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.

The similar to 60 000 solar-mass (M circle dot) star cluster R136 (NGC 2070) in the Tarantula Nebula in the Large Magellanic Cloud is the host of at least 55 massive stars (M >= 10M circle dot) which move away from the cluster at projected velocities >= 27.5 km/s. The origin of the high velocities of such runaway stars have been debated since the 1960s, resulting either from dynamical ejections or from supernova explosions. Because of the Gaia satellite's outstanding precision, we can now retrace the most recently ejected binary star, Mel 34, back to the center of R136 and reconstruct the events that 52 000 years ago led to its removal from R136; i.e., we establish its dynamical interaction and ejection history. We find that this ejection requires the participation of five stars in a strong interaction between a triple composed of the tight massive binary Mel 39, orbited by the star VFTS 590, and the binary star Mel 34. The participation of five stars is unexpected because runaway stars were not expected to result from triple interactions. The deterministic nature of the Newtonian dynamics in the scattering enables us to reconstruct the encounter that ejected Mel 34. We then predict that Mel 39 is a binary star with an 80M circle dot companion star that orbits within similar to 1 degrees in the same plane as Mel 34 and escapes the cluster with a velocity of similar to 64 km/s. The five stars will undergo supernova explosions in the coming 5 Myr at a distance of similar to 180-332 pc from their birth location (R136). The resulting black hole binaries, however, are not expected to merge within a Hubble time.

Given the uncertain evolutionary status of blue supergiant stars, their multiplicity properties hold vital clues to better understand their origin and evolution. As part of The Binarity at LOw Metallicity (BLOeM) campaign in the Small Magellanic Cloud, we present a multi-epoch spectroscopic survey of 128 supergiant stars of spectral type B5-F5, which roughly correspond to initial masses in the 6-30 M-circle dot range. The observed binary fraction for the B5-9 supergiants is 25 +/- 6% (10 +/- 4%) and 5 +/- 2% (0%) for the A-F stars, which were found using a radial-velocity (RV) variability threshold of 5 km s(-1) (10 km s(-1)) as a criterion for binarity. Accounting for observational biases, we find an intrinsic multiplicity fraction of less than 18% for the B5-9 stars and 8( -7)(+9) % for the AF stars, for the orbital periods up to 10(3.5) days and mass ratios (q) in the 0.1 < q < 1 range. The large stellar radii of these supergiant stars prevent short orbital periods, but we demonstrate that this effect alone cannot explain our results. We assessed the spectra and RV time series of the detected binary systems and find that only a small fraction display convincing solutions. We conclude that the multiplicity fractions are compromised by intrinsic stellar variability, such that the true multiplicity fraction may be significantly smaller. Our main conclusions from comparing the multiplicity properties of the B5-9- and AF-type supergiants to that of their less evolved counterparts is that such stars cannot be explained by a direct evolution from the main sequence. Furthermore, by comparing their multiplicity properties to red supergiant stars, we conclude that the AF supergiant stars are neither progenitors nor descendants of red supergiants.

Massive stars are predominantly born in stellar associations or clusters1. Their radiation fields, stellar winds and supernovae strongly impact their local environment. In the first few million years of a cluster's life, massive stars are dynamically ejected and run away from the cluster at high speed2. However, the production rate of dynamically ejected runaways is poorly constrained. Here we report on a sample of 55 massive runaway stars ejected from the young cluster R136 in the Large Magellanic Cloud. An astrometric analysis of Gaia data3-5 reveals two channels of dynamically ejected runaways. The first channel ejects massive stars in all directions and is consistent with dynamical interactions during and after the birth of R136. The second channel launches stars in a preferred direction and may be related to a cluster interaction. We found that 23-33% of the most luminous stars initially born in R136 are runaways. Model predictions2,6,7 have significantly underestimated the dynamical escape fraction of massive stars. Consequently, their role in shaping and heating the interstellar and galactic media and their role in driving galactic outflows are far more important than previously thought8,9.

