Low metallicity (Z) massive stars are among the main feedback agents in the early Universe and in present-day blue dwarf galaxies. The nearby star-forming SMC galaxy offers conditions which resemble those at redshift z∼2 i.e. where modern galaxies formed and star formation peaked. Here we present the recent results about the nature of the eclipsing O-type binary in the SMC, AzV 476, to gain insights on the properties of massive stars and binaries at earlier cosmic epochs. We find that the primary has surprisingly low mass while being much brighter and hotter than the secondary. To place the measured stellar properties in the evolutionary context we modeled the system and confirm that AzV 476 is a post-interaction binary with the primary already being core helium (He) burning, while still having a hydrogen-rich (H-rich) envelope. These results constrain massive binary evolutionary scenarios and guide the searches of stripped stars in low-Z environments.

We have studied the validity of the historical Cygnus OB associations and have found that many do not show the kinematic coherence expected for true OB associations. We have revisited these groups by photometrically identifying thousands of OB stars across the region with an SED fitting process which combines photometry, astrometry, spectral and evolutionary models. We applied a flexible clustering method and identified seven kinematically-coherent new OB associations. We observe a distinct correlation between position and velocity for two sets of these associations that suggests an expansion pattern. Tracing the motion of the stars back in the past we find that the sets were at their closest around 7.9 and 8.5 Myr ago. We discuss whether this expansion is a natural by-product of the commonly observed size - velocity dispersion relation of molecular clouds, or requires feedback to initiate the dispersal.

During the last years we have carried out different studies in the Cygnus OB2 association based on new spectroscopic data and benefiting from the unprecedented Gaia astrometry. They include membership, chemical and structure studies, that allowed us to discern for the first time ever between two stellar groups separated by several hundred parsecs within the association and find at least two star-forming bursts at ∼3 and ∼5 Myr. Using these studies as a template and combining upcoming spectroscopic WEAVE data and the expected accuracy that Gaia will reach in the Cygnus-X area (DR3 and forthcoming releases), we will be able to perform the deepest multi-dimensional study ever done before in a massive star-forming complex. The results of this project will lead to an important improvement of our knowledge of star formation and evolution of star-forming regions and clusters, including our understanding of the dynamics and kinematics of OB associations and stellar groups.

Over the last two decades there have been considerable advances in modelling the spectra of massive stars and supernovae (SNe). Despite this progress, there are still numerous uncertainties that affect the accuracy of models. For massive stars, convection, instabilities, clumping, and our inability to model stellar winds self-consistently likely introduce systematic errors into our analyses. For SNe, and particularly for core-collapse SNe, departures from spherical symmetry strongly affect observed spectra and need to be taken into account. There are also issues with clumping, and mixing processes (both in the progenitor and the SN explosion) that need to be resolved. For both massive stars and SNe, the accuracy and availability of atomic data continues to be an ongoing issue influencing analyses.

Adequate stellar atmosphere models are prerequisite to derive robust stellar parameters from spectroscopic analyses. I will briefly review recent results obtained with the Potdam Wolf-Rayet (PoWR) model atmosphere code, which is applicable to all types of hot stars. Using multi-wavelength observations including the UV, we analyzed large samples of massive stars at various metallicities, gaining important insights on their cosmic role and the feedback to their environment.

A recent extension of PoWR allows to compose the model atmosphere from two zones. A rapidly rotating star, e.g., might possess a cooler equatorial region with a slow wind, and two polar cones with higher photospheric temperature and fast wind. For two examples of rapidly rotating O-type stars, we demonstrate that such model can reproduce wind-line profiles which otherwise would stay inconsistent. Fast rotation, which prevails in particular at low metallicities, thus might bias empirically derived parameters, having implications for feedback as well as for angular-momentum losses of SN and GRB progenitors.

Upcoming large-scale spectroscopic surveys such as WEAVE and 4MOST will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Studies on massive stars are usually based on samples of a few hundred objects which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit.

The novel spectroscopic analysis pipeline takes advantage of the statistics that large samples provide, and determines the model error to account for imperfections in stellar atmosphere codes due to simplified, wrong or missing physics. Considering observational plus model uncertainties improve spectroscopic fits. The pipeline utilises the entire spectrum rather than selected diagnostic lines allowing a wider range of temperature from B to early O stars to be analysed. A small fraction of stars like peculiar, contaminated or spectroscopic binaries require visual inspection, which are identified through their larger uncertainties.

We present the results obtained using spectroscopic data taken with the intermediate-resolution Multi Unit Spectroscopic Explorer (MUSE) of B and A-type supergiants and bright giants in the Sculptor Group galaxy NGC 300. For our analysis, a hybrid local thermodynamic equilibrium (LTE) line-blanketing+non-LTE method was used to improve the previously published results for the same data. In addition, we present some further applications of this work, which includes extending the flux-weighted gravity luminosity relationship (FGLR), a distance determination method for supergiants. This pioneering work opens up a new window to explore this relation, and also demonstrates the enormous potential of integral field spectroscopy (IFS) for extragalactic quantitative stellar studies.

Whether it be due to rapid rotation or binary interactions, deviations from spherical symmetry are common in massive stars. These deviations from spherical symmetry are known to cause non-uniform distributions of various parameters across the surface including temperature, which can drive internal mixing processes within the envelopes of these massive stars. Despite how common these 3D distortions are, they are often neglected in spectroscopic analyses. We present a new spectral analysis code called spamms (Spectroscopic PAtch Model for Massive Stars) specifically designed to analyze non-spherical systems. We discuss how the code works and discuss its assumptions. Furthermore, we demonstrate how spamms can be applied to a variety of different types of systems and we show how it can model 3D effects in a way that current analysis techniques are not able to.

Mass loss through stellar winds plays a dominant role in the evolution of massive stars. Very massive stars (VMSs, > 100Mȯ) display Wolf-Rayet spectral morphologies (WNh) whilst on the main-sequence. Bestenlehner (2020) extended the elegant and widely used stellar wind theory by Castor, Abbott & Klein (1975) from the optically thin (O star) to the optically thick main-sequence (WNh) wind regime. The new mass-loss description is able to explain the empirical mass-loss dependence on the Eddington parameter and is suitable for incorporation into stellar evolution models for massive and very massive stars. The prescription can be calibrated with the transition mass-loss rate defined in Vink & Gräfener (2012). Based on the stellar sample presented in Bestenlehner et al. (2014) we derive a mass-loss recipe for the Large Magellanic Cloud using the new theoretical mass-loss prescription of Bestenlehner (2020).

Hot, massive stars are known to host unstable, radiation-driven outflowing winds, giving rise to dense clumps of material which severely affect the diagnostic techniques used to derive wind properties of massive stars. Most of the current diagnostic models account for wind inhomogeneities by assuming a one-component medium consisting of optically thin clumps, and maintaining a smooth velocity-field. However, this neglects important light-leakage effects through porous channels in-between the clumps. These light-leakage effects have recently been incorporated in the stellar atmosphere modelling code FASTWIND, and here we will present quantitative mass-loss results from a combined Ultraviolet-Optical wind analysis of O-supergiants in the Galaxy. Using a genetic-algorithm fitting-approach, we systematically investigate the impact the wind physics has on derived stellar and wind parameters, and how this depends on metallicity and spectral type. We compare our findings with earlier results (which do not take into account such light-leakage effects), to standard mass-loss rates usually included in evolution model studies of massive stars, and with theoretical predictions of clumping properties. We will also present the first systematic empirical constraints on the new wind parameters, associated with light-leakage, and compare these with theoretical predictions.

Spectroscopy can decode the radiation from stars in an appropriate way and derive many properties of different stellar objects. In this work we seek to derive simultaneously stellar and wind parameters of massive stars. To model the data we use the radiative transport code Fastwind with the hydrodynamic solutions derived using our stationary code Hydwind as input, instead of the β-law. Then, ISOSCELES, our grid of stellar atmosphere and hydrodynamic models of massive stars, is used to derive the physical properties of the observed spectra through spectral line fittings. This quantitative spectroscopic analysis provide an estimation about the line–force parameters, whose theoretical calculations are complex. In addition, we expect to confirm that the hydrodynamic δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and, at the same time, explain disagreements between observational data and theoretical models for the Wind–Momentum Luminosity Relationship (WLR).

We have collected a database of more than 43,000 spectra of atmospheres of massive stars. These spectra have been generated with the CMFGEN code of Hillier & Miller (1998) by systematically varying stellar parameters: effective temperature, luminosity, metallicity and mass loss rate for stars from 9 to 120 solar masses (Zsargó et al. 2020) In this work we present a web-based platform for accessing the database. The platform allows an online comparison between an observed and a synthetic spectrum to quickly assess the stellar and wind parameters. The platform will be available without cost to the astronomical community and will be hosted on servers shared between Mexican Universities.

