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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

MUDEHaR is an on-going multi-epoch photometric survey with two narrow filters in H$\alpha$ and the calcium triplet window that uses the T80Cam wide-field imager at the JAST/T80 telescope at Spanish Javalambre astronomical observatory. It is obtaining 100 epochs/year per field for 20 fields in the Galactic disk, each of 2\,deg$^2$, for a total of 40\,deg$^2$. Focused on stellar clusters and HII regions including bright stars, its main objective is to detect tens of thousands OB stars that present emission variability in H$\alpha$ on days-months-years scale. The observed targets include magnetic massive stars, pulsating stars, and all kinds of variable stars. Among our driving scientific objectives of MUDEHaR observations is to identify potential magnetic candidates in massive stars. Only 10--20\,\% of OB stars display a measurable magnetic field, and its origin is still in debate. We outline here the multi-step process involved in identifying OB magnetic stars, highlighting the significance of MUDEHaR observations in this process., Comment: 11 pages, 5 figures. To appear in the edition of the Central European Astrophysical Bulletin dedicated to the proceedings of the Hvar Stellar Meeting 2023

There is increasing evidence that single-star evolutionary models are inadequate to reproduce all observational properties of massive stars. Binary interaction has emerged as a key factor in the evolution of a significant fraction of massive stars. In this study, we investigate the helium ($Y_{\mathrm He}$) and nitrogen ($\epsilon_{\mathrm N}$) surface abundances in a comprehensive sample of 180 Galactic O-type stars with projected rotational velocities $v\sin(i)\leq150{\mathrm km}\cdot{\mathrm s}^{-1}$. We found a subsample ($\sim20\%$ of the total, and $\sim80\%$ of the stars with $Y_{\mathrm He}\geq0.12$) with a $Y_{\mathrm He}$ and $\epsilon_{\mathrm N}$ combined pattern unexplainable by single-star evolution. We argue that the stars with anomalous surface abundance patterns are binary interaction products., Comment: Accepted for publication as Letter in A&A. 10 pages, 5 figures

Surveys in the Milky Way and Large Magellanic Cloud revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, which approaches the conditions of the Early Universe, remains sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign - an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the SMC - the lowest metallicity conditions in which multiplicity is probed to date (Z = 0.2 Zsun). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods P < 3 yr, (iii) dormant OB+BH binaries, and (iv) a legacy database of physical parameters of massive stars at low metallicity. The stars are observed with the LR02 setup of the giraffe instrument of the Very Large Telescope (3960-4570A, resolving power R=6200; typical signal-to-noise ratio S/N=70-100). This paper utilises the first 9 epochs obtained over a three-month time. We describe the survey and data reduction, perform a spectral classification of the stacked spectra, and construct a Hertzsprung-Russell diagram of the sample via spectral-type and photometric calibrations. The sample covers spectral types from O4 to F5, spanning the effective temperature and luminosity ranges 6.5

Observations have definitively strengthened the long-standing assertion that binaries are crucial in massive star evolution. While the percentage of spectroscopic binary systems among main-sequence O stars is well-studied, other phases of massive star evolution remain less explored. We aim to estimate the spectroscopic binary fraction in Galactic late O- and B-type supergiants (OB-Sgs) and set empirical thresholds in radial velocity (RV) to avoid misidentifying pulsating stars as single-line spectroscopic binaries. Using over 4500 high-resolution spectra of 56 Galactic OB-Sgs (plus 13 O dwarfs/subgiants and 5 early-B giants) from the IACOB project (2008-2020), we apply Gaussian fitting and centroid computation techniques to measure RV for each spectrum. Our findings reveal that intrinsic variability in OB-Sgs can result in peak-to-peak RV amplitudes (RVpp) of up to 20-25 km/s, notably in late-O and early-B Sgs, and decreases to typical values of RVpp in the range of 1-5 km/s for O dwarfs and 2-15 km/s for late B-Sgs. Considering these results and evaluating line-profile variability in each star, we find that 10$\pm$4% of OB-Sgs are clearly single-line spectroscopic binaries. In addition, we find that the percentage of double-line spectroscopic binaries in late O- and early B-Sgs is ~6%, much lower than the ~30% in O-type dwarfs and giants. This study, along with prior research on B-Sgs in the 30 Doradus region of the LMC, indicates that the spectroscopic binary percentage decreases by a factor of 4-5 from O stars to B-Sgs. Our study underscores the need for a thorough characterization of spectroscopic variability due to intrinsic sources to reliably determine the spectroscopic binary fraction among OB-Sgs and O-type stars in general, offering valuable insights into the impact of binaries on massive star evolution., Comment: This manuscript, submitted to A&A by mid 2020, encountered some discrepancies between the 1st author and the referee, along with some personal challenges during the COVID-19 pandemic, preventing its acceptance in a reasonable timescale. Believing it still valuable, I have decided to upload it to ArXiv as it was in 2021. A follow-up paper with a larger sample will be submitted soon

CONTEXT: The unparalleled characteristics of Gaia photometry make it an excellent choice to study stellar variability. AIMS: To measure the phot. dispersion in G+G_BP+G_RP of the 145 677 450 Gaia DR3 5-parameter sources with G <= 17 mag and G_BP-G_RP with -1.0 to 8.0 mag. To use that unbiased sample to analyze stellar variability in the Milky Way, LMC, and SMC. METHODS: We convert from magnitude uncertainties to the observed phot. dispersions, calculate the instrumental component as a function of apparent magnitude and color, and use it to transform the observed dispersions into the astrophysical ones. We give variability indices in the three bands for the whole sample. We use the subsample of Rimoldini et al. that includes light curves and variability types to calibrate our results and establish their limitations. RESULTS: We use information from the MW, LMC, and SMC CAMDs to discuss variability across the HRD. WDs and sdBs are more variable than MS or RC stars but their variability decreases for the former with age. The MS region in the Gaia CAMD has an s_G distribution peaks at low values (~1-2 mmag) and has a large tail dominated by EBs, RR Lyr stars, and YSOs. RC stars are characterized by little variability, with their s_G distribution peaking at 1 mmag or less. The stars in the PMS region are highly variable, with a power law distribution in s_G with slope 2.75 and a cutoff for values lower than 7 mmag. The luminous red stars region of the Gaia CAMD has the highest variability, with its extreme dominated by AGB stars and with a power law in s_G with a slope of ~2.2 that extends from there to a cutoff of 7 mmag. We show that our method can be used to search for LMC Cepheids. We analyze four stellar clusters with O stars and detect a strong difference in s_G between stars that are already in the MS and those that are still in the PMS. [ABRIDGED BUT NOT TOO FAR], Comment: Submitted to A&A. Comments welcome. Second version improved with: [a] Appendix figures included. [b] Changed from 3 to 5 color bins to reduce residual instrumental effects. [c] Figure changes caused by [b]. [d] Minor content additions. [e] Some typos corrected

The empirical distribution of projected rotational velocities (vsini) in massive O-type stars is characterized by a dominant slow velocity component and a tail of fast rotators. Binary interaction has been proposed to play a dominant role in the formation of this tail. We perform a complete and homogeneous search for empirical signatures of binarity in a sample of 54 fast-rotating stars with the aim of evaluating this hypothesis. This working sample has been extracted from a larger sample of 415 Galactic O-type stars which covers the full range of vsini values. We use new and archival multi-epoch spectra in order to detect spectroscopic binary systems. We complement this information with Gaia proper motions and TESS photometric data to aid in the identification of runaway stars and eclipsing binaries, respectively. The identified fraction of single-lined spectroscopic binary (SB1) systems and apparently single stars among the fast-rotating sample is $\sim$18% and $\sim$70%, respectively. When comparing these percentages with those corresponding to the slow-rotating sample we find that our sample of fast rotators is characterized by a slightly larger percentage of SB1 systems ($\sim$18% vs. $\sim$13%) and a considerably smaller fraction of clearly detected SB2 systems (8% vs. 33%). Overall, there seems to be a clear deficit of spectroscopic binaries (SB1+SB2) among fast-rotating O-type stars ($\sim$26% vs. $\sim$46%). On the contrary, the fraction of runaway stars is significantly higher in the fast-rotating domain ($\sim$33-50%) than among those stars with vsini < 200 km/s. Lastly, almost 65% of the apparently single fast-rotating stars are runaways. Our empirical results seem to be in good agreement with the idea that the tail of fast-rotating O-type stars (with vsini > 200 km/s) is mostly populated by post-interaction binary products., Comment: 33 pages, 16 figures, accepted for publication in "Astronomy and Astrophysics"

