Suchergebnisse

Context. Multiplicity in massive stars is key to understanding the chemical and dynamical evolution of galaxies. Among massive stars, those of O type play a crucial role due to their high masses and short lifetimes. Aims: MONOS (Multiplicity Of Northern O-type Spectroscopic systems) is a project designed to collect information and study O-type spectroscopic binaries with ¿ > -20°. In this first paper we describe the sample and provide spectral classifications and additional information for objects with previous spectroscopic and/or eclipsing binary orbits. In future papers we will test the validity of previous solutions and calculate new spectroscopic orbits. Methods: The spectra in this paper have two sources: the Galactic O-Star Spectroscopic Survey (GOSSS), a project that obtains blue-violet R ¿ 2500 spectroscopy of thousands of massive stars, and LiLiMaRlin, a library of libraries of high-resolution spectroscopy of massive stars obtained from four different surveys (CAFÉ-BEANS, OWN, IACOB, and NoMaDS) and additional data from our own observing programs and public archives. We have also used lucky images obtained with AstraLux. Results: We present homogeneous spectral classifications for 92 O-type spectroscopic multiple systems and ten optical companions, many of them original. We discuss the visual multiplicity of each system with the support of AstraLux images and additional sources. For eleven O-type objects and for six B-type objects we present their first GOSSS spectral classifications. For two known eclipsing binaries we detect double absorption lines (SB2) or a single moving line (SB1) for the first time, to which we add a third system reported by us recently. For two previous SB1 systems we detect their SB2 nature for the first time and give their first separate spectral classifications, something we have also done for a third object just recently identified as a SB2. We also detect nine new astrometric companions and provide updated information on several others. We emphasize the results for two stars: for ¿ Ori AaAbB we provide spectral classifications for the three components with a single observation for the first time thanks to a lucky spectroscopy observation obtained close to the Aa,Ab periastron and for ¿1 Ori CaCb we add it to the class of Galactic Of?p stars, raising the number of its members to six. Our sample of O-type spectroscopic binaries contains more triple- or higher-order systems than double systems.© ESO 2019. ; Several authors acknowledge support from the Spanish Government Ministerio de Ciencia, Innovacion y Universidades through different grants: AYA2016-75931-C2-1/2-P (J.M.A., E.T.P., A.S., and E.J.A.), AYA2015-68 012-C2-1/2-P (E.T.P., I.N., S.S.-D., J.L., and A.M.), AYA2016-79 425-C3-2-P (J.A.C.), and SEV2015-0548 (S.S.-D.). R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program. R.H.B. and J.I.A. were also supported by the Direccion de Investigacion y Desarrollo de la Universidad de La Serena through projects PR18 143 and PR16 142, respectively. S.S.-D. acknowledges support from the Gobierno de Canarias grant ProID2017010115.

Context. The IACOB and OWN surveys are two ambitious, complementary observational projects which have made available a large multi-epoch spectroscopic database of optical high resolution spectra of Galactic massive O-type stars. Aims. Our aim is to study the full sample of (more than 350) O stars surveyed by the IACOB and OWN projects. As a first step towards this aim, we have performed the quantitative spectroscopic analysis of a subsample of 128 stars included in the modern grid of O-type standards for spectral classification. The sample comprises stars with spectral types in the range O3–O9.7 and covers all luminosity classes. Methods. We used the semi-automatized IACOB-BROAD and IACOB-GBAT/FASTWIND tools to determine the complete set of spectroscopic parameters that can be obtained from the optical spectrum of O-type stars. A quality flag was assigned to the outcome of the IACOB-GBAT/FASTWIND analysis for each star, based on a visual evaluation of how the synthetic spectrum of the best fitting FASTWIND model reproduces the observed spectrum. We also benefitted from the multi-epoch character of the IACOB and OWN surveys to perform a spectroscopic variability study of the complete sample, providing two different flags for each star accounting for spectroscopic binarity as well as variability of the main wind diagnostic lines. Results. We obtain – for the first time in a homogeneous and complete manner – the full set of spectroscopic parameters of the "anchors" of the spectral classification system in the O star domain. We provide a general overview of the stellar and wind parameters of this reference sample, as well as updated recipes for the SpT–Teff and SpT–log g calibrations for Galactic O-type stars. We also propose a distance-independent test for the wind-momentum luminosity relationship. We evaluate the reliability of our semi-automatized analysis strategy using a subsample of ~40 stars extensively studied in the literature, and find a fairly good agreement between our derived effective temperatures and gravities and those obtained by means