Binarity at LOw Metallicity (BLOeM)

Multiplicity of early B-type supergiants in the Small Magellanic Cloud^⋆

¹ Royal Observatory of Belgium, Avenue Circulaire/Ringlaan 3, B-1180 Brussels, Belgium
² University of Liège, Allée du 6 Août 19c (B5C), B-4000 Sart Tilman, Liège, Belgium
³ Instituto de Astrofísica de Canarias, C. Vía Láctea, s/n, 38205 La Laguna, Santa Cruz de Tenerife, Spain
⁴ Universidad de La Laguna, Dpto. Astrofísica, Av. Astrofísico Francisco Sánchez, 38206 La Laguna, Santa Cruz de Tenerife, Spain
⁵ Centro de Astrobiología (CSIC-INTA), Ctra. Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain
⁶ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
⁸ The School of Physics and Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel
⁹ ESO – European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹⁰ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
¹¹ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
¹² Department of Physics & Astronomy, Hounsfield Road, University of Sheffield, Sheffield S3 7RH, United Kingdom
¹³ Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
¹⁴ European Space Agency (ESA), ESA Office, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁵ Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
¹⁶ Center for Computational Astrophysics, Division of Science, National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁸ School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
¹⁹ ARC Centre of Excellence for Gravitational-wave Discovery (OzGrav), Melbourne, Australia
²⁰ Department of Astronomy, 538 West 120th Street, Pupin Hall, Columbia University, New York City, NY 10027, USA
²¹ Department of Physics and Astronomy, University of Wyoming, 1000 E. University Ave., Dept. 3905, Laramie, WY 82071, USA
²² Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
²³ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 43 SE-221 00 Lund, Sweden
²⁴ Department of Astronomy & Steward Observatory, 933 N. Cherry Ave., Tucson, AZ 85721, USA
²⁵ Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
²⁶ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
²⁷ Lennard-Jones Laboratories, Keele University, Keele, Newcastle, ST5 5BG, UK
²⁸ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK

^⋆⋆ Corresponding author: mbritavskiy@uliege.be

Received: 11 November 2024
Accepted: 4 February 2025

Abstract

Context. The blue supergiant (BSG) domain contains a large variety of stars whose past and future evolutionary paths are still highly uncertain. Since binary interaction plays a crucial role in the fate of massive stars, investigating the multiplicity among BSGs helps shed light on the fate of such objects.

Aims. We aim to estimate the binary fraction of a large sample of BSGs in the Small Magellanic Cloud (SMC) within the Binarity at LOw Metallicity (BLOeM) survey. In total, we selected 262 targets with spectral types B0-B3 and luminosity classes I-II.

Methods. This work is based on spectroscopic data collected by the FLAMES instrument, mounted on the Very Large Telescope, which gathered nine epochs over three months. Our spectroscopic analysis for each target includes the individual and peak-to-peak radial velocity measurements, an investigation of the line profile variability, and a periodogram analysis to search for possible short- and long-period binaries.

Results. By applying a 20 km s⁻¹ threshold on the peak-to-peak radial velocities above which we would consider the star to be binary, the resulting observed spectroscopic binary fraction for our BSG sample is 23 ± 3%. An independent analysis of line profile variability reveals 11 (plus 5 candidates) double-lined spectroscopic binaries and 32 (plus 41 candidates) single-lined spectroscopic binaries. Based on these results, we estimated the overall observed binary fraction in this sample to be 34 ± 3%, which is close to the computed intrinsic binary fraction of 40 ± 4%. In addition, we derived reliable orbital periods for 41 spectroscopic binaries and potential binary candidates, among which there are 17 eclipsing binaries, including 20 SB1 and SB2 systems with periods of less than 10 days. We reported a significant drop in the binary fraction of BSGs with spectral types later than B2 and effective temperatures less than 18 kK, which could indicate the end of the main sequence phase in this temperature regime. We found no metallicity dependence in the binary fraction of BSGs, compared to existing spectroscopic surveys of the Galaxy and Large Magellanic Cloud.