A partially stripped massive star in a Be binary at low metallicity: A missing link towards Be X-ray binaries and double neutron star mergers

V. Ramachandran*, J. Klencki, A. A.C. Sander, D. Pauli, T. Shenar, L. M. Oskinova, W. R. Hamann

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Standard binary evolutionary models predict a significant population of core helium-burning stars that lost their hydrogen-rich envelope after mass transfer via Roche-lobe overflow. However, there is a scarcity of observations of such stripped stars in the intermediate-mass regime (â ¼1.5â ââ 8â Mâ ), which are thought to be prominent progenitors of SN Ib/c. Especially at low metallicity, a significant fraction of these stars are expected to be only partially stripped, retaining a significant amount of hydrogen on their surfaces. For the first time, we discovered a partially stripped massive star in a binary with a Be-type companion located in the Small Magellanic Cloud (SMC) using a detailed spectroscopic analysis. The stripped-star nature of the primary is revealed by the extreme CNO abundance pattern and very high luminosity-to-mass ratio, which suggest that the primary is likely shell-hydrogen burning. Our target SMCSGS-FS 69 is the most luminous and most massive system among the known stripped star + Be binaries, with Mstrippedâ â ¼â 3â Mâ and MBeâ â ¼â 17âMâ . Binary evolutionary tracks suggest an initial mass of Miniâ â³â 12â Mâ for the stripped star and predict it to be in a transition phase towards a hot compact He star, which will eventually produce a stripped-envelope supernova. Our target marks the first representative of an as-yet-missing evolutionary stage in the formation pathway of Be X-ray binaries and double neutron star mergers.

Original languageEnglish
Article numberL12
JournalAstronomy and Astrophysics
Volume674
DOIs
StatePublished - 1 Jun 2023
Externally publishedYes

Funding

FundersFunder number
Baden-Württemberg Ministry of Science
Horizon 2020 Framework Programme
H2020 Marie Skłodowska-Curie Actions101024605
Deutsche Forschungsgemeinschaft445674056, SA4064/1-1
Bundesministerium für Bildung und Forschung
Deutsches Zentrum für Luft- und RaumfahrtFKZ 50OR2005
European Southern Observatory
International Space Science Institute512

    Keywords

    • Be
    • Binaries: spectroscopic
    • Stars: early-type
    • Stars: emission-line
    • Stars: fundamental parameters
    • Stars: massive
    • Stars: neutron

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