We highlight a few results from ALMA Band 6 observations of high-rotational transition number (J) SiO masers towards oxygen-rich AGB and red supergiant stars carried out as part of the ATOMIUM Large Programme in 2018–2020. A search for a relationship between mass-loss rates and flux-weighted mean angular distances of maser components was inconclusive, as linear regression models for the 28SiO v=1 J =5–4 and J =6–5 transitions were inconsistent. Supplementary APEX observations towards the ATOMIUM AGB stars also suggest variability at different stellar pulsation phases.

This contribution presents new results on two members of the class of post-Red Supergiants, IRAS 17163-3907, the central star of the Fried Egg nebula and IRC +10420. New optical spectra in the blue spectral range confirm their spectral type to be of A-supergiant class. Our VLTI/GRAVITY K-band interferometry reveals that the neutral Na i 2.2 μm line emitting region is smaller than that of the hydrogen Brγ emission. This can be explained with the hydrogen emission the result of collisional excitation populating the higher levels in a neutral region instead them being populated through recombination in an ionised environment as mostly inferred in stellar winds. Finally, the central star of the Fried Egg nebula, has undergone 3 distinct mass loss episodes over the last hundreds of years. As it is likely that at least the last mass loss event occurred when the star was already a Yellow Hypergiant and not a Red Supergiant, we put forward the bi-stability mechanism as explanation for the mass loss.

Supernova properties in radio strongly depend on their circumstellar environment and they are an important probe to investigate the mass loss of supernova progenitors. Recently, core-collapse supernova observations in radio have been assembled and the rise time and peak luminosity distribution of core-collapse supernovae in radio has been obtained. In this talk, we will discuss the constraints on the mass-loss prescriptions of red supergiants obtained from the assembled radio properties of Type II supernovae. We take a couple of mass-loss prescriptions for red supergiants, calculate the rise time and peak luminosity distribution based on them, and compare the results with the observed distribution. We found that the widely spread radio rise time and peak luminosity distribution of Type II supernovae can only be explained by mass-loss prescriptions having strong dependence on the luminosity. Red supergiant mass-loss prescriptions should have steep luminosity dependence in the supernova progenitor range.

Due to observational constraints, our detailed knowledge of stellar populations, formation, and evolution of galaxies is limited to a few dozen galaxies located in the Local Group. The Local Group of galaxies offers a unique opportunity to construct the formation histories and probe the structure and dynamics of many dwarf galaxies surrounding the Milky Way and Andromeda and of isolated dwarf galaxies. In this regard, we monitored the majority of galaxies in the Local Group, including the M33 galaxy and satellites galaxies surrounding the Milky Way and Andromeda galaxy, as well as isolated dwarf galaxies. We identified stellar populations and based on light curve analysis, the cool evolved stars pulsating in the fundamental mode were identified. In this paper, first, we will present the results we obtained for SFH and dust production rate in individual galaxies separately to answer how different types of galaxies have been formed and evolved over cosmic time. Then, we will discuss whether the mass return from dusty evolved stars can provide enough gas reservoirs to sustain the star formation or even rejuvenate the dwarf galaxy, as some seem to harbor relatively young stars.

Red supergiants (RSGs) are evolved massive stars in a stage preceding core-collapse supernova. Understanding evolved-phases of these cool stars is key to understanding the cosmic matter cycle of our Universe, since they enrich the cosmos with newly formed elements. However, the physical processes that trigger mass loss in their atmospheres are still not fully understood, and remain one of the key questions in stellar astrophysics. We use a new method to study the extended atmospheres of these cold stars, exploring the effect of a stellar wind for both a simple radiative equilibrium model and a semi-empirical model that accounts for a chromospheric temperature structure. We then can compute the intensities, fluxes and visibilities matching the observations for the different instruments at the Very Large Telescope Interferometer (VLTI). Specifically, when comparing with the atmospheric structure of HD 95687 based on published VLTI/AMBER data, we find that our model can accurately match these observations in the K-band, showing the enormous potential of this methodology to reproduce extended atmospheres of RSGs.

Local Group (LG), the nearest and most complete galactic environment, provides valuable information on the formation and evolution of the Universe. Studying galaxies of different sizes, morphologies, and ages can provide this information. For this purpose, we chose the And IX dSph galaxy, which is one of the observational targets of the Isaac Newton Telescope (INT) survey. A total of 50 long-period variables (LPVs) were found in And IX in two filters, Sloan i' and Harris V at a half-light radius of 2.5 arcmin. The And IX’s star formation history (SFH) was constructed with a maximum star formation rate (SFR) of about 0.00082 ± 0.00031 M⊙ yr−1, using LPVs as a tracer. The total mass return rate of LPVs was calculated based on the spectral energy distribution (SED) of about 2.4 × 10−4 M⊙ yr−1. The distance modulus of 24.56−0.15+0.05 mag was estimated based on the tip of the red giant branch (TRGB).

From November 2019 to April 2020, the prototypical red supergiant Betelgeuse experienced an unexpected and historic dimming. This event was observed worldwide by astrophysicists, and also by the general public with the naked eye. We present here the results of our observing campaign with ESO’s VLT and VLTI in the visible and infrared domains. The observations with VLT/SPHERE-ZIMPOL, VLT/SPHERE-IRDIS, VLTI/GRAVITY and VLTI/MATISSE provide spatially resolved diagnostics of this event. Using PHOENIX atmosphere models and RADMC3D dust radiative transfer simulations, we built a consistent model reproducing the images and the photometry.

We run numerical simulations of massive colliding wind binaries, and quantify the accretion onto the secondary under different conditions. We set 3D simulation of a LBV–WR system and vary the LBV mass loss rate to obtain different values of wind momentum ratio η. We show that the mean accretion rate for stationary systems fits a power law Macc∝ η–1.6 for a wide range of η, until for extremely small η saturation in the accretion is reached. We find that the stronger the primary wind, the smaller the opening angle of the colliding wind structure (CWS), and compare it with previous analytical estimates. We demonstrate the efficiency of clumpy wind in penetrating the CWS and inducing smaller scale clumps that can be accreted. We propose that simulations of colliding winds can reveal more relations as the ones we found, and can be used to constrain stellar parameters.

Close binary evolution is widely invoked to explain the formation of axisymmetric planetary nebulae, after a brief common envelope phase. The evolution of the primary would be interrupted abruptly, its still quite massive envelope being fully ejected to form the PN, which should be more massive than a planetary nebula coming from the same star, were it single. We test this hypothesis by investigating the ionised and molecular masses of a sample consisting of 21 post-common-envelope planetary nebulae, roughly one fifth of their known total population, and comparing them to a large sample of regular planetary nebulae (not known to host close-binaries). We find that post-common-envelope planetary nebulae arising from single-degenerate systems are, on average, neither more nor less massive than regular planetary nebulae, whereas post-common-envelope planetary nebulae arising from double-degenerate systems are considerably more massive, and show substantially larger linear momenta and kinetic energy than the rest. Reconstruction of the common envelope of four objects further suggests that the mass of single-degenerate nebulae actually amounts to a very small fraction of the envelope of their progenitor stars. This leads to the uncomfortable question of where the rest of the envelope is, raising serious doubts on our understanding of these intriguing objects.

This contribution focuses on a rare example of the class of post-Red Supergiants, IRAS 17163-3907, the central star of the Fried Egg nebula. In particular, we discuss some of our recently published results in detail. The inner parts of the circumstellar environment of this evolved massive star are probed at milli-arcsec resolution using VLTI’s GRAVITY instrument operating in the K-band (2 µm), while larger, arcsecond, scales are probed by VISIR diffraction limited images around 10 µm, supplemented by a complete Spectral Energy Distribution. The spectro-interferometric data cover important diagnostic lines (Brγ, Na I), which we are able to constrain spatially. Both the presence and size of the Na i doublet in emission has been traditionally challenging to explain towards other objects of this class. In this study we show that a two-zone model in Local Thermal Equilibrium can reproduce both the observed sizes and strengths of the emission lines observed in the K-band, without the need of a pseudo-photosphere. In addition, we find evidence for the presence of a third hot inner shell, and demonstrate that the star has undergone at least three mass-loss episodes over roughly the past century. To explain the properties of the observed non-steady mass-loss we explore pulsation-driven and line-driven mass-loss and introduce the bi-stability jump as a possible underlying mechanism to explain mass-loss towards Yellow Hypergiants.

We derive azimuthally-averaged surface-brightness profiles of 16 AGB stars in the far-IR and sub-mm with the aim of studying the resolved historic mass loss in the extended circumstellar envelope. The PSF-subtracted extended component fluxes were found to be ∼40% of the total source flux. By fitting SEDs at each radial point we derive the dust temperature, column density and spectral index of emissivity via Bayesian inference. The measured dust-to-gas ratios were somewhat consistent with canonical values however with a large scatter.

We report on the successful search for CO (2-1) and (3-2) emission associated with OH/IR stars in the Galactic Bulge. We observed a sample of eight extremely red AGB stars with the APEX telescope and detected seven. The sources were selected at sufficient high Galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. We also collected photometric data and Spitzer IRS spectroscopy to construct the SEDs, which were analysed through radiative transfer modelling. We derived variability periods of our stars from the VVV and WISE surveys. Through dynamical modelling we then retrieve the total mass loss rates (MLR) and the gas-to-dust ratios. The luminosities range between approximately 4,000 and 5,500 L⊙ and periods are below 700 days. The total MLR ranges between 10−5 and 10−4 M⊙ yr−1. The results are presented in Blommaert et al. 2018 and summarized below.

Hot star winds are driven by the radiative force due to light absorption in lines of heavier elements. Therefore, the amount of mass lost by the star per unit of time, i.e., the mass-loss rate, is sensitive to metallicity. We provide mass-loss rate predictions for O stars with mass fraction of heavier elements 0.2 <Z/Z⊙ ≤ 1. Our predictions are based on global model atmospheres. The models allow us to predict wind terminal velocity and the mass-loss rate just from basic global stellar parameters. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as (Z/Z⊙)0.59. The predicted mass-loss rates agree with mass-loss rates derived from ultraviolet wind line profiles. At low metallicity, the rotational mixing affects the wind mass-loss rates. We study the influence of magnetic line blanketing.

A small subset of Galactic O-stars possess surface magnetic fields that alter the outflowing stellar wind by magnetically confining it. Key to the magnetic confinement is that it induces rotational modulation of spectral lines over the full EM domain; this allows us to infer basic quantities, e.g., mass-loss rate and magnetic geometry. Here, we present an empirical study of the Hα line in Galactic magnetic O-stars to constrain the mass fed from the stellar base into the magnetosphere, using realistic multi-dimensional magnetized wind models, and compare with theoretical predictions. Our results suggest that it may be reasonable to use mass-feeding rates from non-magnetic wind theory if the absolute mass-loss rate is scaled down according to the amount of wind material falling back upon the stellar surface. This provides then some empirical support to the proposal that such magnetic O-stars might evolve into heavy stellar-mass black holes (Petit et al.2017).

We present ALMA observations of the circumstellar envelope around the AGB carbon star TX Psc in molecular CO(2–1) emission, and detect a previously unknown detached shell with filamentary structure and elliptical shape. Up to now, all observed detached shells are found around carbon AGB stars and are of remarkable spherical symmetry. The elliptical shell around TX Psc is the first clear exception to that rule, with TX Psc being classified as rather ’’fresh’’ carbon star, that most likely has only experienced very few thermal pulses yet. We investigate and discuss the 3D structure of the CSE and its most likely formation scenarios, as well as the link of this peculiar detached shell to the AGB evolutionary status of TX Psc.

We present JHK observations of the metal-poor $$(\left[ {{\rm{Fe}}/{\rm{H}}} \right] < - 1.40)$$ dwarf-irregular galaxies, Leo A and Sextans A, obtained with the WIYN High-resolution Infrared Camera. Their near-IR stellar populations are characterized by using a combination of color-magnitude diagrams and by identifying long-period variable (LPV) stars. We detected red giant and asymptotic giant branch (AGB) stars, consistent with membership of the galaxy’s intermediate-age populations (2-8 Gyr old). We identify 32 dusty evolved stars in Leo A and 101 dusty stars in Sextans A, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The majority of this dust is produced by a few very dusty evolved stars.

We aim to analyse the co-added Herschel images of various categories of evolved stars in the LMC and SMC from the Herschel HERITAGE survey in order to identify, in a statistical sense, a cool historic dust mass component emitted by these sources. The fluxes derived from the co-added stacks can then be compared with those predicted by the GRAMS model grid in order to refine the DPRs estimated for the SMC and LMC.

Winds of hot stars are driven by the radiative force due to absorption of light in the lines of heavier elements. Consequently, the mass-loss rate and the wind velocity depend on the ionization state of the wind. As a result of this, there is a feedback between the ionizing X-ray source and the stellar wind in HMXBs powered by wind accretion. We study the influence of the small-scale wind structure (clumping) on this feedback using our NLTE hydrodynamical wind models. We find that clumping weakens the effect of X-ray irradiation. Moreover, we show that the observed X-ray luminosities of HMXBs can not be explained by wind accretion scenario without introducing the X-ray feedback. Taking into account the feedback, the observed and estimated X-ray luminosities nicely agree. We identify two cases of X-ray feedback with low and high X-ray luminosities that can explain the dichotomy between SFXTs and sgXBs.

With red supergiants (RSGs) predicted to end their lives as Type IIP core collapse supernova (CCSN), their behaviour before explosion needs to be fully understood. Mass loss rates govern RSG evolution towards SN and have strong implications on the appearance of the resulting explosion. To study how the mass-loss rates change with the evolution of the star, we have measured the amount of circumstellar material around 19 RSGs in a coeval cluster. Our study has shown that mass loss rates ramp up throughout the lifetime of an RSG, with more evolved stars having mass loss rates a factor of 40 higher than early stage RSGs. Interestingly, we have also found evidence for an increase in circumstellar extinction throughout the RSG lifetime, meaning the most evolved stars are most severely affected. We find that, were the most evolved RSGs in NGC2100 to go SN, this extra extinction would cause the progenitor’s initial mass to be underestimated by up to 9M⊙.

Massive star winds greatly influence the evolution of both their host star and local environment though their mass-loss rates, but current radiative line-driven wind models do not incorporate any magnetic effects. Recent surveys of O and B stars have found that about ten percent have large-scale, organized magnetic fields. These massive-star magnetic fields, which are thousands of times stronger than the Sun’s, affect the inherent properties of their own winds by changing the mass-loss rate. To quantify this, we present a simple surface mass-flux scaling over the stellar surface which can be easily integrated to get an estimate of the mass-loss rate for a magnetic massive star. The overall mass-loss rate is found to decrease by factors of 2-5 relative to the non-magnetic CAK mass-loss rate.