Binarity at Low Metallicity (BLOeM)

How does a metal-poor environment change the lives of massive binary stars? BLOeM tracks binary systems in the Small Magellanic Cloud (SMC) to learn about their multiplicity properties at a metallicity five times lower than that of the Milky Way.

BLOeM (T. Shenar) ADS
Binary fraction at different metallicities
Binary stars are more common in metal-poor places. For B-type stars the binary fraction rises from the Milky Way (solar metal content) to the LMC (~1/2 solar) and SMC (~1/5 solar). The line shows the best-fit trend with its uncertainty; red points are lower-mass stars for comparison; the purple line shows the trend for O-type stars.
Credit: From Villaseñor et al. (2025), A&A 698, A41

Overview

At low metallicity (few heavy elements), stellar winds are weaker and stars lose less mass. That changes how binary stars exchange matter, spin up, and eventually collapse—and it likely affects the kinds of compact-object pairs we see in gravitational waves.
BLOeM targets massive stars in the metal-poor Small Magellanic Cloud (SMC; ~1/5 the Milky Way’s metallicity) with repeated spectroscopy. We look for subtle shifts in spectral lines to reveal hidden companions, measure how common binaries are, and identify interaction products.

At a glance
• Role: Collaborator (PI: Tomer Shenar)
• Environment: SMC (low-Z)
• Telescope/instrument: VLT/FLAMES
• Awarded time: 116 hours • Method: Multi-epoch radial-velocity variability; stellar/orbital parameter
• Follow-up: OGLE photometry and targeted spectroscopy of key diagnostics (He II λ4686, Hα; ongoing)
• Goal: Map binary fractions and properties vs. metallicity and connect massive binaries to GW progenitors

My contributions

  • Contributed to observing proposals.
  • Analysis of RV variability for B-type dwarfs and giants.
  • First-author paper on the multiplicity of B-type dwarfs and giants.
  • Co-author on the first BLOeM paper and subsequent multiplicity papers.

Key results (so far)

  • B-type stars in the SMC show a binary fraction ≈80%, considerably higher than in the Milky Way—suggesting an anti-correlation between binary fraction and metallicity for massive stars for the first time (top figure, Villaseñor et al. 2025).

