La Serena, Chile, November 30 - December 4, 2020

Scientific Rationale

Mass loss is one of the most important factors in the post main sequence evolution, making low- and intermediate-mass stars crucial contributors to the chemical enrichment of the Universe. Although the mass-loss process on the AGB has been studied for over 40 years, many basic aspects are still not understood. This is especially the case for the geometry of the process and how it influences the following phase of stellar evolution when the star expels its envelope as a planetary nebula (PN). Although ≈ 70% of the observed PNe are not spherically symmetric, and neither are the winds of post-AGB objects, the AGB wind morphology is widely regarded as such.

In our current understanding, the mass-loss process from single AGB stars develops in two steps: i) the atmosphere is levitated by shock waves caused by stellar pulsation; ii) radiation pressure on dust grains which form in the outer atmospheric layers then triggers the stellar wind which expands following a global spherically symmetric geometry.

So far, the most accepted explanation that accounts for the asymmetries observed in the PN phase is the presence of a nearby companion in the environment of the mass-losing star, which either directly, by gravity alone, or by stimulating a magnetic field, may cause a variety of CSE shaping. Observations of an interaction between a companion and stellar wind on the AGB were only successful for a handful of objects. The presence of binary is inferred via observations of asymmetric structures observed at very large scales in the AGB wind (mainly spirals and biconical outflows), excess towards shorter wavelengths, composite spectra in the case of interacting binaries. There is however a large population of binary companions which is not yet discovered, these are the objects within 10-50 AUs. Thanks to the progress in high-angular-resolution techniques (ALMA, VLT and VLTI) spanning different wavelength ranges, we are now able to spatially resolve the wind of AGB stars from the stellar surface to the interface with the interstellar medium, and to follow and characterize the various dynamical mechanisms that produce the stellar outflows. Indirect signature of the presence of previously unseen binary companions are becoming more frequent, challenging our understanding of the stellar wind mechanism.

The aim of this workshop is to bring together the community of observers and theoreticians working on single and binary evolved stars. We will concentrate on the effects of binaries on AGB stellar evolution. At this mass range, such effects are known but have so far often been neglected. However, contributions on this science scheme related to other evolved stars, such as red supergiants, will be considered as well.
We plan to have two days dedicated to the presentations of recent results in the field of stellar wind from single AGB. We will then dedicate two days to the results on symbiotic and nearby non-interacting binaries. Symbiotic stars (hereafter SySs) are long-period interacting binaries composed of a hot compact star – generally a white dwarf – and an evolved giant star, whose mutual interaction via accretion processes is at the origin of extended emission recorded from the radio to the X-ray regime. SySs represent unique laboratories for studying a variety of important astrophysical problems and their reciprocal influence: e.g., nova-like thermonuclear outbursts, formation and collimation of jets, planetary nebulae morphology, and variable X-ray emission. As binary systems, they offer a powerful benchmark to study the effect of binary evolution on the nucleosynthesis, mixing and dust mineralogy which characterize the AGB companion, likely different from what expected in single AGB stars; moreover, they have even been proposed as potential progenitors of type Ia supernovae. We will conclude with the results on the effect of distant binaries on the wind. The presentations will target different techniques and the corresponding modelling. We will be able to share technical, observational, and modeling expertise in both the fields of stellar wind in single stars and binaries. We will discuss how the different communities (VLT, VLTI, ALMA, HST/JWST) deal with the caveats in the modelling and with the physical interpretation of the observations.

Conference venue

The conference will be held in La Serena, which is the second oldest city in Chile (founded in 1544), and one of the largest in the country. It preserves many buildings of colonial style, many of them being important National Monuments. Today the city is seeing a marked development around tourism, thanks to beautiful beaches, a good climate and attractive places in its vicinity. Handicrafts and typical products from the region, such as pisco and papayas can be found in the popular ‘La Recova’ market.

According to its mission statement, University of La Serena ‘is a regional university of the State of Chile, committed to the Coquimbo Region, which focuses its work in the areas of science, technology, humanities and social sciences.’ In its current form, the University was established in 1981 by merging the former regional headquarters of the Technical University of the State and the University of Chile.

The Salon Pentagono at the Campus Andres Bello of University of La Serena will receive up to 80 participants who register for the workshop.

Proceedings

TBC

Conference email: binagb2020@eso.org

Organizers: ESO, Universidad de La Serena

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