Peering into the Wolf-Rayet phenomenon through [WO] and [WC] stars

TL;DR

This study investigates the winds of [WR]-type stars across different mass ranges using spectral analysis, revealing consistent wind properties and sequences that enhance understanding of the WR phenomenon and inform stellar evolution models.

Contribution

It provides the first detailed spectral analysis of low-mass [WR] stars, establishing their wind properties and sequences, and compares them with massive WR stars to understand the universality of the WR phenomenon.

Findings

WC+[WC] and WO+[WO] stars form independent sequences in wind diagrams.

WR and [WR] stars follow a consistent mass-loss trend without breakdown at low wind optical depths.

All studied WR stars define fundamental sequences in wind efficiency and related parameters.

Abstract

Spectroscopic observations have shown for decades that the Wolf-Rayet (WR) phenomenon is ubiquitous among stars with different initial masses. Although much effort to understand the winds from massive WR stars has been presented in the literature, not much has been done for such type of stars in the low-mass range. Here we present an attempt to understand the winds from [WR]-type stars using results from spectral analyses with the full non-LTE stellar atmosphere code PoWR. These results are put into context with the properties of massive WR stars. We found that WC+[WC] stars and WO+[WO] stars create independent sequences in the mass-loss rate ($\dot{M}$) and modified wind momentum ($D_\mathrm{mom}$) versus luminosity ($L$) diagrams. Our analysis indicates that even when the winds of WR and [WR] stars become optically thin, there is no breakdown of the general mass-loss trend, contrary to the observed ``weak wind phenomenon'' in OB stars. We report that all WR-type stars studied here broadly define single sequences in the wind efficiency ($\eta$) versus transformed mass-loss rate ($\dot{M}_\mathrm{t}$), the $\dot{M}_\mathrm{t}$-$T_\mathrm{eff}$ diagram, and the $(L, T_\mathrm{eff}, \dot{M})$ space, which suggest these to be fundamental properties of the WR phenomenon (regardless of the mass range), at least for WR-type stars of the O and C sequences. Our analytical estimations could drive computations of future stellar evolution models for WR-type stars.