We present our measurements of the amplitude of photometric and spectroscopic variability due to clumping in the wind of Wolf-Rayet (WR) stars. Photometric variability was assessed using TESS light-curves, while spectroscopic variations were obtained from almost 20 years of monitoring of nearly 100 classical (presumably single) stars. Our results show an apparent dependence of the variability amplitude with the stars’ surface temperature and/or terminal velocity. Our interpretation is that it supports the idea that the dominating driver of the clumps in WR winds is a sub-surface convection region.

Mass loss is a key property to understand stellar evolution and in particular for low-metallicity environments. Our knowledge has improved dramatically over the last decades both for single and binary evolutionary models. However, episodic mass loss although definitely present observationally, is not included in the models, while its role is currently undetermined. A major hindrance is the lack of large enough samples of classified stars. We attempted to address this by applying an ensemble machine-learning approach using color indices (from IR/Spitzer and optical/Pan-STARRS photometry) as features and combining the probabilities from three different algorithms. We trained on M31 and M33 sources with known spectral classification, which we grouped into Blue/Yellow/Red/B[e] Supergiants, Luminous Blue Variables, classical Wolf-Rayet and background galaxies/AGNs. We then applied the classifier to about one million Spitzer point sources from 25 nearby galaxies, spanning a range of metallicites (). Equipped with spectral classifications we investigated the occurrence of these populations with metallicity.

We present low-frequency (0.40 – 1.25 GHz) radio observations and modeling of a Fast Blue Optical Transient (FBOT), AT2018cow [Nayana & Chandra(2021)]. Our data are best modeled as an inhomogeneous synchrotron emitting region expanding into an ionized circumstellar medium. We estimate the mass-loss rate of the progenitor star and shock parameters at multiple epochs post-explosion and find that the progenitor has gone through an enhanced phase of mass-loss close to its end-of-life.

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⊙.

We compare pre-supernova observations with synthetic photometry from stellar evolution models to infer the progenitor properties of the seven known progenitors of Type Ib and IIb supernovae. Our results are roughly consistent with a hydrogen mass threshold of for a Type II appearance.

Recent observations of Type II supernovae have revealed that their red-supergiant progenitors lose a significant amount of mass during the last years of their evolution. However, because it is difficult to discover supernovae within days of explosion, the diversity of mass loss in red supergiants has not yet been fully mapped. This talk presented the case of SN 2021yja, which was serendipitously imaged within hours of explosion and observed with a sub-day cadence during its rise to peak. From the exceptionally long plateau period and the high nickel mass, we infer a relatively massive red-supergiant progenitor star. However, archival imaging from the Hubble Space Telescope places a stringent upper limit of on its progenitor mass. We discuss these conflicting constraints in the context of the larger sample of exploding red supergiants. Our analysis helps illuminate the poorly understood mechanism(s) behind red-supergiant mass loss.

The recent generation of dedicated wide-field, high-cadence sky-surveys have overwhelmed discovery statistics for all manner of extra-galactic transients, and uncovered new phenomena seemingly linked to the demise of massive stars. For the more established classes of transients, such as core-collapse supernovae, surges in discoveries are allowing true population studies to provide quantitative constraints not only on the explosion properties, but also on the progenitor populations. Crucially, such population insights are benefiting from creation of samples of transients constructed with largely unbiased methods for discovery and characterisation. Surrounding these discoveries are increasing samples of extreme transients that do not fit the standard core-collapse paradigm - requiring the invocation of exotic progenitor stars and placing demands on the stellar evolution of such systems. Here I will provide a high-level observationally-driven overview of recent results related to massive stellar transients.

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

We present in-progress resolution test and parameter space studies for very massive stars using MESA, showcasing current MESA version convergence studies.

We present the analysis of the dust properties of the Wolf-Rayet nebulae M 1-67 and RCW 58 around the WN8h stars WR 124 and WR 40, respectively. Modeling with the photoionization code Cloudy shows that in both nebulae the IR spectral energy distributions and ionized gas properties can be reproduced by a dust shell consisting of two populations of dust grains. Furthermore, taking into account the initial mass, the morphology and the kinematics of the nebulae we propose M 1-67 and RCW 58, together with their progenitor stars, as the first observational evidences of post-common envelope evolution in nebulae around massive stars.

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.

