Global-assembly · Building up the Milky Way Halo in the era of multiple stellar populations

Building up the Milky Way Halo in the era of multiple stellar populations

"This project aims to advance our knowledge of the most ancient stellar systems in the Milky Way, the globular clusters (GCs). The study of the newly discovered generations of stars in GCs is an active branch of stellar and Galactic astrophysics. Global-assembly investigates this phenomenon, to address some of the fundamental issues: What is the nature of the first stars? How do galaxies evolve across cosmic time? How are elements produced by stars, recycled through galaxies, eventually producing the elements for life itself? The outcome of this research will help us to advance in a vast range of fields, from cosmology to stellar physics, i.e.the contribution of GCs to the Galactic Halo, star formation in dense ancient stellar systems, the role of GCs to the cosmic reionization. Understanding the origin of stellar populations in GCs is a necessary step to constrain stellar evolution and nucleosynthesis, i.e. the production of the chemical elements in stars, then recycled into galaxies, and eventually producing the matter for life itself. The objective is a detailed analysis of the multiple populations in star clusters to shed light on their origin. This analysis includes: 1) The chemical tagging of all the sub-populations observed through the “chromosome maps”, a photometric diagram which is a powerful population diagnostic unique to each GC; 2) The investigation of possible chemical variations in first population stars, crucial to constrain the GCs’ mass-loss into the field; 3) A survey of the anomalous GCs, i.e. GCs with a complex star-formation, which might be associated with former dwarf galaxies; 4) The construction of grids of synthetic spectra with the chemical composition typical of the different populations, useful for various purposes, like the determination of He variations in a given GC, and for the construction of more realistic isochrone databases; 5) Multiple populations in young clusters in the Magellanic Clouds to understand if they are the counterpart of old Milky Way GCs; 6) Kinematics of different populations combining radial velocities from spectroscopy and proper motions from Gaia. Global-assembly has exploited chromosome maps to study the elemental abundances characterizing each stellar population, providing the first and most complete “chemical key"" to read these maps. It has been shown that the GCs with specific morphological features on the map, have an “anomalous” chemical composition with internal variations in iron. The project has provided evidence for chemical variations in the overall metallicity among stars associated with the main first populations. Small internal variations in helium have been found in younger clusters, with age of ~6-11 Gyr. The analysis of kinematic properties has shown for the first time a distinct overall rotation of different stellar populations in a GC."

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз