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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. We aim to estimate the binary fraction of a large sample of BSGs in the Small Magellanic Cloud within the Binarity at LOw Metallicity (BLOeM) survey. In total, we selected 262 targets with spectral types B0-B3 and luminosity classes I-II. This work is based on spectroscopic data collected by the GIRAFFE 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. 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 $\pm$ 3$\%$. 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., Comment: 18 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

Context. We need to understand the spin evolution of massive stars to compute their internal rotationally induced mixing processes, isolate effects of close binary evolution, and predict the rotation rates of white dwarfs, neutron stars and black holes. Aims. We discuss the spindown of massive main sequence stars imposed by stellar winds. Methods. We use detailed grids of single star evolutionary models to predict the distribution of the surface rotational velocities of core-hydrogen burning Galactic massive stars as function of their mass and evolutionary state. We then compare the spin properties of our synthetic populations with appropriately selected sub-samples of Galactic main sequence OB-type stars extracted from the IACOB survey. Results. We find that below $\sim 40 M_\odot$, observations and models agree in finding that the surface rotational velocities of Galactic massive stars remain relatively constant during their main sequence evolution. The more massive stars in the IACOB sample appear to spin down less than predicted, while our updated angular momentum loss prescription predicts an enhanced spindown. Furthermore, the observations show a population of fast rotators, with $v \sin I \gtrsim 200$ km/s persisting for all ages, which is not reproduced by our synthetic single star populations. Conclusions. We conclude that the wind-induced spindown of massive main sequence stars is yet to be fully understood, and that close binary evolution might significantly contribute to the fraction of rapid rotators in massive stars., Comment: 12 pages, 10 figures. Submitted to A&A

Rapidly rotating classical OBe stars have been proposed as the products of binary interactions, and the fraction of Be stars with compact companions implies that at least some are. However, to constrain the interaction physics spinning up the OBe stars, a large sample of homogeneously analysed OBe stars with well-determined binary characteristics and orbital parameters are required. We investigate the multiplicity properties of a sample of 18 Oe, 62 Be, and two Of?p stars observed within the BLOeM survey in the Small Magellanic Cloud. We analyse the first nine epochs of spectroscopic observations obtained over approximately three months in 2023. Radial velocities (RVs) of all stars are measured. Applying commonly-used binarity criteria we classify objects as binaries, binary candidates, and apparently single (RV stable) objects. We further inspect the spectra for double-lined spectroscopic binaries and cross-match with catalogues of X-ray sources and photometric binaries. We classify 14 OBe stars as binaries, and an additional 11 as binary candidates. The two Of?p stars are apparently single. Two more objects are most likely currently interacting binaries. Without those, the observed binary fraction for the OBe sample (78 stars) is f_OBe_obs=0.18+/-0.04 (f_obs_cand=0.32+/-0.05 including candidates). This fraction is less than half of that measured for OB stars in BLOeM. Combined with the lower fraction of SB2s, this suggests that OBe stars have indeed fundamentally different binary properties than OB stars. We find no evidence for OBe binaries with massive compact companions, in contrast to expectations from binary population synthesis. Our results support the binary scenario as an important formation channel for OBe stars, as post-interaction binaries may have been disrupted or the stripped companions of OBe stars are harder to detect., Comment: 12 pages (+appendix), 7 figures, accepted for publication in A&A

Massive stars play a very important role in many astrophysical fields. Yet, some fundamental aspects of their evolution remain poorly constrained. In this regard, there is an open debate on the width of the main-sequence (MS) phase. We aim to create an updated Hertzsprung-Russell (HR) diagram that includes a volume-limited and statistically significant sample of massive stars. Our goal is to use this sample to investigate the extension of the MS, including information about projected rotational velocities ($v\sin i$) and the spectroscopic binary status. We combine spectroscopic parameters derived with FASTWIND stellar atmosphere code and Gaia distances to obtain stellar parameters for 876 Galactic luminous O- and B-type stars gathered within the IACOB project. We use the ${\tt iacob-broad}$ tool to derive $v\sin i$ estimates and multi-epoch spectra to identify single/double-line spectroscopic binaries (SB1/SB2). We present an HR diagram for 670 stars located within 2500pc balancing completeness and number. We evaluate the extension of the MS in terms of the drop in the relative number of stars as a function of effective temperature ($T_{\rm eff}$). We find a consistent boundary at $\approx$22.5kK within the full range of luminosities that we use to delineate the terminal-age main sequence (TAMS). We obtain a smooth decrease of the highest $v\sin i$ with $T_{\rm eff}$ along the MS, likely limited by the critical velocity. We consider this effect combined with a lower expected fraction of stars beyond the MS as the best explanation for the lack of fast-rotating objects in the post-MS region. Our results favor low to mild initial rotation for the full sample and a binary past for the tail of fast-rotating stars. The prominence of SB1/SB2 systems in the MS, and the 25% decrease in the relative fraction of SB1 systems when crossing the TAMS can further delineate its location., Comment: 16 pages, 9 figures, accepted for publication in A&A