of more traditional "by-eye" techniques and different stellar atmosphere codes. The overall agreement between the synthetic spectra associated with the IACOB-GBAT/FASTWIND best fitting models and the observed spectra is good for most of the analyzed targets, but 46 stars out of the 128 present a particular behavior of the wind diagnostic lines that cannot be reproduced by our grid of spherically symmetric unclumped models. These are potential targets of interest for more detailed investigations of clumpy winds and/or the existence of additional circumstellar emitting components contaminating the wind diagnostic lines (e.g., disks, magnetospheres). Last, our spectroscopic variability study has led to the detection of clear or likely signatures of spectroscopic binarity in 27% of the stars and small amplitude radial velocity variations in the photospheric lines of another 30%. Additionally, 31% of the investigated stars show variability in the wind diagnostic lines. ; This research is partially supported by the Spanish Government Ministerio de Economía y Competitivad (MINECO/FEDER) under grants AYA2015-68012-C1-1-P, AYA2015-68012-C2-2-P and SEV2015-0548. Financial support by the Spanish Ministerio de Ciencia e Innovación under the project AYA2008-06166-C03-01. J. M. A. acknowledges support from the Spanish Government Ministerio de Economía y Competitividad (MINECO) through grants AYA2013-40 611-P and AYA2016-75 931-C2-2-P. M. G. acknowledges funding by the Spanish MINECO via grants FIS2012-39162-C06-01, ESP2013-47809-C3-1-R and ESP2015-65597-C4-1-R. C. S.-S. acknowledges support from CONICYT-Chile through the FONDECYT Postdoctoral Project No. 3170778.

Context. The early-type binary MY Cam belongs to the young open cluster Alicante 1, embedded in Cam OB3. Aims. MY Cam consists of two early-O type main-sequence stars and shows a photometric modulation suggesting an orbital period slightly above one day. We intend to confirm this orbital period and derive orbital and stellar parameters. Methods. Timing analysis of a very exhaustive (4607 points) light curve indicates a period of 1.1754514 ± 0.0000015 d. High-resolution spectra and the cross-correlation technique implemented in the todcor program were used to derive radial velocities and obtain the corresponding radial velocity curves for MY Cam. Modelling with the stellar atmosphere code fastwind was used to obtain stellar parameters and create templates for cross-correlation. Stellar and orbital parameters were derived using the Wilson-Devinney code, such that a complete solution to the binary system could be described. Results. The determined masses of the primary and secondary stars in MY Cam are 37.7 ± 1.6 and 31.6 ± 1.4M⊙, respectively. The corresponding temperatures, derived from the model atmosphere fit, are 42 000 and 39 000 K, with the more massive component being hotter. Both stars are overfilling their Roche lobes, sharing a common envelope. Conclusions. MY Cam contains the most massive dwarf O-type stars found so far in an eclipsing binary. Both components are still on the main sequence, and probably not far from the zero-age main sequence. The system is a likely merger progenitor, owing to its very short period. ; This research is partially supported by the Spanish Ministerio de Economía y Competitividad under grant AYA2012-39364-C02-01/02, and the European Union.

On the basis of the Galactic O Star Spectroscopic Survey (GOSSS), we present a detailed systematic investigation of the O Vz stars. The currently used spectral classification criteria are rediscussed, and the Vz phenomenon is recalibrated through the addition of a quantitative criterion based on the equivalent widths of the He i λ4471, He ii λ4542, and He ii λ4686 spectral lines. The GOSSS O Vz and O V populations resulting from the newly adopted spectral classification criteria are comparatively analyzed. The locations of the O Vz stars are probed, showing a concentration of the most extreme cases toward the youngest star-forming regions. The occurrence of the Vz spectral peculiarity in a solar-metallicity environment, as predicted by the fastwind code, is also investigated, confirming the importance of taking into account several processes for the correct interpretation of the phenomenon. ; J.I.A. and R.H.B. acknowledge financial support from the Chilean Government grants, through the FONDECYT Iniciación 11121550 and FONDECYT Regular 1140076 projects, respectively. S.S.-D. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grants AYA2010-21697-C05-04, and Severo Ochoa SEV-2011-0187, and by the Canary Islands Government under support from [a] the Spanish Government Ministerio de Economía y Competitividad (MINECO) through grants AYA2010-15 081, AYA2010-17 631, and AYA2013-40 611-P and [b] the Consejería de Educación of the Junta de Andalucía through grant P08-TIC-4075. C.S.-S. acknowledges support from the Joint Committee ESO-Government of Chile. I.N. and A.M. acknowledge support from the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant AYA2012-39364-C02-02, and by the Generalitat Valenciana (ACOMP/2014/129). A.M. acknowledges support from the Generalitat Valenciana through the grant BEST/2015/242.

