Binarity at LOw Metallicity (BLOeM)

Projected rotational velocities^★

¹ Instituto de Astrofísica de Canarias, C. Vía Láctea s/n 38205 La Laguna Santa Cruz de Tenerife, Spain
² Universidad de La Laguna, Dpto. Astrofísica, Av. Astrofśico Francisco Sánchez 38206 La Laguna Santa Cruz de Tenerife, Spain
³ Centro de Astrobiologìa (CSIC–INTA), Camino Bajo del Castillo s/n E-28692 Villanueva de la Cañada Madrid, Spain
⁴ Royal Observatory of Belgium Avenue Circulaire/Ringlaan 3 B-1180 Brussels, Belgium
⁵ Astrophysics Research Centre, School of Mathematics & Physics, Queen’s University Belfast BT7 1NN, UK
⁶ Argelander-Institut für Astronomie, Universität Bonn Auf dem Hügel 71 53121 Bonn, Germany
⁷ Max-Planck-Institute for Astrophysics Karl-Schwarzschild-Strasse 1 85748 Garching, Germany
⁸ Department of Astronomy, Pupin Hall, 538 West 120th Street Columbia University New York City NY 10027, USA
⁹ Astrophysics Research Cluster, School of Mathematical & Physical Sciences, University of Sheffield, Hicks Building Hounsfield Road Sheffield S3 7RH, UK
¹⁰ School of Chemical, Materials and Biological Engineering, University of Sheffield, Sir Robert Hadfield Building Mappin Street Sheffield S1 3JD, UK
¹¹ Armagh Observatory, College Hill Armagh BT61 9DG Northern Ireland, UK
¹² Anton Pannekoek Institute for Astronomy, University of Amsterdam Science Park 904 1098 XH Amsterdam, The Netherlands
¹³ The School of Physics and Astronomy, Tel Aviv University Tel Aviv 6997801, Israel
¹⁴ Institute of Astronomy, KU Leuven Celestijnenlaan 200D 3001 Leuven, Belgium
¹⁵ Max-Planck-Institut für Astronomie Königstuhl 17 D-69117 Heidelberg, Germany
¹⁶ Centro de Astrobiología (CSIC-INTA) Ctra. Torrejón a Ajalvir km 4 28850 Torrejón de Ardoz, Spain
¹⁷ School of Mathematics, Statistics and Physics, Newcastle University Newcastle upon Tyne NE1 7RU, UK
¹⁸ School of Physics and Astronomy, Monash University Clayton VIC 3800, Australia
¹⁹ Australian Research Council Centre of Excellence for Gravitational Wave Discovery Clayton VIC 3800, Australia
²⁰ European Space Agency (ESA), ESA Office, Space Telescope Science Institute 3700 San Martin Drive Baltimore MD 21218, USA
²¹ The Observatories of the Carnegie Institution for Science 813 Santa Barbara Street Pasadena CA 91101, USA
²² Department of Astronomy, California Institute of Technology Pasadena CA 91125, USA
²³ Astronomical Institute, Academy of Sciences of the Czech Republic Fričova 298 CZ-251 65 Ondřejov, Czech Republic
²⁴ Sterrenkundig Observatorium, Universiteit Gent Krijgslaan 281 S9 9000 Gent, Belgium
²⁵ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University Box 43 SE-221 00 Lund, Sweden
²⁶ Department of Astronomy & Steward Observatory 933 N. Cherry Ave. Tucson AZ 85721, USA
²⁷ Laboratório Nacional de Astrofísica Rua Estados Unidos 154 37504-364 Itajubá MG, Brazil
²⁸ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut Mönchhofstr. 12-14 69120, Heidelberg
²⁹ Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Universität Heidelberg Im Neuenheimer Feld 225 69120 Heidelberg, Germany
³⁰ School of Astronomy and Space Science, Nanjing University Nanjing 210023, PR China
³¹ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education Nanjing 210023, PR China
³² Tsung-Dao Lee Institute, Shanghai Jiao-Tong University 1 Lisuo Road Shanghai 201210, PR China

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 December 2025
Accepted: 25 January 2026

Abstract

The Binarity at LOw Metallicity (BLOeM) survey is an ESO large programme designed to obtain multi-epoch spectroscopy for 929 massive stars in the Small Magellanic Cloud (SMC). It will provide binary fractions and orbital configurations of binary systems and search for dormant black hole binary candidates (OB+BH). We present projected rotational velocities (v sin i) of all sources, and, using the multiplicity properties presented in previous papers, we derive the v sin i distributions of apparent single stars, single-lined spectroscopic (SB1) binaries, and SB2 systems. We identify a locus in the Hertzsprung-Russell diagram where rotational velocities decrease significantly; we interpret this feature as broadly corresponding to the terminal-age main sequence. The main-sequence cohort is distinguished by a broad range of v sin i values, but with a strong peak in the distribution in the range 30–60 km s⁻¹, which is close to the resolution limit of ∼30 km s⁻¹, indicating the presence of many upper limits. Sources in this low v sin i peak are distributed throughout the main sequence and are also present in the SB1 sample, though less prominent than in the single-star distribution. A preliminary analysis of the lowest v sin i cohort, which includes SB1 systems, implies that roughly one-third may be nitrogen rich, and we speculate that this cohort is a mix of pristine single stars, long-period binaries, and merger products. The SB2 systems appear to be mostly short-period binaries in synchronous rotation, and their v sin i estimates are distributed around a mean value of ∼140 km s⁻¹. Higher v sin i sources are also present in the single and SB1 systems, all of which have a tail to higher v sin i values. This is consistent with tidal and mass-transfer effects. The supergiants, with a few exceptions, have low v sin i, and the bulk of these systems is essentially unresolved at the current spectral resolution (∼30 km s⁻¹).