A century of study has characterized Plaskett’s Star (HD 47129) as an evolved, massive, short-period, equal mass O+O binary system. The discovery of a magnetic field in the broad-line component by Grunhut et al. (2013) renewed interest in the study of this system and led to its establishment as the most rapidly rotating magnetic O-type star. Grunhut et al. (2021) observed the circular polarization signatures of the magnetic star to exhibit no radial velocity variations while the narrow-line star demonstrates radial velocity variations consistent with the established orbital period. This has raised fundamental questions about the architecture of this system and the nature of the magnetic star which have led to a major shift in our understanding of HD 47129.

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.

Our knowledge of massive star evolution is limited by uncertainties linked with multi-dimensional processes taking place in stellar interiors. Important examples are convective boundary mixing (CBM) and entrainment, which are implemented in 1D stellar evolution models assuming simplified prescriptions. 3D hydrodynamics models can improve these prescriptions by studying realistic multi-D processes for a short timerange (minutes or hours). In these proceedings, we present results coming from a new set of high-resolution hydrodynamics simulations of a neon-burning shell in a massive star, and discuss how the entrainment law can be calibrated from 3D models and then used to improve 1D stellar evolution prescriptions.

Especially in the upper Hertzsprung-Russell diagram, where stellar physics is least understood, obtaining model independent masses is of great value. Spectroscopic binaries that are also resolved astrometrically are an excellent alternative to eclipsing double-lined spectroscopic binaries where dynamical masses can be measured. 9 Sgr is such a massive binary. However, its characterization is troubled by conflicting conclusions from the spectroscopic analysis on the one hand and the interferometric one on the other hand. In this work, we attempt to resolve this tension by applying a novel approach to spectral disentangling of the spectroscopic data to constrain better the mass of 9 Sgr.

Direct observations of the products of binary interactions are sparse, yet they provide important insights on the outcome of the interaction and the physics at play. Young and intermediate-age star clusters are the ideal tool to search for, and characterize such interaction products and allow for a detailed comparison to theoretical predictions. We here report on integral field spectroscopy obtained with MUSE for several such clusters in the Magellanic Clouds.

We analyzed archival HST and IUE ultraviolet spectra of 29 nearby star-forming galaxies. The range of aperture sizes permits studies of the galaxy properties over pc to kpc scales. We measured line strengths and spectral energy distributions over the 1200 – 1300 Åwavelength range and established trends with galaxy properties. Updated oxygen abundances were measured from ancillary optical data. Star-formation rates and internal dust attenuations were derived from comparison with synthesis models. The interstellar absorption lines are heavily saturated, yet scale with oxygen abundance. We interpret this as due to macroscopic velocities arising in a turbulent ISM and large-scale outflows. The stellar-wind lines also scale with oxygen abundance. As these lines are shaped by mass loss, which is driven by the Fe abundance, we can study the α-element/Fe ratio in these galaxies.

Local HII environment metallicities of 65 supernovae (SNe), obtained with INT/IDS, have been determined using the N2 and O3N2 strong emission line methods. Resulting cumulative distribution functions reveal a narrower distribution for Ib SNe (standard deviation σ ∼ 0.06 dex) compared to Ic and IIP distributions (σ ∼ 0.15 dex). This narrow distribution of Ib SNe is confirmed with an extended dataset using data from Galbany et al. (2018). Statistical tests confirm a statistically significant difference between the Ib and II-P metallicity distributions with < 5% probability that they result from the same progenitors. This narrow distribution suggests a lack of Type Ib SNe in low metallicity environments and points towards single star progenitors for these Type Ib SNe, rather than binaries. It also suggests that single massive stars at low metallicity are not commonly able to produce helium-rich Type Ib supernovae.

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.

The empirical upper limit to Red Supergiant (RSG) luminosity, known as the Humphreys-Davidson (HD) limit, has been commonly explained as being caused by the stripping of stellar envelopes by metallicity-dependent, line-driven winds. As such, the theoretical expectation is that the HD limit should be higher at lower metallicity, where weaker mass-loss rates mean that higher initial masses are required for an envelope to be stripped. In this work, we test this prediction by measuring the luminosity function of RSGs in M31 and comparing to those in the LMC and SMC. We find that $\[\log ({L_{{\rm{m}}ax}}/{L_ \odot }) = 5.53 \pm 0.03\]$ in M31 (Z ≳ Z⊙), consistent with the limit found for both the LMC (Z ∼ 0.5 Z⊙) and SMC (Z ∼ 0.25 Z⊙), while the RSG luminosity distributions in these 3 galaxies are consistent to within 1σ. We therefore find no evidence for a metallicity dependence on both the HD limit and the RSG luminosity function, and conclude that line-driven winds on the main sequence are not the cause of the HD limit.