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Binarity at LOw Metallicity (BLOeM): A spectroscopic VLT monitoring survey of massive stars in the SMC

Shenar, T. ; Pawlak, M. LU and Willcox, R. (2024) In Astronomy and Astrophysics 690.
Abstract
Surveys in the Milky Way and Large Magellanic Cloud have revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, and therefore in conditions approaching those of the Early Universe, remain sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign, an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the Small Magellanic Cloud, allowing us to probe multiplicity in the lowest-metallicity conditions to date (Z = 0.2 Z⊙). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods of P ≲ 3 yr, (iii) dormant black-hole binary candidates... (More)
Surveys in the Milky Way and Large Magellanic Cloud have revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, and therefore in conditions approaching those of the Early Universe, remain sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign, an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the Small Magellanic Cloud, allowing us to probe multiplicity in the lowest-metallicity conditions to date (Z = 0.2 Z⊙). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods of P ≲ 3 yr, (iii) dormant black-hole binary candidates (OB+BH), and (iv) a legacy database of physical parameters of massive stars at low metallicity. Main sequence (OB-type) and evolved (OBAF-type) massive stars are observed with the LR02 setup of the GIRAFFE instrument of the Very Large Telescope (3960- 4570 Å resolving power R = 6200; typical signal-to-noise ratio(S/N) ≈70- 100). This paper utilises the first nine epochs obtained over a three-month time period. We describe the survey and data reduction, perform a spectral classification of the stacked spectra, and construct a Hertzsprung-Russell diagram of the sample via spectral-type and photometric calibrations. Our detailed classification reveals that the sample covers spectral types from O4 to F5, spanning the effective temperature and luminosity ranges 6.5 ≲ Teff/kK ≲ 45 and 3.7 < log L/L⊙ < 6.1 and initial masses of 8 ≲ Mini ≲ 80 M⊙. The sample comprises 159 O-type stars, 331 early B-type (B0- 3) dwarfs and giants (luminosity classes V- III), 303 early B-type supergiants (II- I), and 136 late-type BAF supergiants. At least 82 stars are OBe stars: 20 O-type and 62 B-type (13% and 11% of the respective samples). In addition, the sample includes 4 high-mass X-ray binaries, 3 stars resembling luminous blue variables, 2 bloated stripped-star candidates, 2 candidate magnetic stars, and 74 eclipsing binaries. © The Authors 2024. (Less)
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keywords
Binaries: general, Binaries: spectroscopic, Magellanic Clouds, Stars: massive, Astrophysics, Barium alloys, Barium compounds, Black holes, Flow visualization, Luminance, Photomapping, Binaries:general, Binarity, Condition, Massive stars, Metallicities, Spectral types, Stars: Be, Giant stars
in
Astronomy and Astrophysics
volume
690
article number
A289
publisher
EDP Sciences
external identifiers
  • scopus:85207450864
ISSN
0004-6361
DOI
10.1051/0004-6361/202451586
language
English
LU publication?
yes
id
3d017190-a6be-44bb-afe4-1a762d93350a
date added to LUP
2025-09-01 13:26:37
date last changed
2025-09-01 13:27:49
@article{3d017190-a6be-44bb-afe4-1a762d93350a,
  abstract     = {{Surveys in the Milky Way and Large Magellanic Cloud have revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, and therefore in conditions approaching those of the Early Universe, remain sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign, an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the Small Magellanic Cloud, allowing us to probe multiplicity in the lowest-metallicity conditions to date (Z = 0.2 Z⊙). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods of P ≲ 3 yr, (iii) dormant black-hole binary candidates (OB+BH), and (iv) a legacy database of physical parameters of massive stars at low metallicity. Main sequence (OB-type) and evolved (OBAF-type) massive stars are observed with the LR02 setup of the GIRAFFE instrument of the Very Large Telescope (3960- 4570 Å resolving power R = 6200; typical signal-to-noise ratio(S/N) ≈70- 100). This paper utilises the first nine epochs obtained over a three-month time period. We describe the survey and data reduction, perform a spectral classification of the stacked spectra, and construct a Hertzsprung-Russell diagram of the sample via spectral-type and photometric calibrations. Our detailed classification reveals that the sample covers spectral types from O4 to F5, spanning the effective temperature and luminosity ranges 6.5 ≲ Teff/kK ≲ 45 and 3.7 &lt; log L/L⊙ &lt; 6.1 and initial masses of 8 ≲ Mini ≲ 80 M⊙. The sample comprises 159 O-type stars, 331 early B-type (B0- 3) dwarfs and giants (luminosity classes V- III), 303 early B-type supergiants (II- I), and 136 late-type BAF supergiants. At least 82 stars are OBe stars: 20 O-type and 62 B-type (13% and 11% of the respective samples). In addition, the sample includes 4 high-mass X-ray binaries, 3 stars resembling luminous blue variables, 2 bloated stripped-star candidates, 2 candidate magnetic stars, and 74 eclipsing binaries. © The Authors 2024.}},
  author       = {{Shenar, T. and Pawlak, M. and Willcox, R.}},
  issn         = {{0004-6361}},
  keywords     = {{Binaries: general; Binaries: spectroscopic; Magellanic Clouds; Stars: massive; Astrophysics; Barium alloys; Barium compounds; Black holes; Flow visualization; Luminance; Photomapping; Binaries:general; Binarity; Condition; Massive stars; Metallicities; Spectral types; Stars: Be; Giant stars}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Binarity at LOw Metallicity (BLOeM): A spectroscopic VLT monitoring survey of massive stars in the SMC}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202451586}},
  doi          = {{10.1051/0004-6361/202451586}},
  volume       = {{690}},
  year         = {{2024}},
}