Massive stars have a major impact on their environment in their host galaxy. Observational determinations of their physical parameters are required to better constrain evolutionary models. In this context, the binary system WR 25 whose dominant spectral type is that of a nitrogen sequence Wolf-Rayet star, is of particular interest. It exhibits the highest known hydrogen content among the Milky Way Wolf-Rayet stars, as well as additional absorption lines. It is most probably an object still on the main-sequence or close to leaving it. We acquired new high-resolution spectra of this extremely interesting object. We present an improved version of the SB1 orbital solution for the motion of the WN component. We confirm the detection of the previously reported probable O companion and definitively prove that it is indeed gravitationally bound to the WN star. A first SB2 solution is presented, and a mass-ratio WN/O of 2.02 +/- 0.36 is derived. Following a spectral disentangling procedure, we identify the companion as an O5(f^+) star belonging to either the main-sequence (V) or giant (III) luminosity classes. The spectral type of the companion, together with the above-mentioned mass ratio, points to a very massive primary WN star of at least 55 solar masses. This confirms that WR 25 belongs to the family of very massive WNLh objects, a very poorly populated class in the Milky Way. We demonstrate that the absorption component in the P-Cygni profile of the He II lambda 4859 line of WR 25 is mainly due to the O-type companion, and we propose to adopt a WN6ha spectral type for the WN component of the system. On the basis of the extracted disentangled spectra, we derive approximate physical parameters through a detailed CMFGEN analysis, given the difficulty in constraining both the extinction towards WR 25 and the definitive brightness ratio between the components.

τ Canis Majoris (CMa) is an intriguing system that has captured astronomers' attention for more than a century. The two main components Aa and Ab are two evolved O stars on a 350 years orbit. Aa is itself a SB1 with a 155-days period and a 0.3 eccentricity. Since Hipparcos, we know that a 1.28-days period eclipsing binary (EB) is hidden somewhere in Aa or Ab, but nowhere else. Our recent analysis finally disentangles the system. We calculated the visual Aa-Ab orbit from AstraLux imaging. We detected the SB2 nature of Aa based on STIS spectra, the companion of the O star (Aa1) being a B+B binary (Aa2 = Aa2a + Aa2b). Multiple lines of evidence point towards Aa2 being the EB: time delays in the eclipsing orbit detected by TESS, high mass for Aa2 from SB1 from constraints from the orbit of Aa1, and a lack of radial-velocity motion of Ab synchronised with the eclipsing orbit. This remains as a tentative conclusion pending further analysis. We detect secular changes in the SB1 orbit of Aa1 on a baseline longer than a century. At this stage, the effect is most likely caused by the change in velocity of the Aa center of mass due to the Aa-Ab visual orbit. Apsidal motion is most probably not the culprit.

Massive stars (those ≥8 solar masses at formation) have radiative envelopes that cannot sustain a dynamo, the mechanism that produces magnetic fields in lower-mass stars. Despite this, approximately 7% of massive stars have observed magnetic fields, the origin of which is debated. We used multi-epoch interferometric and spectroscopic observations to characterize HD 148937, a binary system of two massive stars. We found that only one star is magnetic and that it appears younger than its companion. The system properties and a surrounding bipolar nebula can be reproduced with a model in which two stars merged (in a previous triple system) to produce the magnetic massive star. Our results provide observational evidence that magnetic fields form in at least some massive stars through stellar mergers.

When stars are gravitationally bound in a binary or higher order multiple system there is a chance they can interact, enabling mass and momentum transfer. Such interactions can be life-changing events for the stars involved as they can change their internal mixing, final mass and rotational speeds. In these proceedings, we describe our recent work which provides evidence that an interaction in a previous triple system caused a merger, the product of which is a magnetic star. This created the system as it is seen today – a massive binary system surrounded by an enriched ejecta nebula where only one of the massive stars is magnetic.

