This is the first paper of the “Binarity at LOw Metallicity (BLOeM)” collaboration which targets to obtain spectra for about 1000 massive stars in the SMC! Apart from being an extremely interesting project it really matches many of the sources I have been working with in the SMC. So perfect timing.
Binarity at LOw Metallicity (BLOeM): I. a spectroscopic VLT monitoring survey of massive stars in the SMC
Shenar, T. ; Bodensteiner, J. ; Sana, H. ; Crowther, P. A. ; Lennon, D. J. ; Abdul-Masih, M. ; Almeida, L. A. ; Backs, F. ; Berlanas, S. R. ; Bernini-Peron, M. ; Bestenlehner, J. M. ; Bowman, D. M. search by orcid ; Bronner, V. A. ; Britavskiy, N. ; de Koter, A. ; de Mink, S. E. ; Deshmukh, K. ; Evans, C. J. ; Fabry, M. ; Gieles, M. ; Gilkis, A. ; González-Torà, G. ; Gräfener, G. ; Götberg, Y. ; Hawcroft, C. ; Hénault-Brunet, V. ; Herrero, A. ; Holgado, G. ; Janssens, S. ; Johnston, C. ; Josiek, J. ; Justham, S. ; Kalari, V. M. ; Katabi, Z. Z. ; Keszthelyi, Z. ; Klencki, J. ; Kubát, J. ; Kubátová, B. ; Langer, N. ; Lefever, R. R. ; Ludwig, B. ; Mackey, J. ; Mahy, L. ; Maíz Apellániz, J. ; Mandel, I. ; Maravelias, G. ; Marchant, P. ; Menon, A. ; Najarro, F. ; Oskinova, L. M. ; Ovadia, R. ; Patrick, L. R. ; Pauli, D. ; Pawlak, M. ; Ramachandran, V. ; Renzo, M. ; Rocha, D. F. ; Sander, A. A. C. ; Sayada, T. ; Schneider, F. R. N. ; Schootemeijer, A. ; Schösser, E. C. ; Schürmann, C. ; Sen, K. ; Shahaf, S. ; Simón-Díaz, S. ; Stoop, M. ; van Loon, J. Th. ; Toonen, S. ; Tramper, F. ; Valli, R. ; van Son, L. A. C. ; Vigna-Gómez, A. ; Villaseñor, J. I. ; Vink, J. S. ; Wang, C. ; Willcox, R.
Surveys in the Milky Way and Large Magellanic Cloud 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, which approaches the conditions of the Early Universe, remains 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 SMC – the lowest metallicity conditions in which multiplicity is probed to date (Z = 0.2 Zsun). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods P < 3 yr, (iii) dormant OB+BH binaries, and (iv) a legacy database of physical parameters of massive stars at low metallicity. The stars are observed with the LR02 setup of the giraffe instrument of the Very Large Telescope (3960-4570A, resolving power R=6200; typical signal-to-noise ratio S/N=70-100). This paper utilises the first 9 epochs obtained over a three-month time. 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. 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/Lsun<6.1 and initial masses 8<Mini/Msun<80. It comprises 159 O-type stars, 324 early B-type (B0-3) dwarfs and giants (luminosity classes V-III), 309 early B-type supergiants (II-I), and 137 late-type supergiants. At least 75 stars are Oe/Be stars: 20 O-type and 55 B-type (13% and 10% of the respective samples). In addition, it includes four high-mass X-ray binaries, three stars resembling luminous blue variables, two bloated stripped-star candidates, two candidate magnetic stars, and 74 eclipsing binaries.