The fraction of massive stars in young stellar clusters is of importance as they are the dominant sources of both mechanical and radiative feedback, strongly influencing the thermal and dynamical state of their birth environments. It turns out that a significant fraction of massive stars escape from their parent cluster via dynamical interactions of single stars and/or multiple stellar systems. M 17 is the nearest giant H II region hosting a very young and massive cluster: NGC 6618. Our aim is to identify stars brighter than G < 21 mag that belong to NGC 6618, including the (massive) stars that may have escaped since its formation, and to determine the cluster distance and age. We identified 42 members of NGC 6618 of which eight have a spectral type of O, with a mean distance of 1675 pc and a transversal velocity dispersion of about 3 km/s , and a radial velocity dispersion of 6 km/s. Another ten O stars are associated with NGC 6618, but they cannot be classified as members due to poor astrometry or high extinction. We have also identified six O star runaways. The relative transverse velocity of these runaways ranges from 10 to 70 km/s and their kinematic age ranges from about 100 to 750 kyr. Given the already established young age of NGC 6618 (< 1 Myr), this implies that massive stars are being ejected from the cluster already directly after or during the cluster formation process. When constructing the initial mass function, one has to take into account the massive stars that have already escaped from the cluster, that is, about 30% of the O stars of the original population of NGC 6618. The trajectories of the O runaways can be traced back to the central 0.25 pc region of NGC 6618. The good agreement between the evolutionary and kinematic age of the runaways implies that the latter provides an independent way to estimate (a lower limit to) the age of the cluster.

Context. Significant progress has been made toward understanding the formation of massive (M > 8 M-circle dot) binaries in close orbits (with periods of less than a month). Some of the observational studies leading to this progress are the detection of a very low velocity dispersion among the massive stars in the young region M17 and the measurement of a positive trend of velocity dispersion with age in Galactic clusters. The velocity dispersion observed in M17 could be explained either by the lack of binaries among the stars in this region, which implies the highly unlikely scenario of a different formation mechanism for M17 than for other Galactic regions, or by larger binary separations than typically observed, but with a binary fraction similar to other young Galactic clusters. The latter implies that, over time, the binary components migrate toward each other. This is in agreement with the finding that the radial velocity dispersion of young Galactic clusters correlates positively with their age. Aims. We aim to determine the origin of the strikingly low velocity dispersion by determining the observed and intrinsic binary fraction of massive stars in M17 through multi-epoch spectroscopy. Methods. We performed a multi-epoch spectroscopic survey consisting of three epochs separated by days and months, respectively. We complemented this survey with existing data covering timescales of years. We determined the radial velocity of each star at each epoch by fitting the stellar absorption profiles. The velocity shifts between epochs were used to determine whether a close companion is present. Results. We determined an observed binary fraction of 27% and an intrinsic binary fraction of 87%, consistent with that of other Galactic clusters. We conclude that the low velocity dispersion is due to a large separation among the young massive binaries in M17. Our result is in agreement with a migration scenario in which massive stars are born in binaries or higher-order systems at large separation and harden within the first million years of evolution. Such an inward migration may either be driven by interaction with a remnant accretion disk or with other young stellar objects present in the system, or by dynamical interactions within the cluster. Our results imply that possibly both dynamical interactions and binary evolution are key processes in the formation of gravitational wave sources.

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 circle dot). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods of P less than or similar to 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 & Aring; resolving power R = 6200; typical signal-to-noise ratio(S/N) approximate to 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 less than or similar to Teff/kK less than or similar to 45 and 3.7 < log L/L-circle dot < 6.1 and initial masses of 8 less than or similar to Mini less than or similar to 80 M-circle dot. 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.

Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as ``feedback''. Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates, and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting `Bringing Stellar Evolution and Feedback Together' in April 2022, and identify key areas where further dialogue can bring about radical changes in how we view the relationship between stars and the universe they live in.

In the first few Myr the massive stars dynamically interact, produce runaways and affect the initial binary population. Observing and interpreting the dynamics of young massive clusters is key to our understanding of the star formation process and predicting the outcome of stellar evolution. We have studied NGC6611 in the Eagle Nebula (M16), a young massive cluster hosting 19 O stars. We used Gaia EDR3 data to determine the membership, age, cluster dynamics and the kinematics of the massive stars including runaways. The membership analysis yields 137 members located at a mean distance of 1706 $\pm$ 7 pc. The colour - absolute magnitude diagram reveals a blue and a red population of pre-main-sequence stars, consistent with two distinct populations of stars. In line with earlier studies, the youngest population has a mean extinction $A_V$ = 3.6 $\pm$ 0.1 mag and an age = 1.3 $\pm$ 0.2 Myr, while the older population of stars has a mean extinction $A_V$ = 2.0 $\pm$ 0.1 mag and an age = 7.5 $\pm$ 0.4 Myr. The latter population is more spatially extended than the younger generation of stars. We argue that most of the OB stars belong to the younger population. We identify 8 runaways originating from the center of NGC6611, consistent with the dynamical ejection scenario. We show that ~ 50% of the O stars have velocities comparable to or greater than the escape velocity. These O stars can be traced back to the center of NGC6611 with kinematic ages ranging from 0 to 2 Myr. This suggests that dynamical interactions played an important role in the early evolution of NGC6611, which is surprising considering the low current stellar density. Comparing this to simulations of young massive clusters, the required initial radius of 0.1-0.5 pc is not consistent with that of NGC6611. The O stars could have initially formed in wide binaries and possibly harden through dynamical interactions.

