late-type stars, reaching conflicting conclusions over the rate of decay of X-ray activity and the spectral types responsible. We are confronting these discrepancies with a new model of the expected stellar X-ray luminosity distribution, combining a Galactic population synthesis model with current theories for rotational spin- down and the rotation - activity relation for the stellar magnetic dynamo. Here we test our model using new observations of the stellar content of the Chandra COSMOS survey, for which 60 new stellar X-ray sources are identified from the thin disk and Galactic halo populations. Our model is in approximate agreement with the observed X-ray luminosity distribution and the distribution of spectral types responsible. However, slight differences in the form of the X-ray luminosity distribution exist that may hint at problems in our understanding of stellar X-ray emission.