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

  • Binarity at LOw Metallicity (BLOeM): Projected rotational velocities D. J. Lennon; S. R. Berlanas; A. Herrero; N. Britavskiy; P. L. Dufton; N. Langer; H. Jin; A. Schootemeijer; A. Menon; J. Bestenlehner; and 29 authors, including J. Villasenor (2025) — arXiv: 2512.12102
    D. J. Lennon; S. R. Berlanas; A. Herrero; N. Britavskiy; P. L. Dufton; N. Langer; H. Jin; A. Schootemeijer; A. Menon; J. Bestenlehner; P. Crowther; J. S. Vink; J. Bodensteiner; T. Shenar; K. Deshmukh; J. Villasenor; L. Patrick; F. Najarro; A. de Koter; L. Mahy; D. M. Bowman; A. Bobrick; C. J. Evans; M. Gull; G. Holgado; Z. Katabi; J. Kubat; P. Marchant; D. Pauli; M. Pawlak; M. Renzo; D. F. Rocha; A. A. C. Sander; T. Sayada; S. Simon-Diaz; M. Stoop; R. Valli; C. Wang; X.-T. Xu
    ADS arXiv DOI
  • The binary landscape of massive stars at low $Z$: Insights from the BLOeM Campaign J. I. Villaseñor; H. Sana; J. Bodensteiner; N. Britavskiy; L. R. Patrick; T. Shenar; the BLOeM Collaboration (2025) — arXiv: 2511.08675 ADS arXiv DOI
  • Binarity at LOw Metallicity (BLOeM): Enhanced multiplicity of early B-type dwarfs and giants at Z = 0.2 Z⊙ 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) — Astronomy and Astrophysics 698:A41
    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
    ADS arXiv DOI Cited 15
  • Binarity at LOw Metallicity (BLOeM): Multiplicity of early B-type supergiants in the Small Magellanic Cloud 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) — Astronomy and Astrophysics 698:A40
    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
    ADS arXiv DOI Cited 8
  • Binarity at LOw Metallicity (BLOeM): The multiplicity properties and evolution of BAF-type supergiants 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) — Astronomy and Astrophysics 698:A39
    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
    ADS arXiv DOI Cited 14
  • Binarity at LOw Metallicity (BLOeM): Multiplicity properties of Oe and Be stars 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) — Astronomy and Astrophysics 698:A38
    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
    ADS arXiv DOI Cited 13

2024

  • Binarity at LOw Metallicity (BLOeM): A spectroscopic VLT monitoring survey of massive stars in the SMC 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) — Astronomy and Astrophysics 690:A289
    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
    ADS arXiv DOI Cited 37

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