English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The majority of Wolf-Rayet (WR) stars represent the stripped cores of evolvedmassive stars who lost most of their hydrogen envelope. In low metallicityenvironments, such as the Small Magellanic Cloud (SMC), stellar winds areweaker and binary interaction is expected to dominate WR-star formation.However, the WR binary fraction appears to be ~40% at any metallicity. We usethe recently determined physical properties of the twelve known SMC WR stars toexplore their possible formation channels through comparisons with grids of SMCmodels, simulated with the detailed stellar evolution code MESA. These includemodels of rapidly rotating single stars, which experience (partial) chemicallyhomogeneous evolution (CHE). We find that CHE is not able to account for themajority of the SMC WR stars. However, the apparently single WN star SMC AB12and the double WR system SMC AB5 (HD 5980) appear consistent with this channel.We also analyze core helium burning stellar models assuming constant hydrogengradients in their envelopes. We find a dichotomy in the envelope hydrogengradients required to explain the observed temperatures of the SMC WR stars.Shallow gradients are found for the WR stars with O star companions, consistentwith binary models where mass transfer occurs early, which is in agreement withtheir binary properties. On the other hand, much steeper hydrogen gradients areinferred for the group of hot apparently single WR stars. Since the hydrogenprofiles in post main sequence models of massive stars become steeper withtime, we conclude that these stars have likely been stripped by a companionduring a phase of common envelope evolution. The companions, either mainsequence stars or compact objects, are expected to still be present. Acorresponding search might identify the first immediate double black holebinary progenitor with masses as high as those detected in GW150914.

Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution