Starting from the middle 90's, FRF is coordinator of several projects on stellar astrophysics at the Bologna Astronomical Observatory first and from 2002 at the University of Bologna. His main research subjects can be schematically listed as follows: (1) the design and application of observational tests to validate the stellar evolution theory; (2) the observational study of resolved stellar populations in globular clusters in the context of the deepest understanding of the galaxy formation processes in the Universe; (3) the study of the effect of the stellar cluster dynamical evolution on the "passive" evolution of stars and binary systems.
In this context FRF is PI of a number of scientific projects aimed at the study of stellar populations in high-density star clusters with the specific aim of understanding their formation mechanisms, their structure and dynamical evolution, with the final goal of extracting precious information on the formation and evolution of our galaxy and (in general) on the assembling process of galaxies in the Universe. This research involves a large number of international scientists and it is carried out by exploiting the powerful combination of large high-resolution photometric and multi-instrument spectroscopic data-sets (acquired at the largest ground-based telescopes and from the space) with state-of-art dynamical models and N-body simulations.
The results of his PhD Thesis (published in Fusi Pecci, Ferraro et al. 1990, A&A 238, 95) allowed the first systematic identification of the so-called “RGB bump” in a sample of GCs. This work triggered a systematic approach to the photometric characterization of the main evolutionary sequences in the Color Magnitude Diagram of GCs (see Ferraro et al 1999, AJ, 118, 1738 and Ferraro et al. 2000, AJ 119, 1282). From the point of view of both the methodology and the observational approach, these works are considered two masterpieces in the field of empirically checking the predictions of the stellar evolution theory and they have triggered new generations of theoretical models.
FRF is among the pioneers of the multi-wavelength and multi-technique approach to the study of Stellar Populations (SPs) by exploiting the very first generation of infrared and ultraviolet detectors. A few example are:
- The IR approach to the study of giants in GCs - Ferraro et al. 1994, MNRAS 266, 829; Ferraro et al. 1995, MNRAS 272, 391; Ferraro et al. 2000, AJ 119, 1282; Ferraro et al. 2004, ApJ, 608, 772.
- The UV route to the study of hot stellar populations in clusters- Ferraro & Paresce 1993, AJ 106, 154; Ferraro et al. 1997, ApJ 484, L145; Ferraro et al. 2001, ApJ 561, 337; Ferraro et al., 2003, ApJ, 588, 464. These seminal works have inspired tens of subsequent observational investigations.
Over the years, FRF demonstrated the capacity of single out the most suited approach for solving a given problem, promptly recognizing the effectiveness and the advantages of a synergic use of the most advanced instrumentation and facilities available to the international astronomical community. In the following a short list of major achievements:
- The first direct evidence of the RGB-phase transition in SPs: Ferraro et al. (1995, MNRAS 272, 391); Ferraro et al. (2004, ApJ 608, 772).
- The empirical calibration of the mixing length parameter: Ferraro et al. (2006, ApJ 642, 225).
- The first clear-cut evidence of multi-populations along the HB in GCs: Ferraro et al. (1998, ApJ 500, 311).
- The discovery of the anomalous SGB in Omega Centauri: Ferraro et al. 2004, ApJ 603, L81.
- The discovery of a fossil remnant of the Bulge formation process (Ferraro et al 2009, Nature, 462, 483)
- The stellar system Terzan 5:Linking the Galactic Bulge to the High-z Universe (Ferraro et al. 2016, ApJ, 828, 75)
- The Multi-instrument Kinematic Survey of Galactic Globular Clusters (Ferraro et al. 2018, ApJ, 860, 50)
FRF proposed innovative concepts now generally accepted, as the idea that the environment can significantly alter the passive evolution of stars and that the dynamical age of star clusters can be measured from the blue straggler (BSS) radial distribution. These concepts have been settled by means of a series of seminal discoveries:
- The discovery of the first BSS bimodal radial distribution (Ferraro et al.1997, A&A, 324,915)
- The discovery of the first dynamically unevolved BSS distribution (Ferraro et al., 2006, ApJ, 638, 433)
- The discovery of chemical anomalies tracing the BSS formation process (Ferraro et al., 2006, 647, L53)
- The first discovery of two distinct sequences of Blue Straggler Stars in a GC (Ferraro et al 2009, Nature, 462, 1028)
- The definition of an empirical clock able to measure the dynamical age of stellar system (the so-called “dynamical clock”): Ferraro et al. 2012, Nature, 492, 393.
- The definition of an empirical "stellar scale" able to pinpoint anomalous heavy objects among photometrically indistinguishable stars (Ferraro et al., 2016, ApJ, 816,70).
- The empirical measure of the dynamical age of 48 GCs (Ferraro et al., 2018, ApJ, 860, 36).
FRF by means of a few seminal papers has promoted the systematic search for the optical companion to binary Millisecond pulsar (MSP) in GCs. This project has been extremely successful since at the moment more than 50% of the known optical counterparts to MSP in GCs have been discovered by his group:
- The first discovery of a newborn MSP in NGC6397 (Ferraro et al. 2001, ApJ 561, L93);
- The most accurate mass ratio for any non relativistic binary system containing a neutron star (Ferraro et al. 2003, ApJ 584, L13).
- The optical companion to the most off-center MSP in GCs (Ferraro et al. (2003, ApJ 596,L211).
- Probing the MSP prenatal-stage (Ferraro et al. 2015, ApJ 807, L1);
FRF has published more than 500 papers, among them, more than 250 on referred journals and several invited reviews. Note that in the last 10 years FRF has published more than 120 refereed papers in the most prestigiuos international astronomical jornals (with the impressive average rate of one published paper per month over 10 years).
The international impact of his scientific production is high, as demonstrated by the 13000 citations in the literature. Many international ESO/ESA/NASA/Keck/Gemini press releases have been dedicated to results of his works. The most recent example is the ESA/Hubble press release https://www.spacetelescope.org/news/heic1617/, related to the paper "The Age of the Young Bulge-like Population in the Stellar System Terzan 5: Linking the Galactic Bulge to the High-z Universe" (Ferraro et al. 2016, ApJ, 828, 75), which proposes an unsuspected connection between Terzan5 and the giant clumps observed in star-forming galaxies at high-redshift, thus providing a new crucial contribution to the debate of how galaxy bulges form.
From May 2011 to April 2016 FRF has led the programme COSMIC-LAB, a project funded by the European Research Council within the FP7 Advanced Grant programme with a grant of about 1.9 milion of Euros.