Context. Massive stars play a crucial role in the cosmic dynamics and chemical evolution of galaxies. Despite their significance, our understanding of their evolution and properties remains limited. An accurate determination of stellar parameters, such as the mass and radius, is essential for advancing our knowledge. Detached eclipsing binaries (DEBs) are particularly valuable for these determinations due to the minimal interaction between their stellar components, allowing for precise measurements. Aims. This study aims to introduce the Young Massive Detached Binary (YMDB) catalog, designed to address the gap in the high-precision absolute parameter determination for young massive stars. By focusing on DEBs within the spectral range O9-B1, this catalog seeks to provide a reliable database for future astronomical studies and improve our understanding of massive star evolution. Methods. We conducted a photometric analysis of 87 young massive stars in detached eclipsing systems using TESS light curves (LCs) that were processed through a custom pipeline. This analysis involved determining the amplitude of magnitude variations, orbital periods, times of minima, eccentricities, and the presence of apsidal motion and heartbeat phenomena. A thorough literature review was performed to obtain MK spectral classifications. We performed our own spectral classification of 19 systems to support the sample where a new classification was lacking or inconclusive. Results. The analysis identified 20 previously unreported binary systems, with 13 newly recognized as variable stars. Among the 87 stars examined, 30 are confirmed as YMDB members, and 25 are candidates pending spectral classification. The exclusion of the remaining 32 stars is attributed to unsuitable spectral types or their nondetached binary nature. Notable findings include the identification of new LC classifications, eccentricities in 13 systems, and heartbeat phenomena in several targets. Conclusions. The YMDB catalog offers a resource of high-quality LCs and reliable stellar classifications, serving as a valuable tool for the astronomical community.

ABSTRACT We present the first spectroscopic orbit of the O-type double-lined star HD 168112 A,B. We analyse 101 high-resolution optical spectra identifying the absorption lines of both components. The orbital solution presents a relatively long period, P = 513.52 ± 0.01 d, and a high eccentricity, e = 0.743 ± 0.005. The binary system consists of two very similar stars of minimum masses of ∼25 M⊙, effective temperatures of ∼40 000 K, and surface gravities of ∼3.7 dex. The system has a minimum semimajor axis a sin i ∼ 1000 R⊙. We confirm that the A and B visual components identified via interferometry do correspond to the spectroscopic ones. We also analyse the underlying stellar groups using Gaia DR3 data and ground-based spectroscopy as part of the Villafranca project, determining that NGC 6604 is at a distance of $1942^{+38}_{-36}$ pc and giving spectral classifications for 23 massive stellar systems in Villafranca O-035 and the surrounding Ser OB2 association, for which we provide the most complete census of massive stars to date.

ABSTRACT The evolution of massive stars is not completely understood. Several phenomena affect their birth, life, and death, multiplicity being one of them. In this context, the OWN and MONOS projects are systematically observing O- and WN-type stars whose multiplicity status is unknown. Their major goal considers the necessity of determining absolute parameters of massive stars. We have collected spectra of HD 93249 A and ALS 12502 A aiming at characterizing their binary nature. For both stars, we analysed high-resolution spectra and combined them with Transiting Exoplanet Survey Satellite (TESS) observations to be compared with binary models constructed by means of the phoebe code. We discovered that the radial velocity of HD 93249 A varies with a period of 2.97968 ± 0.00001 d and that the system presents ellipsoidal light variations. We disentangled the composite spectra and classified its components as O9 III and B1.5 III, respectively. Confirmed as a spectroscopic binary, HD 93249 A can no longer be used as spectral classification standard. ALS 12502 A turned out to be a detached eclipsing binary in the TESS and Gaia data. These results enable us to determine absolute parameters for each component in the system.

CONTEXT. The GOSSS spectral classifications and Gaia data have significantly improved our ability to measure distances and determine memberships of stellar groups with OB stars. AIMS. We have started a program to identify, measure distances, and determine the membership of Galactic stellar groups with OB stars. We start with the identification and distance determinations of groups with O stars. In this paper we concentrate on groups that contain stars with the earliest spectral subtypes. METHODS. We use GOSSS to select Galactic stellar groups with O2-O3.5 stars and a method that combines Gaia DR2 photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also include the two clusters in that paper to generate our first list of 16 O-type Galactic stellar groups. RESULTS. We derive distances, determine the membership, and analyze the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to O-016, including the 14 groups with the earliest-O-type optically-accessible stars known in the Milky Way. We compare our distance with previous results and establish that the best consistency is with VLBI parallaxes and the worst is with kinematic distances. Our results indicate that massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the Bajamar star in the North America nebula. This lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. We propose that HD 64 568 and HD 64 315 AB could have been ejected simultaneously from Villafranca O-012 S. Our results are consistent with a difference of approx. 20 microas in the Gaia DR2 parallax zero point between bright and faint stars. (ABRIDGED)

