Based on data from the Hubble Space Telescope (HST) and from ground-based facilities, we derived high-precision multi-band photometry of ~200 Galactic and extragalactic star clusters that span a wide range of ages and metallicities.
Our analysis comprises all images of Magellanic Cloud clusters collected with the modern cameras of HST and all images of Galactic GCs with UV observations.
We corrected the photometry for differential reddening and calculated proper motions when multi-epoch images are available.
We inspected the catalogs to identify the MPs by using appropriate diagrams that maximize the separation among the distinct populations. These include the pseudo-two-color diagram dubbed 'chromosome map' (ChM), introduced by the PI
We detected MPs in more than 70 GCs older than 2 Gyr and extended main-sequence turn-off (eMSTOs) in all clusters younger than 2Gyr.
The investigation of GCs includes:
- determination of the relative numbers of 1P and 2P stars
- determination of the chemical composition of the stellar population. To do this, we followed complementary approaches i) we combined information from high-resolution spectroscopy and the ChM to derive detailed abundances in 30 GCs ii) we adopted a technique introduced by our team based on the synergy of multi-band photometry, synthetic spectra, and stellar models to infer the abundances of He, C, N, O, Mg of MPs of all GCs (Milone et al. 2018a, 2020a,b; Lagioia et al. 2019a,b).
- Results on chemical composition allowed us to infer the amount of mass loss and derive a new mass-loss law.
- we developed a new technique, based on observations from HST, ground-based facilities, and the GAIA satellite, to measure the MP kinematics and constrain their spatial distributions (Milone et al. 2018b, Cordoni et al. 2020a,b, Dondoglio et al. 2021).
- we developed new methods to infer the frequency of binaries among the distinct stellar populations.
- we investigated MPs along the main evolutionary stages, from the tip of the red-giant branch to the upper main sequence (MS). We detected MPs among very low-mass stars and inferred their chemical composition and mass functions.
- we investigate the relations between the properties of the MPs, the main cluster parameters, the host galaxy, and the environment.
Our project comprises the study of more than 100 young clusters. Results include:
- we identified MPs in the photometric diagrams. We discovered that split MSs are present in all clusters younger than 800 Myr, whereas eMSTOs are common features in clusters younger than 2 Gyr.
- We provide direct evidence, by means of both photometry and high-resolution spectroscopy, that the split MS corresponds to stellar populations with different rotation rates (Milone et al. 2018c, Cordoni et al. 2018, Marino, Milone, et al. 2018a,b).
- We investigate the properties of MPs in young clusters and explored the relations with the stellar mass and the properties of the host cluster.
Results on stellar populations in young clusters and GCs are compared with each other to understand whether or not the young clusters are the counterparts of GCs with MPs.