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., Comment: 24 pages, 19 figures, accepted for publication in Astronomy & Astrophysics

The Gaia-ESO Survey (GES) is a large public spectroscopic survey that has collected, over a period of 6 years, spectra of ~ 10^5 stars. This survey provides not only the reduced spectra, but also the stellar parameters and abundances resulting from the analysis of the spectra. 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 cut-off 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. The procedure used is similar to that of other working groups in GES. A number of groups (called `Nodes') each independently analyse the spectra, using their state-of-the-art techniques and codes. Specific for the analysis in WG13 is the large temperature range that is covered (Teff = 7000 - 50,000 K), requiring the use of different analysis codes. Most Nodes can therefore only handle part of the data. Quality checks are applied to the results of these Nodes by comparing them to benchmark stars, and by comparing them one to another. For each star the Node values are then homogenised into a single result: the recommended parameters and abundances. 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. Elements studied are He, C, N, O, Ne, Mg, Al, Si and Sc. Abundances for at least one of those elements were determined for 292 stars. The hot-star data analysed here, as well as the Gaia-ESO Survey data in general, will be of considerable use in future studies of stellar evolution and open clusters., Comment: 26 pages, 14 figures, accepted for publication in Astronomy & Astrophysics; language-edited version; two appendices merged

The GALANTE optical photometric survey is observing the northern Galactic plane and some adjacent regions using seven narrow- and intermediate-filters, covering a total of 1618 square degrees. The survey has been designed with multiple exposure times and at least two different air masses per field to maximize its photometric dynamic range, comparable to that of Gaia, and ensure the accuracy of its photometric calibration. The goal is to reach at least 1% accuracy and precision in the seven bands for all stars brighter than AB magnitude 17 while detecting fainter stars with lower values of the signal-to-noise ratio.The main purposes of GALANTE are the identification and study of extinguished O+B+WR stars, the derivation of their extinction characteristics, and the cataloguing of F and G stars in the solar neighbourhood. Its data will be also used for a variety of other stellar studies and to generate a high-resolution continuum-free map of the H{\alpha} emission in the Galactic plane. We describe the techniques and the pipeline that are being used to process the data, including the basis of an innovative calibration system based on Gaia DR2 and 2MASS photometry., Comment: 18 pages, accepted for publication in MNRAS

[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., Comment: Table 10 and Appendix C are available at the CDS

Spectroscopic studies of Galactic O and B stars show that many stars with masses above 8 M$_{\odot}$ are observed in the HR diagram just beyond the Main-Sequence (MS) band predicted by stellar models computed with a moderate overshooting. This may be an indication that the convective core sizes in stars in the upper part of the HR diagram are larger than predicted by these models. Combining stellar evolution models and spectroscopic parameters derived for a large sample of Galactic O and B stars, including brand new information about their projected rotational velocities, we reexamine the question of the convective core size in MS massive stars. We confirm that for stars more massive than about 8 M$_{\odot}$, the convective core size at the end of the MS phase increases more rapidly with the mass than in models computed with a constant step overshoot chosen to reproduce the main sequence width in the low mass range (around 2 M$_{\odot}$). This conclusion is valid for both the cases of non-rotating models and rotating models either with a moderate or a strong angular momentum transport. The increase of the convective core mass with the mass obtained from the TAMS position is, however, larger than the one deduced from the surface velocity drop for masses above about 15 M$_{\odot}$. Although observations available at the moment cannot decide what is the best choice between the core sizes given by the TAMS and the velocity drop, we discuss different methods to get out of this dilemma. At the moment, comparisons with eclipsing binaries seem to favor the solution given by the velocity drop. While we confirm the need for larger convective cores at higher masses, we find tensions in-between different methods for stars more massive than 15 M$_{\odot}$. The use of single-aged stellar populations (non-interacting binaries or stellar clusters) would be a great asset to resolve this tension., Comment: 13 pages, 8 figures