Publications

2025

  • J. I. Villaseñor; H. Sana; L. Mahy; T. Shenar; J. Bodensteiner; N. Britavskiy; D. J. Lennon; M. Moe; L. R. Patrick; M. Pawlak; and 24 authors (2025)
    Show all J. I. Villaseñor; H. Sana; L. Mahy; T. Shenar; J. Bodensteiner; N. Britavskiy; D. J. Lennon; M. Moe; L. R. Patrick; M. Pawlak; D. M. Bowman; P. A. Crowther; S. E. de Mink; K. Deshmukh; C. J. Evans; M. Fabry; M. Fouesneau; G. Holgado; N. Langer; J. Maíz Apellániz; I. Mandel; L. M. Oskinova; D. Pauli; V. Ramachandran; M. Renzo; H. -W. Rix; D. F. Rocha; A. A. C. Sander; F. R. N. Schneider; K. Sen; S. Simón-Díaz; J. Th. van Loon; S. Toonen; J. S. Vink
    Binarity at LOw Metallicity (BLOeM): Enhanced multiplicity of early B-type dwarfs and giants at Z = 0.2 Z⊙ — Astronomy and Astrophysics 698:A41. ADS arXiv DOI Cited 7
  • N. Britavskiy; L. Mahy; D. J. Lennon; L. R. Patrick; H. Sana; J. I. Villaseñor; T. Shenar; J. Bodensteiner; M. Bernini-Peron; S. R. Berlanas; and 25 authors (2025)
    Show all N. Britavskiy; L. Mahy; D. J. Lennon; L. R. Patrick; H. Sana; J. I. Villaseñor; T. Shenar; J. Bodensteiner; M. Bernini-Peron; S. R. Berlanas; D. M. Bowman; P. A. Crowther; S. E. de Mink; C. J. Evans; Y. Götberg; G. Holgado; C. Johnston; Z. Keszthelyi; J. Klencki; N. Langer; I. Mandel; A. Menon; M. Moe; L. M. Oskinova; D. Pauli; M. Pawlak; V. Ramachandran; M. Renzo; A. A. C. Sander; F. R. N. Schneider; A. Schootemeijer; K. Sen; S. Simón-Díaz; J. Th. van Loon; J. S. Vink
    Binarity at LOw Metallicity (BLOeM): Multiplicity of early B-type supergiants in the Small Magellanic Cloud — Astronomy and Astrophysics 698:A40. ADS arXiv DOI Cited 4
  • L. R. Patrick; D. J. Lennon; F. Najarro; T. Shenar; J. Bodensteiner; H. Sana; P. A. Crowther; N. Britavskiy; N. Langer; A. Schootemeijer; and 29 authors, including J. I. Villaseñor (2025)
    Show all L. R. Patrick; D. J. Lennon; F. Najarro; T. Shenar; J. Bodensteiner; H. Sana; P. A. Crowther; N. Britavskiy; N. Langer; A. Schootemeijer; C. J. Evans; L. Mahy; Y. Götberg; S. E. de Mink; F. R. N. Schneider; A. J. G. O'Grady; J. I. Villaseñor; M. Bernini-Peron; D. M. Bowman; A. de Koter; K. Deshmukh; A. Gilkis; G. González-Torà; V. M. Kalari; Z. Keszthelyi; I. Mandel; A. Menon; M. Moe; L. M. Oskinova; D. Pauli; M. Renzo; A. A. C. Sander; K. Sen; M. Stoop; J. Th. van Loon; S. Toonen; F. Tramper; J. S. Vink; C. Wang
    Binarity at LOw Metallicity (BLOeM): The multiplicity properties and evolution of BAF-type supergiants — Astronomy and Astrophysics 698:A39. ADS arXiv DOI Cited 8
  • J. Bodensteiner; T. Shenar; H. Sana; N. Britavskiy; P. A. Crowther; N. Langer; D. J. Lennon; L. Mahy; L. R. Patrick; J. I. Villaseñor; and 33 authors (2025)
    Show all J. Bodensteiner; T. Shenar; H. Sana; N. Britavskiy; P. A. Crowther; N. Langer; D. J. Lennon; L. Mahy; L. R. Patrick; J. I. Villaseñor; M. Abdul-Masih; D. M. Bowman; A. de Koter; S. E. de Mink; K. Deshmukh; M. Fabry; A. Gilkis; Y. Götberg; G. Holgado; R. G. Izzard; S. Janssens; V. M. Kalari; Z. Keszthelyi; J. Kubát; I. Mandel; G. Maravelias; L. M. Oskinova; D. Pauli; V. Ramachandran; D. F. Rocha; M. Renzo; A. A. C. Sander; F. R. N. Schneider; A. Schootemeijer; K. Sen; M. Stoop; S. Toonen; J. Th. van Loon; R. Valli; A. Vigna-Gómez; J. S. Vink; C. Wang; X. -T. Xu
    Binarity at LOw Metallicity (BLOeM): Multiplicity properties of Oe and Be stars — Astronomy and Astrophysics 698:A38. ADS arXiv DOI Cited 8

2024

  • T. Shenar; J. Bodensteiner; H. Sana; P. A. Crowther; D. J. Lennon; M. Abdul-Masih; L. A. Almeida; F. Backs; S. R. Berlanas; M. Bernini-Peron; and 68 authors, including J. I. Villaseñor (2024)
    Show all T. Shenar; J. Bodensteiner; H. Sana; P. A. Crowther; D. J. Lennon; M. Abdul-Masih; L. A. Almeida; F. Backs; S. R. Berlanas; M. Bernini-Peron; J. M. Bestenlehner; D. M. Bowman; V. A. Bronner; N. Britavskiy; A. de Koter; S. E. de Mink; K. Deshmukh; C. J. Evans; M. Fabry; M. Gieles; A. Gilkis; G. González-Torà; G. Gräfener; Y. Götberg; C. Hawcroft; V. Hénault-Brunet; A. Herrero; G. Holgado; S. Janssens; C. Johnston; J. Josiek; S. Justham; V. M. Kalari; Z. Z. Katabi; Z. Keszthelyi; J. Klencki; J. Kubát; B. Kubátová; N. Langer; R. R. Lefever; B. Ludwig; J. Mackey; L. Mahy; J. Maíz Apellániz; I. Mandel; G. Maravelias; P. Marchant; A. Menon; F. Najarro; L. M. Oskinova; A. J. G. O'Grady; R. Ovadia; L. R. Patrick; D. Pauli; M. Pawlak; V. Ramachandran; M. Renzo; D. F. Rocha; A. A. C. Sander; T. Sayada; F. R. N. Schneider; A. Schootemeijer; E. C. Schösser; C. Schürmann; K. Sen; S. Shahaf; S. Simón-Díaz; M. Stoop; S. Toonen; F. Tramper; J. Th. van Loon; R. Valli; L. A. C. van Son; A. Vigna-Gómez; J. I. Villaseñor; J. S. Vink; C. Wang; R. Willcox
    Binarity at LOw Metallicity (BLOeM): A spectroscopic VLT monitoring survey of massive stars in the SMC — Astronomy and Astrophysics 690:A289. ADS arXiv DOI Cited 25

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