Letters of Intent received in 2016

LoI 2018-1909
Focus Meeting (GA): Massive stars and low metallicity environments

Topics

- Massive stars in low-metallicity galaxies: evolution and winds
- Interplay with host galaxies: census and gas content
- Very massive stars: the role of environment
- The connection to the intermediate/high redshift Universe: SNe and GRBs
- Roadmap towards the physics of the First Stars

Rationale

Massive stars are cosmic drivers and probes of the Universe in all its ages. In life they are mighty sources of ionizing radiation and mechanical energy. In death they are progenitors of supernovae and long gamma-ray bursts, detected in distant galaxies and promising potential probes of star formation up to high redshift. Understanding the lifecycle of massive stars thus lies at the core of a wide variety of topics in Astrophysics.

In a Universe ever growing in metallicity, any description of massive stars aiming to be comprehensive must assess the role of chemical composition. In particular, metal-poor massive stars hold the key to interpret the intermediate- and high-redshift Universe, and the connection to the pristine First Stars. While solar-like metallicity massive stars are readily accessible in the Milky Way, enabling large and homogeneous studies, the low-metallicity end remains insufficiently characterized. For years, the SMC has been the standard for the low-metallicity regime, serving as test-bed for the physics of metal-poor massive stars and feeding population synthesis codes with spectral libraries. However, with a global metallicity 1/5 solar, these environmental conditions are far from the 1/300 solar detected in z=5 quasars and the roughly metal-free infant Universe.

Multi-object spectrographs on 8-10m ground-based telescopes, and the COS UV spectrograph on-board HST, broke the distance and metallicity frontier set by the SMC. In the past 10 years they have enabled the first quantitative analysis of massive stars with ~1/10 solar in dwarf irregular galaxies of the Local Group and outer reaches. However, the samples of stars and quantitative studies are still small and numerous questions still remain:
- Is the physics of low-metallicity massive stars significantly different from the solar-like analogs?
- What is the mass lost to radiation driven winds? Does it significantly impact the life of the star?
- Do we understand their evolutionary pathways? What percentage undergo chemically homogeneous evolution?
- Can single-star evolution reproduce the observed rates of SNe and GRBs? What is the binary fraction in metal-poor populations?
- Is there observational evidence supporting that more massive stars can be produced in pristine clouds? If so, why very massive stars have only been found in 30 Doradus?
- What is the role of environment then, and does it challenge the paradigm for the formation and physics of the First Stars of the Universe?

The field is about to experience a new boost with the second generation of high-multiplexing optical spectrographs (MUSE, MEGARA), plus the prospect of the E-ELT in the intermediate future. These instruments will yield the integral characterization of the population of massive stars in metal-poor Local Group galaxies, explore other promising groups, and finally tackle the next milestone in the road to the metal-free stars: IZw18.

The goal of this focus meeting is to bring together current evidence and models for resolved massive stars with sub-SMC metallicity, and get ready for the upcoming instrumentation. The meeting will have an inter-disciplinary component, targeting the SN/GRB and starburst community and including invited talks on their latest results. A further topic for discussion will be the interplay between massive stars and their host galaxies (e.g. the consequences of gas content and low metallicities on both the formation of massive stars and their subsequent feedback in terms of ionizing photons and mass-loss).