| Issue |
A&A
Volume 674, June 2023
|
|
|---|---|---|
| Article Number | L12 | |
| Number of page(s) | 11 | |
| Section | Letters to the Editor | |
| DOI | https://doi.org/10.1051/0004-6361/202346818 | |
| Published online | 20 June 2023 | |
Letter to the Editor
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⋆
1
Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
e-mail: vramachandran@uni-heidelberg.de
2
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
3
Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85748 Garching bei München, Germany
4
Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
5
Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
Received:
4
May
2023
Accepted:
1
June
2023
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 (∼1.5 − 8 M⊙), 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 Mstripped ∼ 3 M⊙ and MBe ∼ 17 M⊙. Binary evolutionary tracks suggest an initial mass of Mini ≳ 12 M⊙ 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.
Key words: stars: massive / binaries: spectroscopic / stars: fundamental parameters / stars: emission-line / Be / stars: neutron / stars: early-type
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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