Context. The first Gaia Data Release (DR1) significantly improved the previously available proper motions for the majority of the Tycho-2 stars. Aims: We wish to detect runaway stars using Gaia DR1 proper motions and compare our results with previous searches. Methods: Runaway O stars and BA supergiants were detected using a 2D proper motion method. The sample was selected using Simbad, spectra from our GOSSS project, literature spectral types, and photometry processed using the code CHORIZOS. Results: We detect 76 runaway stars, 17 (possibly 19) of them with no prior identification as such, with an estimated detection rate of approximately one half of the real runaway fraction. An age effect appears to be present, with objects of spectral subtype B1 and later having traveled for longer distances than runaways of earlier subtypes. We also tentatively propose that the fraction of runaways is lower among BA supergiants that among O stars, but further studies using future Gaia data releases are needed to confirm this. The frequency of fast rotators is high among runaway O stars, which indicates that a significant fraction of them (and possibly the majority) is produced in supernova explosions. The spectral types in Table 2 will be added to the spectral types in the three GOSSS survey papers and in Maíz Apellániz et al. (2018 and the resulting table will be available from the GOSC web site http://gosc.cab.inta-csic.es.© ESO 2018 ; J.M.A., A.S., and E.T.P. acknowledge support from the Spanish Government Ministerio de Economia, Industria y Competitividad (MINECO/FEDER) through grant No. AYA2016-75931-C2-2-P. M.P.G. acknowledges support from the ESAC Trainee program. R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program. S.S.-D., I.N., and E.T.P. acknowledge support from the Spanish Government Ministerio de Economia, Industria y Competitividad (MINECO/FEDER) through grant No. AYA2015-68012-C2-1/2-P. ; Peer Reviewed

Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey that has collected, over a period of six years, spectra of ~105 stars. This survey provides not only the reduced spectra, but also the stellar parameters and abundances resulting from the analysis of the spectra. Aims. The GES dataflow is organised in 19 working groups. Working group 13 (WG13) is responsible for the spectral analysis of the hottest stars (O, B, and A type, with a formal cutoff of Teff > 7000 K) that were observed as part of GES. We present the procedures and techniques that have been applied to the reduced spectra in order to determine the stellar parameters and abundances of these stars. Methods. The procedure used was similar to that of other working groups in GES. A number of groups (called Nodes) each independently analyse the spectra via state-of-the-art techniques and codes. Specific for the analysis in WG13 was the large temperature range covered (Teff ≈ 7000–50 000 K), requiring the use of different analysis codes. Most Nodes could therefore only handle part of the data. Quality checks were applied to the results of these Nodes by comparing them to benchmark stars, and by comparing them to one another. For each star the Node values were then homogenised into a single result: the recommended parameters and abundances. Results. Eight Nodes each analysed part of the data. In total 17 693 spectra of 6462 stars were analysed, most of them in 37 open star clusters. The homogenisation led to stellar parameters for 5584 stars. Abundances were determined for a more limited number of stars. The elements studied are He, C, N, O, Ne, Mg, Al, Si, and Sc. Abundances for at least one of these elements were determined for 292 stars. Conclusions. The hot-star data analysed here, as well as the GES data in general, will be of considerable use in future studies of stellar evolution and open clusters. ; This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust ...

