DivG: Stars and Stellar Physics – a Science Revolution in Progress

The violent youth of solar proxies

Stars similar to our Sun — “solar proxies” — enable scientists to look through a window in time to see the harsh conditions prevailing in the early or future Solar System, as well as in planetary systems around other stars. (IAU/E. Guinan)

Stars are fundamental bricks of the baryonic Universe. They produce energy, radiation and chemical elements that shape the structures of the Universe from small to very large scales in both space and time. Understanding how they form, evolve, die and interact with their environments is a fundamental challenge. The lives of stars have deep implications for the proper description of the assembly and the evolution of exoplanetary systems, of galaxies over cosmic time and of the Universe as a whole. This requires multi-disciplinary developments in cosmology and fundamental physics, including nuclear and particle physics.

Stellar astrophysics is in the middle of a revolution driven by the large amount of detailed data being gathered via with new multi-messenger techniques. Resulting high-resolution spectroscopic and photometric surveys, coupled to ultra-high precision astrometry, are providing chrono-chemo-kinematical information on stellar populations in the Milky Way and beyond. The maturing field of asteroseismology further brings information on stellar interiors together with constraints on fundamental stellar parameters and evolutionary clocks. These techniques are independent of the classical methods, such as studying very large samples of stars over the entire Hertzsprung-Russell diagram. Interferometry and adaptive optics further reveal details of stellar surfaces that previously were only seen on the Sun. Spectropolarimetric observations coupled with tomographic techniques also reveal the large-scale magnetic topologies of stars. Finally, the recent detection of gravitational waves brings a new means to study stars and their remnants using observational clues beyond the electromagnetic spectrum. The coming decade will see a vast proliferation of these techniques, thanks to the advent of extremely large telescopes and of dedicated instruments and space missions.

Magnetohydrodynamical processes, as typically manifested through convection, mixing, rotation, magnetic activity, winds, interactions in multiple systems and interplay with interstellar surroundings, remains the largest uncertainty in modern stellar astrophysics. The crucial implications of this area of study range from cosmic re-ionisation and distance ladders to galactic evolution and exoplanet habitability. The growth of computational resources to simulate stellar magnetohydrodynamics, from the formation of stars to the explosions of supernovae, holds promise for substantial improvements in the next decade, in synergy with astrostatistics and big data science.

The role of Division G

Division G is committed to fostering research on stars and stellar physics, to the distribution of key stellar data and model predictions to the research community on astrophysics, as well as to providing a forum for the exchange of ideas. Our activities focus on understanding the properties of stars of all masses and evolutionary stages, and the physical mechanisms that govern them. This covers a broad range of aspects, including the determination of stellar observable properties and their time variability, the investigation of their atmospheric and internal constitution, as well as the theoretical modelling of stellar formation, structure, and evolution. These efforts include the techniques used to measure and classify stars such as spectroscopy, radial velocities and photometry, and the production of stellar predictions (e.g. stellar evolution tracks, lifetimes, chemical yields, star-planet interactions, etc). Division G is also concerned with stellar binarity and multiplicity, from close to wide systems.

Division G organisation – Commissions, Working Groups, and Steering Committee

Division G is the parent division of five Commissions and two Inter-Division Commissions:

Divison G also has 4 Working Groups:

During the term 2015-2018, 3081 IAU members were affiliated with Division G. The Steering Committee was composed of David Soderblom (Vice-President), Tabetha Boyajian (Secretary), Artemio Herrero (Commission G2 President), Ivan Hubeny (Commission G5 President), Simon Jeffery (Commission G4 President), John C. Lattanzio (Commission G3 President), Andrej Prša (Commission G1 President), Ignasi Ribas (Advisor – Past President), Martin Asplund, Francesca D’Antona, Pierre Kervella, Geraldine Peters, Virginia Trimble, and myself (President). I wish to thank them all sincerely for their great work, combined efforts, and clever advises during the triennium.

We are now passing the torch on to the new Steering Committee: David Soderblom (President), Andrej Prša (Vice-President), elected members Merieme Chadid and Heidi Korhonen, second term members Tabetha Boyajian, Geraldine Peter and Pierre Kervella and ex-officio members Virginia Trimble (Commission G1 President), Jorick Vink (Commission G2 President), Marc Pinsonneault (Commission G3 President), Jaymie Matthews (Commission G4 President), and Carlos Allende Prieto (Commission G5 President). I look forward to remaining in the Steering Committee as advisor.

Division G achievements – PhD prizes and Symposia

The Steering Committees two major yearly tasks are reviewing proposals for IAU symposia and applications for the IAU PhD Prize. Over the past two years, Division G received a total of 23 applications for these new PhD prizes (first awarded in 2016), and judged most of them to be excellent, making selection particularly hard. The first two prizes were awarded to Morgan MacLeod (University of California Santa Cruz, USA, PhD Prize 2016) for his work entitled “Social Stars: Modeling the Interactive Lives of Stars in Dense Clusters and Binary Systems in the Era of Time Domain Astronomy”, and to Gaël Buldgen (University of Liège, Belgium, PhD Prize 2017) for his work on “Development of inversion techniques in Asteroseismology”. We congratulate Morgan and Gaël, who will be presenting their work during the Division Days in Vienna. We also congratulate all the other applicants for excellent science relevant to Division G.

Division Days in Vienna

On Friday, August 24th, Division G holds the mini-symposium “Stars and Stellar Physics – The asteroseismic revolution”. We kindly invite you to attend this event and to learn more about new results from asteroseismology and the insights into stellar structure and evolution they have provided. Over the past decade, asteroseismology has blossomed because facilities like Corot and Kepler have detected stellar oscillations as subtle as the Sun’s, and future missions promise even more such detections. We can now observe stellar oscillations for stars across most of the Hertzsprung-Russell diagram.

On Monday, August 27, Division G holds its business meeting during the morning session and the afternoon will be dedicated to scientific presentations on a variety of subjects. Everyone interested in Stars and Stellar Physics is welcome.

Corinne CharbonnelCorinne Charbonnel, Professor at the University of Geneva, Switzerland, and Senior Researcher at CNRS, France, President of IAU Division G Stars and Stellar Physics (2015-2018), former president of the French Society of Astronomy and Astrophysics (SF2A, 2010-2012). (The author originally wrote part of this text for IAU strategic plan 2020-2030)