Low-luminosity Wolf-Rayet stars: a model-data comparison

TL;DR

This study compares low-luminosity Wolf-Rayet stars with stellar evolution models to test their internal mixing and mass-loss assumptions, highlighting the need for additional channels like binary interactions.

Contribution

It evaluates whether single-star evolutionary models can reproduce low-luminosity WR stars' properties, emphasizing the importance of mixing, mass-loss, and alternative formation channels.

Findings

Revised WR wind models help match faint WCL star luminosities.

WNC stars suggest additional mixing or binary stripping are needed.

Model-data comparison constrains stellar evolution parameters.

Abstract

A growing number of Galactic Wolf-Rayet (WR) stars, in particular WC and transitional WN/C (WNC) objects, have been reported at comparatively low luminosities. If confirmed, these low-luminosity WR stars provide stringent tests of stellar-evolution models, because their HR-diagram locations and surface compositions are highly sensitive to internal mixing and to the adopted WR-phase mass-loss history.We examine whether the HR-diagram positions and wind properties of low-luminosity WC/WNC stars can be reproduced by single-star evolutionary tracks at approximately solar metallicity, and we identify cases where additional channels (e.g. binary stripping) or dominant systematic uncertainties are likely required. Low-luminosity WNC/WC stars offer sensitive leverage on WR mixing and mass-loss prescriptions. A staged model-data comparison shows that revised WR winds can alleviate the luminosity-side tension for faint WCL stars, but the simultaneous requirements of temperature, surface composition, and WR-like wind density remain important. The WNC stars provide the strongest evidence that additional mixing, stripping, or binary-related channels may be required.