Context. Multiplicity in massive stars is key to understanding the chemical and dynamical evolution of galaxies. Among massive stars, those of O type play a crucial role due to their high masses and short lifetimes. Aims. MONOS (Multiplicity Of Northern O-type Spectroscopic systems) is a project designed to collect information and study O-type spectroscopic binaries with δ > −20°. In this first paper we describe the sample and provide spectral classifications and additional information for objects with previous spectroscopic and/or eclipsing binary orbits. In future papers we will test the validity of previous solutions and calculate new spectroscopic orbits. Methods. The spectra in this paper have two sources: the Galactic O-Star Spectroscopic Survey (GOSSS), a project that obtains blue-violet R ∼ 2500 spectroscopy of thousands of massive stars, and LiLiMaRlin, a library of libraries of high-resolution spectroscopy of massive stars obtained from four different surveys (CAFÉ-BEANS, OWN, IACOB, and NoMaDS) and additional data from our own observing programs and public archives. We have also used lucky images obtained with AstraLux. Results. We present homogeneous spectral classifications for 92 O-type spectroscopic multiple systems and ten optical companions, many of them original. We discuss the visual multiplicity of each system with the support of AstraLux images and additional sources. For eleven O-type objects and for six B-type objects we present their first GOSSS spectral classifications. For two known eclipsing binaries we detect double absorption lines (SB2) or a single moving line (SB1) for the first time, to which we add a third system reported by us recently. For two previous SB1 systems we detect their SB2 nature for the first time and give their first separate spectral classifications, something we have also done for a third object just recently identified as a SB2. We also detect nine new astrometric companions and provide updated information on several others. We emphasize the results for two stars: for σ Ori AaAbB we provide spectral classifications for the three components with a single observation for the first time thanks to a lucky spectroscopy observation obtained close to the Aa,Ab periastron and for θ1 Ori CaCb we add it to the class of Galactic Of?p stars, raising the number of its members to six. Our sample of O-type spectroscopic binaries contains more triple- or higher-order systems than double systems. ; Several authors acknowledge support from the Spanish Government Ministerio de Ciencia, Innovación y Universidades through different grants: AYA2016-75 931-C2-1/2-P (J.M.A., E.T.P., A.S., and E.J.A.), AYA2015-68 012-C2-1/2-P (E.T.P., I.N., S.S.-D., J.L., and A.M.), AYA2016-79 425-C3-2-P (J.A.C.), and SEV2015-0548 (S.S.-D.). R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program. R.H.B. and J.I.A. were also supported by the Dirección de Investigación y Desarrollo de la Universidad de La Serena through projects PR18 143 and PR16 142, respectively. S.S.-D. acknowledges support from the Gobierno de Canarias grant ProID2017010115.

Context. The formation, properties, and evolution of massive stars remain subject to considerable theoretical and observational uncertainty. This impacts on fields as diverse as galactic feedback, the production of cosmic rays, and the nature of the progenitors of both electromagnetic and gravitational wave transients. Aims. The young massive clusters many such stars reside within provide a unique laboratory for addressing these issues. In this work we provide a comprehensive stellar census of Westerlund 1 in order to to underpin such efforts. Methods. We employed optical spectroscopy of a large sample of early-type stars to determine cluster membership for photometrically-identified candidates, characterise their spectral type, and identify new candidate spectroscopic binaries. Results. Sixty nine new members of Westerlund 1 are identified via I-band spectroscopy. Together with previous observations, they illustrate a smooth and continuous morphological sequence from late-O giant through to OB supergiant. Subsequently, the progression bifurcates, with one branch yielding mid-B to late-F hypergiants, and cool supergiants, and the other massive blue stragglers prior to a diverse population of H-depleted WRs. We identify a substantial population of O-type stars with very broad Paschen series lines, a morphology that is directly comparable to known binaries in the cluster. In a few cases additional low-resolution R-band spectroscopy is available, revealing double-lined He I profiles and confirming binarity for these objects; suggesting a correspondingly high binary fraction amongst relatively unevolved cluster members. Conclusions. Our current census remains incomplete, but indicates that Westerlund 1 contains at least 166 stars with initial masses estimated to lie between ∼25 M⊙ and ∼50 M⊙, with more massive stars already lost to supernova. Our data is consistent with the cluster being co-eval, although binary interaction is clearly required to yield the observed stellar population, which is characterised by a uniquely rich cohort of hypergiants ranging from spectral type O to F, with both mass-stripped primaries and rejuvenated secondaries or merger products present. Future observations of Wd1 and similar stellar aggregates hold out the prospect of characterising both single- and binary- evolutionary channels for massive stars and determining their relative contributions. This in turn will permit the physical properties of such objects at the point of core-collapse to be predicted, which is of direct relevance for understanding the formation of relativistic remnants such as the magnetars associated with Wd1 and other young massive clusters. ; This research is partially supported by the Spanish Government under grants AYA2015-68012-C2-2-P and PGC2018-093741-B-C21 (MICIU/AEI/FEDER, UE), and made use of the SIMBAD database, operated at CDS, Strasbourg, France.

