Letters of Intent received in 2016

LoI 2018-1897
Focus Meeting: Massive star evolution in the era of big surveys

Topics

- how to compare massive star models and observations in the era of big surveys
- challenges in massive star evolution, such as effects from mass loss and binarity
- atmospheric modeling of massive stars in different evolutionary stages, such as O-type, LBV, and WR phases
- massive star results from recent surveys such as GAIA
- how the future generation of surveys will constrain massive star evolution

Rationale

The massive star field is undergoing an era of significant progress from both theoretical and observational perspectives. In recent years, there has been a growing appreciation in our community regarding the interplay of mass loss and binary interaction, and how they profoundly influence our understanding of how massive stars evolve and die. From a theoretical standpoint, numerical stellar evolution models now include effects of rotation and binary interaction, while our standard stellar atmosphere codes routinely treat spectral formation in non-LTE, spherical geometry, and under the influence of blanketing due to millions of spectral lines. From an observational perspective, dedicated surveys such as the VLT/FLAMES Tarantula survey have provided key observational diagnostics, while large scale surveys such as GAIA will soon provide precise distances to thousands of massive stars. Current transient surveys such as the Palomar Transient Factory have been providing new information about short-lived phases of massive star evolution and the diverse outcomes of stellar death.

Single-star evolution models have traditionally been verified with comparison to observed statistical populations of massive stars, but those populations are strongly “contaminated" by products of binary evolution. Stellar winds, eruptions and binary mass transfer are proposed as mechanisms to remove a star’s hydrogen envelope, while rapid rotation has been proposed to have a strong influence on both single and binary star evolution. Combining the many parameters of binary evolution with the uncertainty in mass loss recipes and rotation makes this a very difficult problem, since their effects are intertwined and often degenerate. Our proposed FM will take place in a time when the community will have access to numerous results from large observational efforts. Their interpretation and modeling are essential for understanding the physics of massive stars, their eventual fates, and their role as cosmic engines.

In view of the recent progresses and outstanding scientific challenges in massive star evolution, and their significant impacts in many fields of Astrophysics, we propose the Focus Meeting "Massive star evolution in the era of big surveys" during the 2018 IAU General Assembly. Our goal is to bring together colleagues with both theoretical and observational backgrounds to discuss limitations and degeneracies of models and observations, the current and next generation of surveys, and what is needed from both sides to improve our knowledge about how stars evolve. Our proposed FM also aims at discussing with the community about the possibility of establishing “benchmarks” in stellar evolution, which can guide both single and binary stellar evolution models. Examples might be well-constrained nearby massive stars with masses and several other fundamental physical parameters measured in binary systems (including wide binary systems that have not interacted yet as well as those that are likely to be the end product of mass transfer), well-studied evolved stars in clusters with constrained ages, stars at various evolutionary stages with the best possible estimates of mass-loss rates, stars with fundamental physical parameters measured directly through interferometry, constraints from asteroseismology, individual stars that present specific physical mysteries, etc. One could envision establishing a set of benchmark systems that all stellar evolution models should be able to reproduce, in order to reduce free parameters.

We envision that this FM would be of interest not only for a large fraction of our community, but also to researchers active in related fields such as stellar atmospheres, asteroseismology, star formation, supernovae/transients and stellar populations in the near and far Universe. It offers a great chance to identify/clarify/solve outstanding issues, improve the interplay between theoretical and observational studies, and hopefully kickstart collaborative projects that could lead to key progress in massive star evolution.

This LoI has been coordinated with Division G and the IAU Commission G2 "Massive Stars". We will select a gender- and geographically-balanced SOC with members from the massive star, stellar evolution, and stellar atmosphere communities.