CONTEXT. Many massive stars have nearby companions whose presence hamper their characterization through spectroscopy. AIMS. We want to continue obtaining spatially resolved spectroscopy of close massive visual binaries to derive their spectral types. METHODS. We have used lucky spectroscopy to obtain many 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 are 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 to [a] spatially disentangle for the first time two O stars (FN CMa B and 6 Cas B) with brighter BA supergiant companions; [b] determine that two B stars (alpha Sco B and HD 164492 B) with close and more massive companions are fast rotators; [c] extend the technique to cases with extreme magnitude differences, shorter separations, and fainter primary magnitudes down to B=11; [d] spatially disentangle the spectra of stars with companions as diverse as an A supergiant (6 Cas A), a WR star (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 51756 B and BD +60 544) and a new member of the rare OC category (HD 8768 A); and [f] identify and classify which of the components of four visual binaries is a double-lined spectroscopic binary and for another seven systems detect signs of spectroscopic binarity using high-spectral-resolution spectroscopy. We also present a determination of the limits of the technique. [ABRIDGED], Comment: Accepted for publication in A&A

The relevance of M dwarfs in the search for potentially habitable Earth-sized planets has grown significantly in the last years. In our on-going effort to comprehensively and accurately characterise confirmed and potential planet-hosting M dwarfs, in particular for the CARMENES survey, we have carried out a comprehensive multi-band photometric analysis involving spectral energy distributions, luminosities, absolute magnitudes, colours, and spectral types, from which we have derived basic astrophysical parameters. We have carefully compiled photometry in 20 passbands from the ultraviolet to the mid-infrared, and combined it with the latest parallactic distances and close-multiplicity information, mostly from Gaia DR2, of a sample of 2479 K5V to L8 stars and ultracool dwarfs, including 2210 nearby, bright M dwarfs. For this, we made extensive use of Virtual Observatory tools. We have homogeneously computed accurate bolometric luminosities and effective temperatures of 1843 single stars, derived their radii and masses, studied the impact of metallicity, and compared our results with the literature. The over 40000 individually inspected magnitudes, together with the basic data and derived parameters of the stars, individual and averaged by spectral type, have been made public to the astronomical community. In addition, we have reported 40 new close multiple systems and candidates rho < 3.3 arcsec and 36 overluminous stars that are assigned to young Galactic populations. In the new era of exoplanet searches around M dwarfs via transit (e.g. TESS, PLATO) and radial velocity (e.g. CARMENES, NIRPS+HARPS), this work is of fundamental importance for stellar and therefore planetary parameter determination., Comment: 33 pages, 62 Postscript figures, uses aalongtable.sty

Lack of high-precision long-term continuous photometric data for large samples of stars has prevented the large-scale exploration of pulsational variability in the OB star regime. As a result, the candidates for in-depth asteroseismic modelling remained limited to a few tens of dwarfs. The TESS nominal space mission has surveyed the southern sky, yielding continuous data of at least 27 d for hundreds of OB stars. We aim to couple TESS data in the southern sky with spectroscopy to study the variability over mass and evolution. We focus mainly on the presence of coherent pulsation modes that may or may not be present in the theoretical instability domains and unravel all frequency behaviour in the amplitude spectra of the TESS data. We compose a sample of 98 OB-type stars observed by TESS in Sectors 1-13 and with available high-resolution spectroscopy gathered by the IACOB and OWN surveys. We present the short-cadence 2-min light curves of dozens of OB-type stars, that have one or more spectra in the IACOB or OWN database. Based on these light curves and their Lomb-Scargle periodograms we perform variability classification and frequency analysis, and place the stars in the spectroscopic Hertzsprung-Russell diagram to interpret the variability in an evolutionary context. We deduce diverse origins of the variability found in all of the 98 OB stars in the TESS data. Among these we find several new variable stars, including three hybrid pulsators, three eclipsing binaries, high frequency modes in a Be star, and potential heat-driven pulsations in two Oe stars. We identify stars for which future asteroseismic modelling is possible, provided mode identification is achieved. By comparing the position of the variables to theoretical instability strips we discuss the current shortcomings in non-adiabatic pulsation theory, and the distribution of pulsators in the upper Hertzsprung-Russell diagram., Comment: Accepted for publication in A&A. 18(+47) pages, 15(+100) figures, 3(+2) tables. Language edited and typos removed. Fig. 3, 14, 15 corrected for small plotting error (results unchanged)

