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We present results from a recent study of the spin rate properties of a sample of more than 400 Galactic O-type stars surveyed by the IACOB and OWN projects. We combine vsini, Teff, and logg estimates with information about the spectroscopic binarity status for 285 of the stars in the sample, and 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 state-of-the-art 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 M⊙. [ABSTRACT FROM AUTHOR]

In this contribution we present the results from a1 homogeneous quantitative spectroscopic analysis of ∼400 Galactic O-type stars targeted by the IACOB and OWN surveys. The ultimate objective is to perform a modern reassessment of one of the long-standing problems in the field of massive stars: the elusive detection of mid O-type stars close to the "canonical" theoretical ZAMS. We first provide statistically significant evidence of the existence of a clear lack of stars in our sample populating the region of the spectroscopic HR diagram approximately delimited by the theoretical ZAMS, the ∼ 40 and ∼ 70 M⊙ single evolutionary tracks and the 2 Myr isochrone. We then evaluate if this empirical result could be a result of possible limitations of our analysis strategy and/or the existence of potential observational biases affecting the compiled sample. Once both explanations are investigated, we evaluate the possibility that a modification of the efficiency of mass accretion during the star formation process could lead to a new (corrected) theoretical ZAMS in better accordance with our empirical results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Context. The unparalleled characteristics of Gaia photometry in terms of calibration, stability, time span, dynamic range, full-sky coverage, and complementary information make it an excellent choice to study stellar variability. Aims. We aim to measure the photometric dispersion in the G, GBP, and GRP bands of the 145 677 450 third Gaia data release (DR3) five-parameter sources with G ≤ 17 mag and GBP – GRP between −1.0 and 8.0 mag. We will use that unbiased sample to analyze stellar variability in the Milky Way (MW), Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC). Methods. For each band we convert from magnitude uncertainties to observed photometric 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: sG, SGBP, and SGRP. We give variability indices in the three bands for the whole sample indicating whether the objects are non-variable, marginally variable, or clearly so. We use the subsample established by Rimoldini and collaborators with light curves and variability types to calibrate our results and establish their limitations. Results. The position of an object in the dispersion-dispersion planes can be used to constrain its variability type, a direct application of these results. We use information from the MW, LMC, and SMC color-absolute magnitude diagrams (CAMDs) to discuss variability across the Hertzsprung-Russell diagram. White dwarfs and B-type subdwarfs are more variable than main sequence (MS) or red clump (RC) stars, with a flat distribution in sG up to 10 mmag and with variability decreasing for the former with age. The MS region in the Gaia CAMD includes a mixture of populations from the MS itself and from other evolutionary phases. Its sG distribution peaks at low values (~1–2 mmag) but it has a large tail dominated by eclipsing binaries, RR Lyrae stars, and young stellar objects. RC stars are characterized by little variability, with their sG distribution peaking at 1 mmag or less. The stars in the pre-main-sequence (PMS) region are highly variable, with a power law distribution in sG 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 sG with slope ~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 (Villafranca O-016, O-021, O-024, and O-026) and detect a strong difference in sG between stars that are already in the MS and those that are still in the PMS. [ABSTRACT FROM AUTHOR]

Context. The empirical distribution of projected rotational velocities (v sin i) in massive O-type stars is characterised by a dominant slow velocity component and a tail of fast rotators. It has been proposed that binary interaction plays a dominant role in the formation of this tail. Aims. 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 that covers the full range of v sin i values. Methods. We used new and archival multi-epoch spectra in order to detect spectroscopic binary systems. We complemented this information with Gaia proper motions and TESS photometric data to aid in the identification of runaway stars and eclipsing binaries, respectively. We also benefitted from additional published information to provide a more complete overview of the empirical properties of our working sample of fast-rotating O-type stars. Results. The identified fraction of single-lined spectroscopic binary (SB1) systems and apparently single stars among the fast-rotating sample is ~18% and ~70%, respectively. The remaining 12% correspond to four secure double-line spectroscopic binaries (SB2) with at least one of the components having a v sin i > 200 km s1 (~8%), along with a small sample of 2 stars (~4%) for which the SB2 classification is doubtful: these could actually be single stars with a remarkable line-profile variability. When comparing these percentages with those corresponding to the slow-rotating sample, we find that our sample of fast rotators is characterised by a slightly larger percentage of SB1 systems (~18% vs. ~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 (~26% vs. ~46%). On the contrary, the fraction of runaway stars is significantly higher in the fast-rotating domain (~33-50%) than among those stars with v sin i < 200 km s1. Lastly, almost 65% of the apparently single fast-rotating stars are runaways. As a by-product, we discovered a new over-contact SB2 system (HD 165921) and two fast-rotating SB1 systems (HD 46485 and HD152200) Also, we propose HD94024 and HD12323 (both SB1 systems with a v sin i < 200 km s1) as candidates for hosting a quiescent stellar-mass black hole. Conclusions. Our empirical results seem to be in good agreement with the assumption that the tail of fast-rotating O-type stars (with v sin i > 200 km s1) is mostly populated by post-interaction binary products. In particular, we find that the final statistics of identified spectroscopic binaries and apparent single stars are in good agreement with newly computed predictions obtained with the binary population synthesis code BPASS and earlier estimations obtained in previous studies. [ABSTRACT FROM AUTHOR]

