Letters of Intent for 2015

LoI 2015-183
Focus Meeting: Stellar Behemoths - Red Supergiants Across the Local Universe


10 August 2015 to 12 August 2015


Hawaii, United Kingdom


Ben Davies (

Coordinating division:

Division G Stars and Stellar Physics

Chair of SOC:

Ben Davies (Liverpool John Moores University)

Chair of LOC:

n/a ()



* The physical properties of RSGs
Even the most basic stellar parameters, such as temperature, luminosity and radius, are still not definitively known. What do the latest observations tell us? How do these compare to the predictions of stellar models?

* The structure and atmospheres of RSGs
How well can we model their atmospheres, such that we can we interpret their spectra? What is the status of 3-D hydrodynamical models of convective stars? What testable predictions do these models make, and how do they compare to observations?

* Evolutionary connections
Which stars become RSGs? What keeps them in the red part of the HR diagram? What effect do factors such as binarity/metallicity/mass-loss have? What connection can we make to their evolutionary neighbours, e.g. yellow and blue supergiants?

* Mass-loss from RSGs
How is material ejected from these stars? How can we measure their mass-loss rates? How do their winds evolve with time? How does this impact on their evolution?

* RSGs as supernova progenitors
What are the properties of those stars identified as direct progenitors? What happens to the brightest RSGs, none of which have yet been seen to explode as SNe?

* RSG populations on galactic scales
What can we learn from RSG-dominated star-clusters? What do RSGs tell us about the structure and star-forming history of their host galaxies?



Red Supergiants (RSGs) are an evolved state of stars with masses greater than 10Msun. They are the largest stars known, with radii up to 1000x larger than the Sun. Their extremely high luminosities peak in the near-infrared, allow us to observe them at distances of over 10Mpc and through many magnitudes of optical extinction. This makes them powerful tools with which to study their host galaxies' structure, chemical evolution and star-formation rate (including the Milky Way). They are also bright enough to have been identified as direct progenitors of distant supernovae, with current sample sizes now becoming large enough such that statistical conclusions about the fate of massive stars can be drawn.

However, they are arguably one of the least well-understood classes of stars, with even their basic properties still being hotly debated. This is largely due to historical reasons: massive star research has tended to focus on hot stars, such as O stars and Wolf-Rayets. The expertise necessary for analysing and modelling RSGs, such as the treatment of convection and molecular opacities, has been developed primarily by the low-mass star community for studying objects such as Solar-type stars and red giants. It is only very recently, when the importance and diagnostic potential of RSGs has been widely recognised, that the two communities have begun to work together.

The next 12 months sees the commissioning of brand-new instrumentation and facilities (e.g. MOSFIRE, KMOS, ALMA, VLTI) which will provide new windows into the nature of these stars. At the 2015 IAU-GA we aim to bring together the leading researchers in the fields of massive stars, cool stars, and supernovae, for a 3 day meeting to discuss these new results.

This meeting has the support of the IAU Division G (Stars and Stellar Physics), Commission 36 (Theory of Stellar Atmospheres), and the Division G WG on Massive Stars. The issues to be discussed at this meeting are also particularly relevant to the following IAU bodies:

Division G Commission 29 Stellar Spectra
Division G Commission 35 Stellar Constitution
Division H Commission 37 Star Clusters & Associations
Division H Commission 33 Structure & Dynamics of the Galactic System
Division VIII WG Supernovae

There are also additional links to:

Division G WG Abundances in Red Giants
Division G Commission 27 Variable Stars
Division J Commission 28 Galaxies
Division B Commission 54 Optical & Infrared Interferometry

This LoI has been coordinated on behalf of the IAU working group on massive stars and followed discussions between Ben Davies, Artemio Herrero, Joachim Puls, and Rolf-Peter Kudritzki. We anticipate the SOC to consist of experts in the fields of massive stars, cool stars, stellar atmospheres, and supernova progenitors.


Office for Astronomy Development

Office for Astronomy Development

Strategic Plan

International Year of Astronomy