Stellar Populations

Stellar Populations


G. Piotto, G. Carraro, S. Ortolani


M. Libralato, M. Montalto, D. Nardiello

PhD student

M. Simioni

Globular Clusters (GCs)

The GCs are the oldest objects in the universe for which we can give a precise estimate of the age and obtain fundamental information on the conditions of the primordial universe. In the past, it was believed they are composed by simple stellar populations, i.e., stars with the same chemical composition, formed in a short temporal interval. Our group, thanks to the intense use of HST, has shown that these objects contain many distinct stellar populations, characterized by different light elements content (C, N, O, Na, Mg, Al), including He. The presence of multiple stellar populations has revolutionized this research field and it may be the proof of still-misunderstood conditions of star formation in the primordial universe.

Our group is a world leader in this field (more than 250 publications on peer review journals, with more than 15,000 citations), thanks to the tremendous effort in the software development in order to obtain high-precision photometric and astrometric measurements with HST data. The same software was then adapted to obtain high-precision photometry and astrometry with images taken with ground-based telescopes.

We are currently involved in different photometric and spectroscopic observational campaigns with space-based instruments, including a HST UV Legacy Treasury project, and ground-based telescopes, e.g., VLT and LBT. The main goals are to map the multiple populations hosted in different clusters, chemically characterize them, study their spatial distribution and kinematics, within the cluster and in the possible tidal tails.

We have recently extended the study and characterization of multiple stellar populations in Galactic GCs to near-infrared wavelengths and we are preparing an observational campaign with the James Webb Space Telescope.

Furthermore, the study of multiple stellar populations in the Magellanic Clouds is already underway.

We are part of a large international collaboration for the photometric, astrometric and spectroscopic study of the GCs in the Galactic bulge. We use Bulge clusters as age and chemical-composition tracers to comprehend the Bulge formation and understand whether the Bulge was formed at the same time or even before the Halo.

Open clusters (OCs)

We are carrying out spectroscopic observations of blue-straggler candidates in some OCs, with different ages, in order to understand how they formed.

Thanks to the spectroscopic observations of a selected sample of OCs, we are currently studying the Orion arm in the Galaxy, to clarify its nature and formation mechanism.

We are also involved in the Gaia-ESO observing campaign, which is collecting high-resolution spectra of more than 100,000 stars in the Galaxy in order to obtain the first all-scale distribution of chemical-element abundances of the Milky Way.

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