Low- and intermediate mass stars experience a significant mass loss during the last phases of their evolution, which obscures them in a vast, dusty envelope. Although it has long been thought this envelope is generally spherically symmetric in shape, recent high-resolution observations find that most of these stars exhibit complex and asymmetrical morphologies, most likely resulting from binary interaction. In order to improve our understanding about these systems, theoretical studies are needed in the form of numerical simulations. Currently, a handful of simulations exist, albeit they mainly focus on the hydrodynamics of the outflow. Hence, we here present the pathway to more detailed and accurate modelling of companion-perturbed outflows with, by discussing the missing but crucial physical and chemical processes. With these state-of-the-art simulations we aim to make a direct comparison with observations to unveil the true identity on the embedded systems.

A recent analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way (MW) identified a kink in the initial-final mass relation (IFMR), located over a range of initial masses, 1.65 ≲ Mi/M⊙ ≲ 2.10, which unexpectedly interrupts the commonly assumed monotonic trend. The proposed interpretation links this observational fact to the formation of carbon stars and the modest outflows (with mass loss rate < 10−7 M⊙/yr) that are expected as long as the carbon excess remains too low to produce dust grains in sufficient amount. Under these conditions the mass of the carbon-oxygen core can grow more than is generally predicted by stellar models. We discuss these new findings also in light of a new systematic follow-up investigation, based on Gaia EDR3, of evolved giants (13 carbon stars, 3 S stars and 4 M stars) belonging to intermediate-age open clusters.

Some binary stars experience common envelope evolution, which is accompanied by drastic loss of angular momentum, mass, and orbital energy and which leaves behind close binaries often involving at least one white dwarf, neutron star, or black hole. The best studied phase of common envelope is the dynamical inspiral lasting few original orbital periods. We show theoretical interpretation of observations of V1309 Sco and AT2018bwo revealing that binaries undergo substantial prolonged mass loss before the dynamical event amounting up to few solar masses. This mass loss is concentrated in the orbital plane in the form of an outflow or a circumbinary disk. Collision between this slower mass loss and the subsequent faster dynamical ejection powers a bright red transient. The resulting radiative shock helps to shape the explosion remnant and provides a site of dust and molecule formation.

Understanding the nucleosynthetic origin of nitrogen and the evolution of the N/O ratio in the interstellar medium is crucial for a comprehensive picture of galaxy chemical evolution at high-redshift because most observational metallicity (O/H) estimates are implicitly dependent on the N/O ratio. The observed N/O at high-redshift shows an overall constancy with O/H, albeit with a large scatter. We show that these heretofore unexplained features can be explained by the pre-supernova wind yields from rotating massive stars (M≳10M⊙,ν/νcrit≳0.4). Our models naturally produce the observed N/O plateau, as well as the scatter at low O/H. We find the scatter to arise from varying star formation efficiency. However, the models that have supernovae dominated yields produce a poor fit to the observed N/O at low O/H. This peculiar abundance pattern at low O/H suggests that dwarf galaxies are most likely to be devoid of SNe yields and are primarily enriched by pre-supernova wind abundances.

The cosmic origin of fluorine is still under debate. Asymptotic giant branch (AGB) stars are among the few suggested candidates to efficiently synthesis F in our Galaxy, however their relative contribution is not clear. In this paper, we briefly review the theoretical studies from stellar yield models of the F synthesis and chemical equilibrium models of the F-containing molecules in the outflow around AGB stars. Previous detections of the F-bearing species towards AGB and post-AGB stars are also highlighted. We suggest that high-resolution ALMA observations of the AlF, one of the two main carriers of F in the outflow of AGB stars, can provide a reliable tracer of the F-budget in AGB stars. This will be helpful to quantify the role of AGB stars in the Galactic F budget.