The apparent lack of massive O-type stars near the zero-age main sequence (at ages < 2 Myr) is a topic widely discussed. Different explanations for this elusive detection have been proposed, but no firm conclusions have been reached yet. We reassess this empirical result benefiting from the high-quality spectroscopic observations of >400 Galactic O-type stars gathered by the IACOB and OWN surveys. We used temperatures and gravities from a iacob-gbat/fastwind spectroscopic analysis to locate our sample in the Kiel and spectroscopic HR diagrams. We evaluated the completeness of our sample of stars, observational biases using information from the Galactic O star catalog (GOSC), systematics of our methodology, and compare with other recent studies using smaller samples of Galactic O-type stars. We base our discussion on the spectroscopic HR diagram to avoid the use of uncertain distances. We performed a detailed study of the young cluster Trumpler-14 as an example of how Gaia cluster distances can help to construct the associated classical HR diagram. The apparent lack of massive O-type stars near the ZAMS with masses between 30 and 70 Msol persist even when spectroscopic results from a large, non-biased sample of stars are used. We do not find correlation between the dearth of stars and observational biases, limitations of our methodology, or the use of spectroscopic HR diagram instead of the classical one. Investigating the efficiency of mass accretion during the formation process we conclude that an adjustment of the accretion rate towards lower values could reconcile the hotter boundary of detected O-type stars and the theoretical birthline. Last, we discuss that the presence of a small sample of O2-O3.5 stars found closer to the ZAMS might be explained taking into account non-standard star evolution (e.g. binary interaction, mergers, or homogeneous evolution)., Comment: 20 pages, 15 figures, accepted for publication in Astronomy & Astrophysics

Statistical analyses from exoplanet surveys around low-mass stars indicate that super-Earth and Neptune-mass planets are more frequent than gas giants around such stars, in agreement with core accretion theory of planet formation. Using precise radial velocities derived from visual and near-infrared spectra, we report the discovery of a giant planet with a minimum mass of 0.46 Jupiter masses in an eccentric 204-day orbit around the very low-mass star GJ 3512. Dynamical models show that the high eccentricity of the orbit is most likely explained from planet-planet interactions. The reported planetary system challenges current formation theories and puts stringent constraints on the accretion and migration rates of planet formation and evolution models, indicating that disc instability may be more efficient in forming planets than previously thought., Comment: Manuscript author version. 41 pages, 11 figures

Boyajian's star is an apparently normal main sequence F-type star with a very unusual light curve. The dipping activity of the star, discovered during the Kepler mission, presents deep, asymmetric, and aperiodic events. Here we present high resolution spectroscopic follow-up during some dimming events recorded post-Kepler observations, from ground-based telescopes. We analise data from the HERMES, HARPS-N and FIES spectrographs to characterise the stellar atmosphere and to put some constraints on the hypotheses that have appeared in the literature concerning the occulting elements. The star's magnetism, if existing, is not extreme. The spots on the surface, if present, would occupy 0.02% of the area, at most. The chromosphere, irrespective of the epoch of observation, is hotter than the values expected from radiative equilibrium, meaning that the star has some degree of activity. We find no clear evidence of the interstellar medium nor exocoments being responsible for the dimmings of the light curve. However, we detect at 1-2 sigma level, a decrease of the radial velocity of the star during the first dip recorded after the \emph{\emph{Kepler}} observations. We claim the presence of an optically thick object with likely inclined and high impact parameter orbits that produces the observed Rossiter-McLaughlin effect., Comment: submitted to MNRAS