Context. Many massive stars have nearby companions. These hamper a characterization of massive stars through spectroscopy.Aims. We continue to obtain spatially resolved spectroscopy of close massive visual binaries to derive their spectral types.Methods. We used the lucky spectroscopy technique to obtain a large number of short long-slit spectroscopic exposures of 19 close visual binaries under good seeing conditions. We selected those with the best characteristics, extracted the spectra using multiple-profile fitting, and combined the results to derive spatially separated spectra. The results were analyzed in combination with data from lucky imaging, regular intermediate-resolution single-order spectroscopy, and echelle high-resolution spectroscopy.Results. The new application of lucky spectroscopy has allowed us (among other results) to [a] spatially disentangle two O stars (FN CMa B and 6 Cas B) with brighter BA supergiant companions for the first time; [b] determine that two B stars (alpha Sco B and HD 164 492 B) with close and more massive companions are fast rotators (in the second case, solving a case of mistaken identity); [c] extend the technique to cases with extreme magnitude differences (the previous two cases plus CS Cam A,B), shorter separations (HD 193 443 A,B), and fainter primary magnitudes down to B=11 (HD 219 460 A,B); [d] spatially disentangle the spectra of stars with companions as diverse as an A supergiant (6 Cas A), a Wolf-Rayet star (HD 219 460 B = WR 157), and an M supergiant (alpha Sco A); [e] discover the unexpected identity of some targets such as two previously unknown bright O stars (HD 51 756 B and BD +60 544) and a new member of the rare OC category (HD 8768 A); and [f] identify and classify (in some cases for the first time) which of the components of four visual binaries (sigma Ori, HD 219 460, HD 194 649, and HD 191 201) is a double-lined spectroscopic binary. For another seven systems (FN CMa, sigma Sco, HD 51 756, HD 218 195, HD 17 520, HD 24 431, and HD 164 492), we detect signs of spectroscopic binarity using high-spectral-resolution spectroscopy. We also determine the limits of the technique. © ESO 2021. ; J.M.A., C.F., A.S., M.P.G., and G.H. acknowledge support from the Spanish Government Ministerio de Ciencia through grant PGC2018-095049-B-C22. R.H.B. acknowledges support from the ESAC Faculty Visitor Program. I.N. and S.S.-D. acknowledge support from the Spanish Government Ministerio de Ciencia through grant PGC2018-093741-B-C21/22 (MICIU/AEI/FEDER, UE). S.S.-D. also acknowledges funding from the Spanish Government Ministerio de Ciencia through grants SEV 2015-0548 and CEX2019-000920-S, and from the Canarian Agency for Research, Innovation and Information Society (ACIISI), of the Canary Islands Government, and the European Regional Development Fund (ERDF), under grant with reference ProID2017010115. This paper is based on (a) lucky (and regular longslit) spectroscopy obtained with the 4.2m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos (ORM) on the island of La Palma, Spain; (b) lucky imaging obtained with the 2.2m Telescope at the Centro Astronomico Hispano en Andalucia (CAHA) in Almeria, Spain; (c) IFU spectroscopy obtained with the 2 m Liverpool Telescope (LT) at the Observatorio del Roque de los Muchachos (ORM) on the island of La Palma, Spain as part of GOSSS; (d) long-slit spectroscopy obtained with the 2.5 duPont Telescope at the Observatorio de Las Campanas (LCO) in Chile; and (e) high-resolution echelle spectroscopy from the LiLiMaRlin project obtained with a variety of spectrographs: HERMES at the 1.2 m Mercator Telescope (MT) at the Observatorio del Roque de los Muchachos (ORM) on the island of La Palma, Spain; ELODIE at the 1.93 m Observatoire de Haute-Provence (OHP) Telescope, France; FEROS at the 2.2 m Telescope of the Observatorio de La Silla in Chile; CAFE at the 2.2 m Centro Astronomico Hispano