Evolved massive stars are major cosmic engines, providing strong mechanical and radiative feedback on their host environment. They contribute to the enrichment of their environment through a strong stellar winds, still poorly understood. Wind physics across the life cycle of these stars is the key ingredient to accomplish a complete understanding of their evolution in the near and distant Universe. Nowadays, the development of the observational instruments is so advanced that the observations became very sensitive to the details of the stellar surface making possible to quantitatively study what happens on their surfaces and above where the stellar winds become dominant. Three-dimensional radiative hydrodynamics simulations of evolved stars are essential to a proper and quantitative analysis of these observations. This work presents how these simulations have been (and will be) crucial to prepare and interpret a multitude of observations and how they are important to achieve the knowledge of the mass-loss mechanism.

Most of a star’s mass is bound in a hydrostatic equilibrium in which pressure balances gravity. But if at some near-surface layer additional outward forces overcome gravity, this can transition to a supersonic, outflowing wind, with the sonic point, where the outward force cancels gravity, marking the division between hydrostatic atmosphere and wind outflow. This talk will review general issues with such transonic initiation of a stellar wind outflow, and how this helps set the wind mass loss rate. The main discussion contrasts the flow initiation in four prominent classes of steady-state winds: (1) the pressure-driven coronal wind of the sun and other cool stars; (2) line-driven winds from OB stars; (3) a two-stage initiation model for the much denser winds from Wolf-Rayet (WR) stars; and (4) the slow “overflow” mass loss from highly evolved giant stars. A follow on discussion briefly reviews eruptive mass loss, with particular focus on the giant eruption of η Carinae.

We present interferometric continuum and molecular line emission maps obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of OH231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star that is key to understand the remarkable changes in nebular morphology and kinematics during the short transition from the AGB to the Planetary Nebula (PN) phase. The excellent angular resolution of our maps (∼20 mas ∼30 AU) allows us to scrutinize the central nebular regions of OH231.8+4.2, which hold the clues to understanding how this iconic object assembled its complex nebular architecture. We report, for the first time in this object and others of its kind (i.e. pre-PNe with massive bipolar outflows), the discovery of a rotating circumbinary disk of radius ∼30 AU traced by NaCl, KCl, and H2O emission lines. The disk lies at the base of a young bipolar wind with signs of rotation as well. A compact spatially resolved dust disk is found perpendicular to the bipolar outflow. We also identify a point-like continuum source, which likely represents the central Mira star enshrouded by a ∼3 R* shell or disk of hot (∼1400 K) freshly formed dust. The point source is slightly off-centre from the disk centroid, enabling us for the first time to place constraints to the orbital separation of the central binary system.

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.

To decode the information stored within a spectrum, detailed modelling of the physical state is required together with accurate radiative transfer solution schemes. In the analysis of stellar spectra, the numerical model often needs to account for high velocity outflows, multi-dimensional structures, and the effects of binary companions. Focusing now on binary systems, we present the BOSS-3D spectral synthesis code, which is capable of calculating synthetic line profiles for a variety of binary systems. Assuming the state of the circumstellar material to be known, the standard pz-geometry is extended by defining individual coordinate systems for each object. By embedding these coordinate systems within the observer’s frame, BOSS-3D automatically accounts for outflows or discs within both involved systems, and includes all Doppler shifts. Moreover, the code accounts for different length-scales, and thus could also be used to analyse transit-spectra of planetary atmospheres. As a first application of BOSS-3D, we model the phase-dependent line profiles for the enigmatic binary (or multiple) system LB-1.

A significant fraction of the stars near the tip of the AGB phase become regular or semi-regular (Mira-type, SRs) pulsators. However, some of these light curves have shown intriguing secondary minima or sharp dips with much longer periods. Although this phenomenon shows some resemblance with the R CrB variables, the light curve is generally symmetric before and after the dip, whereas in R CrB the luminosity recovers slower after its minimum. More recently, high-resolution ALMA CO observations revealed a spiral structure around some of these stars, which suggests the presence of a stellar or sub-stellar companion. In these cases, the long-term light curve minima could be caused by periodic eclipses of the primary by a spiral circumstellar structure, and the long-period would be related to the orbital period. In this paper we discuss the pros and cons of the various proposed scenarios for the long-term minima of pulsating AGB stars.