Surface Chemistry Reveals Mass Transfer History in Massive Stars

• About 70% of massive stars are born in binary systems, making mass transfer from a companion during stellar evolution a common, if rarely observed, phenomenon.
• Researchers from the Max Planck Institutes have developed a technique to identify "lone" stars that previously gained mass from a vanished binary companion by analyzing surface CNO (carbon, nitrogen, and oxygen) abundances.
• This method allows scientists to reconstruct the stellar past, determining the mass and efficiency of material transfer, and helping explain how such interactions influence galactic evolution.

The Mechanism of Stellar Fingerprints

• Stars possess distinct internal compositions due to nuclear fusion; their cores are enriched in helium and nitrogen while depleted in carbon and oxygen.
• When mass transfer occurs, donor material from the companion's core accumulates on the surface of the accreting star.
• By plotting nitrogen-to-carbon and nitrogen-to-oxygen ratios on a CNO abundance diagram, researchers can distinguish these mass-gaining stars from solitary or donor stars.

Case Study: Gamma Columbae

• Previously thought to be an envelope-stripped star, Gamma Columbae was re-identified using this method as a mass gainer that consumed 0.8 solar masses from a companion.
• The analysis shows the star's envelope is composed of approximately 17% stripped matter, providing clear chemical evidence of its history.
• The technique was also applied to SN 1987A, allowing researchers to successfully reconstruct the masses of both stars involved in the merger prior to the supernova event.

Future Implications

• The study of massive star evolution will be further advanced by upcoming large-scale astronomical surveys, such as WEAVE and 4MOST, which will provide data on thousands of additional stars.