en Andalucia (CAHA) Telescope, Almeria, Spain; FIES at the 2.5 Nordic Optical Telescope (NOT) at the Observatorio del Roque de los Muchachos (ORM) on the island of La Palma, Spain; and UVES at the 8.2 m Kueyen Telescope at the Observatorio Paranal in Chile. Some of the MT and NOT data were obtained from the IACOB spectroscopic database (Simon-Diaz et al. 2011b,a, 2015b). This paper has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper has also made use of the Washington Double Star (WDS) catalog (Mason et al. 2001) and the Ski ff (2014) catalog of spectral classifications. The authors would like to thank the personnel of the WHT, CAHA, LT, LCO, MT, La Silla, and NOT observatories for their support and hospitality throughout the years. We dedicate this paper to our deceased colleagues, Virpi S. Niemela and Nolan R. Walborn, who they surely would have enjoyed having access to data like the ones presented here. ; With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709. ; Peer reviewed

Context. High-mass X-ray binaries (HMXBs) are exceptional astrophysical laboratories that offer a rare glimpse into the physical processes that govern accretion on compact objects, massive-star winds, and stellar evolution. In a subset of the HMXBs, the compact objects accrete matter solely from winds of massive donor stars. These so-called wind-fed HMXBs are divided in persistent (classical) HMXBs and supergiant fast X-ray transients (SFXTs) according to their X-ray properties. While it has been suggested that this dichotomy depends on the characteristics of stellar winds, they have been poorly studied. Aims. With this investigation, we aim to remedy this situation by systematically analyzing donor stars of wind-fed HMXBs that are observable in the UV, concentrating on those with neutron star (NS) companions. Methods. We obtained Swift X-ray data, HST UV spectra, and additional optical spectra for all our targets. The spectral analysis of our program stars was carried out with the Potsdam Wolf–Rayet model atmosphere code. Results. Our multi-wavelength approach allows us to provide stellar and wind parameters for six donor stars (four wind-fed systems and two OBe X-ray binaries). The wind properties are in line with the predictions of the line-driven wind theory. Based on the abundances, three of the donor stars are in an advanced evolutionary stage, while for some of the stars, the abundance pattern indicates that processed material might have been accreted. When passing by the NS in its tight orbit, the donor star wind has not yet reached its terminal velocity but it is still significantly slower; its speed is comparable with the orbital velocity of the NS companion. There are no systematic differences between the two types of wind-fed HMXBs (persistent versus transients) with respect to the donor stars. For the SFXTs in our sample, the orbital eccentricity is decisive for their transient X-ray nature. The dichotomy of wind-fed HMXBs studied in this work is primarily a result of the orbital configuration, while in general it is likely that it reflects a complex interplay between the donor-star parameters, the orbital configuration, and the NS properties. Based on the orbital parameters and the further evolution of the donor stars, the investigated HMXBs will presumably form Thorne–Żytkow objects in the future. ; The first author of this work (R.H.) is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/28-1. L.M.O. acknowledges support from the Verbundforschung grant 50 OR 1809. J.M.T. acknowledges the research grant ESP2017-85691-P. A.A.C.S. is supported by the Deutsche Forschungsgemeinschaft (DFG) under grant HA 1455/26. F.F., K.S., and A.B. are grateful for support from STScI Grant HST-GO-13703.002-A. T.S. acknowledges support from the European Research Council (ERC) under the European Union's DLV-772225-MULTIPLES Horizon 2020 research and innovation programme.