ABSTRACT Multiplicity is a ubiquitous characteristic of massive stars. Multiple systems offer us a unique observational constraint on the formation of high-mass systems. Herschel 36 A is a massive triple system composed of a close binary (Ab1-Ab2) and an outer component (Aa). We measured the orbital motion of the outer component of Herschel 36 A using infrared interferometry with the AMBER and PIONIER instruments of ESO’s Very Large Telescope Interferometer. Our immediate aims are to constrain the masses of all components of this system and to determine if the outer orbit is co-planar with the inner one. Reported spectroscopic data for all two components of this system and our interferometric data allow us to derive full orbital solutions for the outer orbit Aa-Ab and the inner orbit Ab1-Ab2. For the first time, we derive the absolute masses of mAa = 22.3 ± 1.7, mAb1 = 20.5 ± 1.5, and mAb2 = 12.5 ± 0.9 M⊙. Despite not being able to resolve the close binary components, we infer the inclination of their orbit by imposing the same parallax as the outer orbit. Inclinations derived from the inner and outer orbits imply a modest difference of about 22° between the orbital planes. We discuss this result and the formation of Herschel 36 A in the context of Core Accretion and Competitive Accretion models, which make different predictions regarding the statistic of the relative orbital inclinations.

ABSTRACT WR 21a was known as a massive spectroscopic binary composed of an O2.5 If*/WN6ha primary and an O3 V((f*))z secondary. Although a minimum value, the mass estimated for the primary placed it as one of the most massive stars found in our Galaxy. We report the discovery of photometric variations in the time series observations carried out by the Transiting Exoplanet Survey Satellite (TESS). These light variations are interpreted as formed by two main components: a sharp partial eclipse of the O3 secondary by the O2.5/WN6 star, and tidally excited oscillations. Based on the light minima, a new ephemeris for the system is calculated. The system configuration is detached and the observed eclipse corresponds to the periastron passage. During the eclipse, the light curve shape suggests the presence of the heartbeat effect. The frequencies derived for the tidally excited oscillations are harmonics of the orbital period. Combining new and previously published radial velocity measurements, a new spectroscopic orbital solution is also obtained. Using the phoebe code we model the TESS light curve and determine stellar radii of RO2.5/WN6 = 23.4 R⊙ and RO3 = 14.3 R⊙ and an orbital inclination i = 62${_{.}^{\circ}}$2 ± 0${_{.}^{\circ}}$9. The latter combined with the spectroscopic minimum masses lead to absolute masses of MO2.5/WN6 = 93.2 M⊙ and MO3 = 52.9 M⊙, which establishes WR 21a as belonging to the rare group of the very massive stars.

Context. Dynamical interactions in young stellar clusters can eject massive stars early in their lives and significantly alter their mass functions. If all of the most massive stars are lost, we are left with an orphan cluster. Aims. We study the Bermuda cluster (Villafranca O-014 NW), the most significant young stellar group in the North America and Pelican nebulae, and the massive stars that may have been ejected from it to test if it has been orphaned. Methods. We use Gaia EDR3 parallaxes and proper motions to search for walkaway and runaway stars in the vicinity of the North America and Pelican nebulae. The candidates are analyzed with a combination of spectroscopy and photometry to assess their nature and their trajectories are traced back in time to determine at what time they left the Bermuda cluster. Results. We detect three ejection events, dubbed the Bajamar, Toronto, and HD 201 795 events, which expelled (a minimum of) five, two, and two systems, respectively, or six, three, and three stars if we count the individual components in spectroscopic and eclipsing binaries. The events took place 1.611 ± 0.011 Ma, 1.496 ± 0.044 Ma, and 1.905 ± 0.037 Ma ago, respectively, but our analysis is marginally consistent with the first two being simultaneous. We detect bow shocks in WISE images associated with four of the ejected systems; their orientation agrees with that of their relative proper motions with respect to the cluster. Combining the three events, the Bermuda cluster has lost over 200 M⊙, including its three most massive stars, so it can be rightfully considered an orphan cluster. One consequence is that the present-day mass function of the cluster has been radically altered from its top-heavy initial value to one compatible with a Kroupa-like function. Another is that the cluster is currently expanding with a dynamical timescale consistent with the cause being the ejection events. A scenario in which the Bermuda cluster was formed in a conveyor-belt fashion over several hundreds of ka or even 1 Ma is consistent with all the observables.