Context. Young massive clusters provide the opportunity to study the outcome of the star formation process and the early evolution of star clusters. In the first few million years, the (massive) stars dynamically interact, producing runaways and affecting the initial (binary) population. Aims. Observing and interpreting the dynamics of young massive clusters is key to our understanding of the star formation process and predicting the outcome of stellar evolution, for example the number of gravitational wave sources. Methods. We have studied NGC 6611 in the Eagle Nebula (M16), a young massive cluster hosting ∼19 O stars. We used Gaia EDR3 data to determine the membership, age, cluster dynamics, and the kinematics of the massive stars including runaways. Results. The membership analysis yields 137 members located at a mean distance of 1706 ± 7 pc. The colour – absolute magnitude diagram reveals a blue and a red population of pre-main-sequence stars, consistent with two distinct populations of stars. In line with earlier studies, the youngest (reddest) population has a mean extinction of AV = 3.6 ± 0.1 mag and an age of 1.3 ± 0.2 Myr, while the older population of stars has a mean extinction of AV = 2.0 ± 0.1 mag and an age of 7.5 ± 0.4 Myr. The latter population is more spatially extended than the younger generation of stars. We argue that most of the OB stars belong to the younger population. We identify eight runaways originating from the centre of NGC 6611, consistent with the dynamical ejection scenario. Conclusions. We have studied the kinematics of the O stars in detail and show that ≳50% of the O stars have velocities comparable to or greater than the escape velocity. These O stars can be traced back to the centre of NGC 6611 with kinematic ages ranging from 0 to 2 Myr. These results suggest that dynamical interactions played an important role in the early evolution of NGC 6611, which is surprising considering the relatively low current stellar density (0.1–1 × 103 M⊙ pc−3). Comparing our results to simulations of young massive clusters, the initial radius of 0.1–0.5 pc (needed to produce the observed O star runaway fraction) is not consistent with that of NGC 6611. We propose a scenario where the O stars initially form in wide binaries or higher order systems and possibly harden through dynamical interactions.

ABSTRACT IGR J17285−2922 is a known X-ray binary with a low peak 2–10 keV X-ray luminosity of ∼ 1036 erg s−1 during outburst. IGR J17285−2922 exhibited two outbursts in 2003 and 2010 and went into outburst again in 2019. We have monitored this ∼ 4-month long 2019 outburst with Swift in X-ray and the Very Large Array in radio. We have also obtained four optical spectra with the Gran Telescopio Canarias and Southern Astrophysical Research Telescope, three optical photometry measurements with the Las Cumbres Observatory, and one near-infrared spectrum with the Gemini South telescope. The ratio between its X-ray and radio luminosity is consistent with both samples of neutron star and black hole (BH) X-ray binaries, while the ratio between the X-ray and optical luminosity is consistent with BH X-ray binaries. Studying the evolution of its X-ray power-law index throughout the outburst, we find additional evidence for a BH as compact object. The four optical spectra show no H α emission and the nIR spectrum shows no Brγ emission, suggesting that the donor star could be hydrogen-poor and hence that IGR J17285−2922 might have an ultracompact binary orbit. The shape of the X-ray light curve is well described by an exponential, followed by a linear decay, from which we obtain a relation between the orbital period Porb and the binary mass ratio. We discuss how this relation is consistent with theoretical predictions and known ultracompact X-ray binaries. Lastly, we discuss how the observed properties are reminiscent of short-Porb BH X-ray binaries.

Following the eROSITA discovery of the new X-ray transient SRGt J071522.1-191609 (ATel #13657) and the first follow-up observation using the X-ray telescope (XRT) on board the Neil Gehrels Swift Observatory (ATel #13661), we triggered an X-ray and radio monitoring program using Swift/XRT and the Karl G. Jansky Very Large Array (VLA).

IGR J17494-3030 is a transient X-ray binary that was recently reported to be in outburst by INTEGRAL (ATel #14119). Follow-up NICER observations have subsequently shown the presence of X-ray pulsations at 376 Hz (ATel #14124), confirming the neutron star nature of the compact object and identifying IGR J17494-3030 as an accreting millisecond X-ray pulsar (AMXP).