Context. Massive stars like company. However, low-mass companions have remained extremely di cult to detect at angular separations ( ) smaller than 1" (approx. 1000-3000 au considering typical distance to nearby massive stars) given the large brightness contrast between the companion and the central star. Constraints on the low-mass end of the companions mass-function for massive stars are however needed, for example to help distinguishing between various scenarios for the formation of massive stars. Aims. To obtain statistically significant constraint on the presence of low-mass companions beyond the typical detection limit of current surveys ( mag . 5 at . 1"), we initiated a survey of O and Wolf-Rayet stars in the Carina region using the SPHERE coronagraphic instrument on the VLT. In this first paper, we aim to introduce the survey, to present the methodology and to demonstrate the capability of SPHERE for massive stars using the multiple system QZ Car. Methods. We obtained VLT-SPHERE snapshot observations in the IRDIFS_EXT mode, which combines the IFS and IRDIS subsystems and simultaneously provides us four-dimension data cubes in two di erent field-of-view: 1.73" 1.73" for IFS (39 spectral channels across the YJH bands) and 12" 12" for IRDIS (two spectral channels across the K band). Angular- and spectral-di erential imaging techniques as well as PSF-fitting were applied to detect and measure the relative flux of the companions in each spectral channel. The latter are then flux-calibrated using theoretical SED models of the central object and are compared to a grid of ATLAS9 atmosphere model and (pre-)main-sequence evolutionary tracks, providing a first estimate of the physical properties of the detected companions. Results. Detection limits of 9 mag at > 200 mas for IFS and as faint as 13 mag at > 10:08 for IRDIS (corresponding to sub-solar masses for potential companions) can be reached in snapshot observations of only a few minutes integration times, allowing us to detect 19 sources around the QZ Car system. All but two are reported here for the first time. With near-IR magnitude contrasts in the range of 4 to 7.5 mag, the three brightest sources (Ab, Ad and E) are most likely physically bound, have masses in the range of 2 to 12 M and are potentially co-eval with QZ Car central system. The remaining sources have flux contrast of 1:5 105 to 9:5 106 ( K 11 to 13 mag). Their presence can be explained by the local source density and they are thus probably chance alignments. If they are members of the Carina nebula, they would be sub-solar-mass pre-main sequence stars. Conclusions. Based on this proof of concept, we showed that VLT/SPHERE allows us to reach the sub-solar mass regime of the companion mass function. This paves the way for this type of observation with a large sample of massive stars to provide novel constraints on the multiplicity of massive stars in a region of the parameter space that has remained inaccessible so far. ; European Southern Observatory 096.C-0510(A) French National Research Agency (ANR) ANR10 LABX56 FWO-Odysseus program G0F8H6N European Research Council under European Union's Horizon 2020 research programme 772225 European Research Council under European Union's Seventh Framework Program (ERC Grant) 337569 Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) BELgian federal Science Policy Office (BELSPO) through PRODEX grant Gaia BELgian federal Science Policy Office (BELSPO) through PRODEX grant PLATO Australian Research Council DP180104235

Context. Massive stars are a key element for understanding the chemical and dynamical evolution of galaxies. Stellar evolution is conditioned by many factors: Rotation, mass loss, and interaction with other objects are the most important ones for massive stars. During the first evolutionary stages of stars with initial masses (i.e., MZAMS) in the MZAMS ∼ 18–70 M⊙ range, they are of spectral type O. Given that stars in this mass range spend roughly 90% of their lifetime as O-type stars, establishing the multiplicity frequency and binary properties of O-type stars is crucial for many fields of modern astrophysics. Aims. The aim of the MONOS project is to collect information to study northern Galactic O-type spectroscopic binaries. In this second paper, we tackle the study of the 35 single-line spectroscopic binary (SB1) systems identified in the previous paper of the series, analyze our data, and review the literature on the orbits of the systems. Methods. We have measured ∼4500 radial velocities for a selection of diagnostic lines for the ∼700 spectra of the studied systems in our database, for which we have used two different methods: a Gaussian fit for several lines per object and cross-correlation with synthetic spectra computed with the FASTWIND stellar atmospheric code. We have also explored the photometric data delivered by the TESS mission to analyze the light curve (LC) of the systems, extracting 31 of them. We have explored the possible periods with the Lomb-Scargle method and, whenever possible, calculated the orbital solutions using the SBOP and GBART codes. For those systems in which an improved solution was possible, we merged our radial velocities with those in the literature and calculated a combined solution. Results. As a result of this work, of the 35 SB1 systems identified in our first paper we have confirmed 21 systems as SB1 with good orbits, discarded the binary nature of six stars (9 Sge, HD 192 281, HDE 229 232 AB, 68 Cyg, HD 108, and α Cam), and left six stars as inconclusive due to a 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. ; E.T.P., I.N.D. and S.S.D. acknowledge support from the Spanish Government Ministerio de Ciencia through grant AYA2015-68 012-C2-1/2-P. E.T.P. and J.M.A. acknowledge support from the Spanish Government Ministerio de Ciencia through grants AYA2016-75 931-C2-2-P and PGC2018-095 049-B-C22. R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program and ANID FONDECYT Project 1211903. G.H. acknowledges support from the Spanish Government Ministerio de Ciencia through grant PGC2018-95049-B-CC22 and ESA Contract No. 4000-126507/19/ES/CM. This research has made use of the SIMBAD database, operated at CDS (Strasbourg, France), NASA's Astrophysics Data System Bibliographic Services and the Python programming language (Python Software Foundation), Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration 2018).