We present results from a recent study of the spin rate properties of a sample of more than 400 Galactic O-type stars surveyed by the IACOB and OWN projects. We combine vsini, Teff, and logg estimates with information about the spectroscopic binarity status for 285 of the stars in the sample, and 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 state-of-the-art 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 M⊙. [ABSTRACT FROM AUTHOR]

Rotation is one of the important parameters affecting the evolution and final fate of massive stars but the origin of fast rotators remains unclear (imprint of the star formation process, result of binary interactions). In this work, we aim at investigating the binary status, photometric variability, and runaway status of a statistically meaningful sample of Galactic fast-rotating O stars. We perform a comprehensive multi-epoch analysis of new high-quality spectroscopic observations gathered by the IACOB and OWN surveys. Notably, we find that the total percentage of spectroscopic binaries in the investigated sample range between 25 and 40%, in agreement with previous finding for the case of O-type stars with lower projected rotational velocities. On the contrary, the fraction of runaway stars among fast rotators (∼35–50%) is significantly higher than in the case of slow rotators (∼20–30%). By combining all these observational results we will evaluate each scenario about the origin of fast rotators. [ABSTRACT FROM AUTHOR]

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 deg2. 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 per cent 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 α 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. [ABSTRACT FROM AUTHOR]

In this contribution we present the results from a1 homogeneous quantitative spectroscopic analysis of ∼400 Galactic O-type stars targeted by the IACOB and OWN surveys. The ultimate objective is to perform a modern reassessment of one of the long-standing problems in the field of massive stars: the elusive detection of mid O-type stars close to the "canonical" theoretical ZAMS. We first provide statistically significant evidence of the existence of a clear lack of stars in our sample populating the region of the spectroscopic HR diagram approximately delimited by the theoretical ZAMS, the ∼ 40 and ∼ 70 M⊙ single evolutionary tracks and the 2 Myr isochrone. We then evaluate if this empirical result could be a result of possible limitations of our analysis strategy and/or the existence of potential observational biases affecting the compiled sample. Once both explanations are investigated, we evaluate the possibility that a modification of the efficiency of mass accretion during the star formation process could lead to a new (corrected) theoretical ZAMS in better accordance with our empirical results. [ABSTRACT FROM AUTHOR]

Context. The relevance of M dwarfs in the search for potentially habitable Earth-sized planets has grown significantly in the last years. Aims. 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. Methods. 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 K5 V to L8 stars and ultracool dwarfs, including 2210 nearby, bright M dwarfs. For this, we made extensive use of Virtual Observatory tools. Results. 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 40 000 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 (ρ <  3.3 arcsec) and 36 overluminous stars that are assigned to young Galactic populations. Conclusions. 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. [ABSTRACT FROM AUTHOR]

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 analyse data from the HERMES, HARPS-N, and FIES spectrographs to characterize 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 per cent 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 or exocoments being responsible for the dimmings of the light curve. However, we detect at 1–2σ level, a decrease of the radial velocity of the star during the first dip recorded after the 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. [ABSTRACT FROM AUTHOR]

Context. Rotational mixing is known to significantly affect the evolution of massive stars; however, we still lack a consensus regarding the various possible modeling approaches and mixing recipes describing this process. The empirical investigation of surface abundances of carbon, nitrogen, and oxygen (CNO) in large samples of O- and B-type stars will be essential for providing meaningful observational constraints on the different available stellar evolution models. Aims. Setting up and testing adequate tools to perform CNO surface abundance determinations for large samples of O-type stars, by means of the fast performance, NLTE, unified model atmosphere code FASTWIND. Methods. We have developed a set of semi-automatic tools for measuring and analyzing the observed equivalent widths of strategic optical C, N, and O lines from different ions. Our analysis strategy is based on a χ2 minimization of weighted differences between observed and synthetic equivalent widths, the latter computed from tailored model grids. We have paid special attention to the (significant) errors introduced by typical uncertainties in stellar parameters. In this pilot study, we describe these tools, and test their performance and reliability using a set of high quality spectra of a sample of 18 presumably single Galactic O-type stars with low projected rotational velocities (v sin i≲100 km s−1), and previously determined stellar parameters. In particular, we have compared the outcome of our analysis with results from existing studies and theoretical stellar evolution models. Results. Most of our results for carbon and nitrogen agree, within the errors, with both theoretical expectations and literature values. While many cooler dwarfs display C and N abundances close to solar, some of the early- and mid-O dwarfs – and most supergiants – show significant enrichment in N and depletion in C. Our results for oxygen in late-O dwarfs are, however, unexpectedly low, possibly indicating deficiencies in the adopted oxygen model atom. For all other objects, no systematic problems in their oxygen content have been identified. Specific stars in our sample show peculiarities in their abundances, and we suggest hypotheses regarding their origin. Conclusions. Our method is (almost) ready to be applied to large samples of late and mid O-type stars – although the oxygen model atom needs to be improved and carefully tested first. For early O-type stars (O4 and hotter), a simultaneous UV analysis seems to be inevitable, due to the scarcity and weakness of optical C and O lines. This will necessarily imply a more complex modeling, additionally accounting for the effects of X-rays from wind-embedded shocks and wind inhomogeneities. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Context: The VLT-FLAMES Tarantula Survey has observed hundreds of O-type stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). Aims: We study the properties of a statistically significant sample of O-type dwarfs in the same star-forming region and test the latest atmospheric and evolutionary models of the early main-sequence phase of massive stars. Methods: We performed quantitative spectroscopic analysis 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 that are calculated with the fastwind code. This package was developed for the analysis of optical spectra of O-type stars. In addition to classical techniques, we applied the Bayesian bonnsai tool to estimate evolutionary masses. Results: 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 (v sin i > 300 km s-1) in our sample have masses below ~25 M⊙ and intermediate rotation-corrected gravities (3.9 < log gc < 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 M⊙. 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 lower luminosity (log L/L⊙ ≲ 5.1). Only with ultraviolet spectroscopy will we be able to undertake a detailed investigation of the wind properties of these dwarfs. [ABSTRACT FROM AUTHOR]