Analysis of spectral line profile variations observed over 6 decades in the Wolf-Rayet system HD 5980 lead to the conclusion that Star A, the variable member of the system, has always dominated the wind collision zone (WCZ), contrary to suggestions that before 1994 the stronger wind belonged to its close companion, Star B. The observed variations are caused by a combination of physical occultations, wind eclipses and emission and absorption originating in the WCZ. The effects caused by the leading WCZ branch, which folds around Star B, are clearly seen as it crosses our line of sight to Star A during the secondary eclipse. These effects can inform on the WCZ velocity and density structures. We speculate that differences in line profiles at the same orbital phase but at different epochs may be linked to changes in the WCZ radiative properties. The 2017-2020 spectra indicate that HD 5980 was in a higher activity state than during 2010-2015.

ABSTRACT We present a new spectroscopic orbit of the O-type binary system HD 152147. We identify absorption lines in both components and use their radial velocities to determine the orbit, which results in a period of P = 50.2199 ± 0.0007 d, an eccentricity e = 0.738 ± 0.007, and a mean separation between the components of asin i = 151 ± 1 R⊙. Considering that the distance to the system is 1600 pc, this implies an angular separation of ∼0.44 mas, making it suitable for modern interferometric observations. In addition, we determine the fundamental stellar parameters of each component by means of a quantitative spectral analysis. We obtain Ma = 31.9−34.6 M⊙ and Ra = 17−24 R⊙ for the primary, and Mb = 14−15 M⊙ and Rb = 5−10 R⊙ for the secondary. We apply models with rotation to try to characterize the evolutionary status of the HD 152147 system. We find that the two components are compatible with a common age of 4.5 Myr. We also detect variations in the profile of Hα that are not modulated by the orbital cycle. Moreover, TESS photometry also presents intrinsic variability and was analysed for periodicities. We find a most relevant frequency of 20 times the orbital one, in a TESS data set that includes the periastron passage, and we interpret it as a tidally induced pulsation that seems to dissipate on a time-scale shorter than the orbital cycle because it is not present in another TESS data set that nearly covers the apoastron.

Stellar rotation is of key importance for the formation process, evolution, and final fate of massive stars. In this paper we review results from the study of the spin rate properties of a sample of more than 400 Galactic O-type stars surveyed by the IACOB and OWN projects. By combining vsini, Teff, and logg estimates (resulting from a detailed quantitative spectroscopic analysis) with information about the spectroscopic binarity status for an important fraction of the stars in the sample, we provide a renewed overview about how the empirical distribution of projected rotational velocities in the O-star domain depends on mass, evolutionary and binary status. The obtained distributions are then compared with predictions of several state-of-the-art evolutionary models for single stars, as well as from population synthesis simulations including binary interaction, and used to provide hints about the initial velocity distribution of stars with masses in the range ~15-80 Msol.

This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys.

At the time of this meeting, the latest Gaia data release is EDR3, published on 3 December 2020, but the next one, DR3, will appear soon, on 13 June 2022. This contribution describes, on the one hand, Gaia EDR3 results on massive stars and young stellar clusters, placing special emphasis on how a correct treatment of the astrometric and photometric calibration yields results that are simultaneously precise and accurate. On the other hand, it gives a brief description of the exciting results we can expect from Gaia DR3.