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process., Comment: 19 pages, 8 figures, accepted for publication in ApJL

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. As a first step in the study of the full sample of (more than 350) O stars surveyed by the IACOB/OWN projects, 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. We use semi-automatized tools to determine the set of spectroscopic parameters that can be obtained from the optical spectrum of O-type stars. We also benefit from the multi-epoch character of the surveys to perform a spectroscopic variability study of the sample, accounting for spectroscopic binarity and variability of the main wind diagnostic lines. We provide a general overview of the stellar and wind parameters of this reference sample, and updated recipes for the SpT\,--\,Teff/log g calibrations for Galactic O-type stars. We evaluate our semi-automatized analysis strategy with $\sim$40 stars from the literature, and find a good agreement. The agreement between the synthetic spectra associated with fastwind best fitting models and the observed spectra is good for most targets, but 46 stars 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 components. Last, our variability study has led to the detection of 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., Comment: 20 pages, 18 figures, accepted for publication in Astronomy & Astrophysics

The VLT-FLAMES Tarantula Survey has observed hundreds of O-type stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). We study the properties of 105 apparently single O-type dwarfs. To determine stellar and wind parameters, we used the IACOB-GBAT package, an automatic procedure based on a large grid of atmospheric models calculated with the FASTWIND code. In addition to classical techniques, we applied the Bayesian BONNSAI tool to estimate evolutionary masses. We provide a new calibration of effective temperature vs. spectral type for O-type dwarfs in the LMC, based on our homogeneous analysis of the largest sample of such objects to date and including all spectral subtypes. Good agreement with previous results is found, although the sampling at the earliest subtypes could be improved. Rotation rates and helium abundances are studied in an evolutionary context. We find that most of the rapid rotators (vsini higher than 300 km/s ) in our sample have masses below 25 MSun and intermediate rotation-corrected gravities (log gc between 3.9 and 4.1). Such rapid rotators are scarce at higher gravities (i.e. younger ages) and absent at lower gravities (larger ages). This is not expected from theoretical evolutionary models, and does not appear to be due to a selection bias in our sample. We compare the estimated evolutionary and spectroscopic masses, finding a trend that the former is higher for masses below 20 MSun. This can be explained as a consequence of limiting our sample to the O-type stars, and we see no compelling evidence for a systematic mass discrepancy. For most of the stars in the sample we were unable to estimate the wind-strength parameter (hence mass-loss rates) reliably, particularly for objects with luminosity lower than logL/LSun about 5.1. Ultraviolet spectroscopy is needed to undertake a detailed investigation of the wind properties of these dwarfs., Comment: 23 pages, 16 figures. Accepted for publication in A&A

We present first results from the quantitative spectroscopic analysis of 266 Galactic O-type stars targeted by the IACOB and OWN surveys (implying the largest sample of stars of this type analyzed homogeneously). We also evaluate what is the present situation regarding available information about distances, as provided by the Hipparcos and Gaia missions., Comment: To appear in Highlights on Spanish Astrophysics IX, Proceedings of the XII Scientific Meeting of the Spanish Astronomical Society held on July 18-22, 2016, in Bilbao, Spain

The IACOB project is an ambitious long-term project which is contributing to step forward in our knowledge about the physical properties and evolution of Galactic massive stars. The project aims at building a large database of high-resolution, multi-epoch, spectra of Galactic OB stars, and the scientific exploitation of the database using state-of-the-art models and techniques. In this proceeding, we summarize the latest updates of the IACOB spectroscopic database and highlight some of the first scientific results from the IACOB project; we also announce the first data release and the first public version of the iacob-broad tool for the line-broadening characterization of OB-type spectra., Comment: To appear in Highlights of Spanish Astrophysics VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical Society held on September 8-12, 2014, in Teruel, Spain