Rotation is one of the important parameters affecting the evolution and final fate of massive stars but the origin of fast rotators remains unclear (imprint of the star formation process, result of binary interactions). In this work, we aim at investigating the binary status, photometric variability, and runaway status of a statistically meaningful sample of Galactic fast-rotating O stars. We perform a comprehensive multi-epoch analysis of new high-quality spectroscopic observations gathered by the IACOB and OWN surveys. Notably, we find that the total percentage of spectroscopic binaries in the investigated sample range between 25 and 40%, in agreement with previous finding for the case of O-type stars with lower projected rotational velocities. On the contrary, the fraction of runaway stars among fast rotators (∼35–50%) is significantly higher than in the case of slow rotators (∼20–30%). By combining all these observational results we will evaluate each scenario about the origin of fast rotators. [ABSTRACT FROM AUTHOR]

Thioredoxin reductases control the redox state of thioredoxins (Trxs)-ubiquitous proteins that regulate a spectrum of enzymes by dithiol-disulfide exchange reactions. In most organisms, Trx is reduced by NADPH via a thioredoxin reductase flavoenzyme (NTR), but in oxygenic photosynthetic organisms, this function can also be performed by an iron-sulfur ferredoxin (Fdx)-dependent thioredoxin reductase (FTR) that links light to metabolic regulation. We have recently found that some cyanobacteria, such as the thylakoid-less Gloeobacter and the ocean-dwelling green oxyphotobacterium Prochlorococcus, lack NTR and FTR but contain a thioredoxin reductase flavoenzyme (formerly tentatively called deeply-rooted thioredoxin reductase or DTR), whose electron donor remained undefined. Here, we demonstrate that Fdx functions in this capacity and report the crystallographic structure of the transient complex between the plant-type Fdx1 and the thioredoxin reductase flavoenzyme from Gloeobacter violaceus. Thereby, our data demonstrate that this cyanobacterial enzyme belongs to the Fdx flavin-thioredoxin reductase (FFTR) family, originally described in the anaerobic bacterium Clostridium pasteurianum. Accordingly, the enzyme hitherto termed DTR is renamed FFTR. Our experiments further show that the redox-sensitive peptide CP12 is modulated in vitro by the FFTR/Trx system, demonstrating that FFTR functionally substitutes for FTR in light-linked enzyme regulation in Gloeobacter. Altogether, we demonstrate the FFTR is spread within the cyanobacteria phylum and propose that, by substituting for FTR, it connects the reduction of target proteins to photosynthesis. Besides, the results indicate that FFTR acquisition constitutes a mechanism of evolutionary adaptation in marine phytoplankton such as Prochlorococcus that live in low-iron environments., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

The new cyclic peptide antibiotic, radamycin (1) and the known thiopeptide methylsulfomycin I (2) have been isolated from the fermentation broth of a Streptomyces sp. RSP9. The structure of radamycin was elucidated by NMR, LC-MS and FAB-MS and was established as a thiopeptide with oxazole and thiazole moieties, and several unusual amino acids.

The newly isolated strain Streptomyces sp. RSP9 produces two thiopeptides; one of them is methylsulfomycin I, which shows potent antibiotic activity against several gram-positive bacteria such as Micrococcus luteus and Staphylococcus aureus. The other is a new thiopeptide named radamycin. In the present work, this compound was purified and tested against several microorganisms and no antibiotic activity was detected in the assays. However, it does have a very strong capacity as an inducer of the tipA promoter, and indeed is the first reported molecule with tipA promoter induction capacity without detectable antibiotic activity. Induction of the tipA promoter also occurs with methylsulfomycin I.

Mitral valve prolapse was found in one of 133 patients with hypertension (0.75 percent) studied by two-dimensional echocardiography. This rarity may be related to the presence of hypertrophied papillary muscles that probably pull the chordae tendinae and mitral valve leaflets away from the left atrium in systole, thus preventing their eversion and prolapse.