[ABRIDGED] AIMS: The MONOS project is collecting information and studying O-type spectroscopic binaries with delta>-20 deg. In this 2nd paper, we tackle the study of the 35 single-line spectroscopic binary (SB1) systems identified in the previous paper of the series (arXiv:1904.11385) by analyzing our data and reviewing the literature orbits of such systems. METHODS: We have measured the radial velocities for the ~700 spectra in our database using two different methods: Gaussian fitting for several diagnostic lines per object and cross-correlation using synthetic spectra. We also explored the TESS database and analyzed the light curves for 31 of the systems. RESULTS: We have confirmed 21 SB1 systems, discarded the binary nature of 6 stars (9 Sge, HD 192 281, HDE 229 232 AB, 68 Cyg, HD 108 and \alpha Cam), and left 6 stars as inconclusive due to lack of data. The remaining two stars are 15 Mon Aa which has been classified as SB2, and Cyg OB2-22 C, for which we find evidence that it is most likely a triple system where the O star is orbiting an eclipsing SB1. We have also recalculated 20 new orbital solutions, including the first spectroscopic orbital solution for V747 Cep. For Cyg OB2-22 C we have obtained new ephemerides but no new orbit.

Context. The OWN Survey has detected several O-type stars with composite spectra whose individual components show very different line broadening. Some of these stars have been revealed as binary systems whose components are asynchronous. This fact may be related to the processes acting in these systems (e.g., angular-momentum transfer, tidal forces, etc.) or to the origin of the binaries themselves. Aims. We aim to determine the orbital and physical parameters of the massive star HD 96264A in order to confirm its binary nature and to constrain the evolutionary status of its stellar components. Methods. We computed the spectroscopic orbit of the system based on the radial velocity analysis of 37 high-resolution, high-S/N, multi-epoch optical spectra. We disentangled the composite spectrum and determined the physical properties of the individual stellar components using FASTWIND models incorporated to the IACOB-GBAT tool. We also computed a set of evolutionary models to estimate the age of the system and explore its tidal evolution. Results. HD 96264A is a binary system composed of an O9.2 IV primary and a B0 V(n) secondary, with minimum masses of 15.0 ± 0.5 M ⊙ and 9.9 ± 0.4 M ⊙ , respectively, in a wide and eccentric orbit ( P = 124.336 ± 0.008 d; e = 0.265 ± 0.005). The primary and secondary components have different projected rotational velocities (∼40 and ∼215 km s −1 respectively), and the physical properties derived through quantitative spectroscopic analyses include masses of ∼20.5 M ⊙ and 16.8 M ⊙ , respectively. The evolutionary models indicate an approximate age of 4.5 Myr for both stars in the pair, corresponding to current masses and radii of 26.0 M ⊙ and 10.8 R ⊙ for the primary, and 17.9 M ⊙ and 7.0 R ⊙ for the secondary. Conclusions. The youth and wide orbit of the system indicate that the non-synchronous rotational nature of its components is a consequence of the stellar formation process rather than tidal evolution. This circumstance should be accounted for in theories of binary star formation.

[ABRIDGED] AIMS: The MONOS project is collecting information and studying O-type spectroscopic binaries with delta > -20 deg. In this 2nd paper, we tackle the study of the 35 single-line spectroscopic binary (SB1) systems identified in the previous paper of the series (arXiv:1904.11385) by analyzing our data and reviewing the literature orbits of such systems. METHODS: We have measured the radial velocities for the 700 spectra in our database using two different methods: Gaussian fitting for several diagnostic lines per object and cross-correlation using synthetic spectra. We also explored the TESS database and analyzed the light curves for 31 of the systems. RESULTS: We have confirmed 21 SB1 systems, discarded the binary nature of 6 stars (9 Sge, HD 192 281, HDE 229 232 AB, 68 Cyg, HD 108 and αCam), and left 6 stars as inconclusive due to lack of data. The remaining two stars are 15 Mon Aa which has been classified as SB2, and Cyg OB2-22 C, for which we find evidence that it is most likely a triple system where the O star is orbiting an eclipsing SB1. We have also recalculated 20 new orbital solutions, including the first spectroscopic orbital solution for V747 Cep. For Cyg OB2-22 C we have obtained new ephemerides but no new orbit.