We present Color Magnitude Diagrams (CMDs) created by using our database of 43,340 synthetic CMFGEN spectra. For each calculated spectra we measure the absolute flux by Johnson and Gaia photometry filters and build synthetic CMDs.

B supergiants (BSGs) lie on the cool end of line-driven wind regime, such that the study of their atmospheres can help us to understand the physics of line-driven winds. So far key features of their spectra, especially in the UV region, could not be reproduced consistently with atmosphere models. This represents a significant gap in our knowledge of their physical properties and behavior, which is particularly striking for BSGs on the cool side of the Bi-Stability Jump (cooler than B1). To address this problem, we analysed a sample of Galactic cool BSGs, with sufficient UV and optical coverage. None of our targets are detected in X-rays with only upper limits existing for some of them.

The core of the cluster R136 in the Large Magellanic Cloud hosts the most massive stars known. The high mass-loss rates of these stars strongly impact their surroundings, as well as the evolution of the stars themselves. To quantify this impact accurate mass-loss rates are needed, however, uncertainty about the degree of inhomogeneity of the winds (‘wind clumping’), makes mass-loss measurements uncertain. We combine optical and ultraviolet HST/STIS spectroscopy of 56 stars in the core of R136 in order to put constraints on the wind structure, improving the accuracy of the mass-loss rate measurements. We find that the winds are highly clumped, and use our measured mass-loss rates to test theoretical predictions. Furthermore we find, for the first time, tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped than those with lower mass-loss rates.

We perform spectral fittings for O-type stars based on self-consistent wind solutions, providing Ṁ and ν(r directly derived from the initial stellar parameters. We introduce our two methods: m-CAK prescription and Lambert-procedure.

The Lambert-procedure allows the calculation of consistent v(r) that reduce the number of free parameters when a spectral fitting using CMFGEN is performed, even without recalculation of the Ṁ. Spectra calculated from our Lambert-solutions show significant differences compared to the initial β-law CMFGEN models. For m-CAK prescription, self-consistent solutions provide values for theoretical Ṁ on the order of the most recent predictions from other studies. Later, we find a global fit with the RT code FASTWIND. This is an important step towards the determination of stellar and wind parameters without using β-law. Our m-CAK prescription is valid for the O-type stars with Teff ≥ 30 kK and log g ≥ 3.2.

We expect that solutions introduced here to be extended to numerous studies about massive stars in future.

One significant difficulty in reliable quantification of the rates of mass-loss from hot, massive stars lies in uncertainties associated with quantifying temporal and spatial variability within stellar winds. The consequences of low-metallicity conditions for wind structure also merit continued investigation. We present initial results from ULLYSES data with the aim of identifying structure within the stellar winds of early B type supergiants with sub-solar metallicities in the Large and Small Magellanic Clouds. We demonstrate how single-epoch ULLYSES data can be used to investigate significant wind structure for these stars.

Mass-loss is a key parameter throughout the evolution of massive stars. In this work we probe the radial clumping stratification of OB stars in the intermediate and outer wind regions (r ≳ 2R*; r, radial distance to photosphere), derive upper limits for mass-loss rates, Ṁmax, and compare them to current theoretical mass-loss recipes implemented in evolutionary models. A key conclusion of our analysis regards the derived upper-limit mass-loss rates of B supergiants, independently of clumping, which calls for an urgent revision of the role recombination of iron-like elements plays in determining the mass-loss rates of objects that cross the bi-stability region, and a careful analysis of corresponding effects for stellar evolution models.

Massive stars are the objects that condition the evolution of the interstellar medium by the amount of energy released during their lives and especially by their death as a supernova explosion. All the data provided by the previous and ongoing missions of ground and space telescopes have saturated us with the amount of information, which is no longer easy to process daily by human routines. To this end, we present the development of a massive star spectroscopic interactive database designed for scientific research.

B-type supergiants show enormous potential as resourceful tools to address a wide range of astrophysical questions concerning stellar atmospheres, stellar and galactic evolution and the cosmic distance scale. For the purposes of a comprehensive analysis of these objects we test a hybrid non-LTE approach – line-blanketed model atmospheres computed under the assumptions of local thermodynamic equilibrium (LTE) in combination with non-LTE line-formation calculations. An observational sample of 14 Galactic B-type supergiants with masses below about 30 Mȯ is investigated on the basis of high-resolution Echelle spectra. The results of this analysis – atmospheric and fundamental stellar parameters, the characterisation of the interstellar sightlines to the objects, as well as derived spectroscopic distances and multi-species abundances – are subjected to multiple tests of consistency.