Context. The first Gaia Data Release (DR1) significantly improved the previously available proper motions for the majority of the Tycho-2 stars. Aims. We wish to detect runaway stars using Gaia DR1 proper motions and compare our results with previous searches. Methods. Runaway O stars and BA supergiants were detected using a 2D proper motion method. The sample was selected using Simbad, spectra from our GOSSS project, literature spectral types, and photometry processed using the code CHORIZOS. Results. We detect 76 runaway stars, 17 (possibly 19) of them with no prior identification as such, with an estimated detection rate of approximately one half of the real runaway fraction. An age effect appears to be present, with objects of spectral subtype B1 and later having traveled for longer distances than runaways of earlier subtypes. We also tentatively propose that the fraction of runaways is lower among BA supergiants that among O stars, but further studies using future Gaia data releases are needed to confirm this. The frequency of fast rotators is high among runaway O stars, which indicates that a significant fraction of them (and possibly the majority) is produced in supernova explosions. ; J.M.A., A.S., and E.T.P. acknowledge support from the Spanish Government Ministerio de Economía, Industria y Competitividad (MINECO/FEDER) through grant No. AYA2016-75 931-C2-2-P. M.P.G. acknowledges support from the ESAC Trainee program. R.H.B. acknowledges support from the ESAC Faculty Council Visitor Program. S.S.-D., I.N., and E.T.P. acknowledge support from the Spanish Government Ministerio de Economía, Industria y Competitividad (MINECO/FEDER) through grant No. AYA2015-68 012-C2-1/2-P.

Context. The spectral classifications of the Galactic O-Star Spectroscopic Survey (GOSSS) and the astrometric and photometric data from Gaia have significantly improved our ability to measure distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with OB stars. In the near future, the situation will be further improved thanks to subsequent Gaia data releases and new photometric and spectroscopic surveys. Aims. We initiated a program to identify and determine the membership of Galactic stellar groups with OB stars and measure distances to them. Given the data currently available, we started 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 used GOSSS to select Galactic stellar groups with O2-O3.5 stars and the method described in paper 0 of this series, which combines Gaia DR2 G + GBP + GRP photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also included Collinder 419 and NGC 2264, the clusters cited in that paper, to generate our first list of 16 O-type Galactic stellar groups. Results. We derived distances, determined the membership, and analyzed the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to Villafranca O-016, including the fourteen groups with the earliest-O-type optically accessible stars known in the Milky Way. We compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) VLBI parallaxes and the worst is with kinematic distances. Our results indicate that very 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 Haffner 18 (Villafranca O-012 S). Our results are consistent with a difference of ≈20 μas in the Gaia DR2 parallax zero point between bright and faint stars. © ESO 2020. ; J.M.A. and A.S. acknowledge support from the Spanish Government Ministerio de Ciencia through grants AYA2016-75 931-C2-2-P and PGC2018-095 049-B-C22. R.H.B. acknowledges support from DIDULS Project 18 143 and the ESAC visitors program. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Additionally, this paper includes data obtained with the MPG/ESO 2.2m Telescope at the Observatorio de La Silla, Chile; the 2.5m du Pont Telescope at the Observatorio de Las Campanas, Chile; the 10m HobbyEberly Telescope at McDonald Observatory, Texas, USA; the 4.2m William Herschel Telescope and the 10.4m Gran Telescopio Canarias at the Observatorio del Roque de los Muchachos, La Palma, Spain; and the 2.2m Telescope at the Centro Astronomico Hispano Andaluz, Almeria, Spain. We thank the sta ff at those observatories for their support. This research has made extensive use of the SIMBAD and VizieR databases, operated at CDS, Strasbourg, France. ; Peer reviewed