Resolved stellar populations

Since the first use of the term “stellar population” by Baade in 1944, this concept has evolved, was refined, and allowed us to go a long way in the study of the Milky Way and the Local Group of galaxies, but also of stellar astrophysics. Over half a century, accurate stellar photometry and spectroscopy, as invaluable investigation techniques, have allowed us to study stellar populations in great detail. More recently, the advent of large surveys and space missions facilitates a robust characterization of the collective properties of stellar populations, while also allowing the discovery of rare objects. Thanks to his interest in science and his special skills for computational techniques, Peter B. Stetson has been leading some of the greatest discoveries of the past 40 years, while also enabling a large fraction of the others, made by other people using his software and data. The stellar populations studied by him and his collaborators include the main components of the Milky Way, disks, bulge, and halo; both open and globular clusters; dwarf galaxies, and the streams of stars left by disrupting Galactic satellites.  

Within all these topics, Peter’s touch has been to ensure extracting the most accurate information from the data, and to homogenize data processing in such a way to be able to perform meaningful comparison across different studies. Those of us who had the fortune to work with him appreciate this as a legacy of his own and do our best to preserve and pass it on to the younger generations. In addition to a celebration of his career, this Conference will help us spread Peter’s heritage. 

In terms of methods, Peter is one of the fathers of modern photometry. His DAOPHOT code was developed in the pioneering era of CCD photometry. It is still used by a large community after more than 30 years, producing new and exciting discoveries, and it is one bright example of the contribution he made to the advancement of knowledge in the field. In terms of data, he is presently working on the largest existing database of homogeneously and accurately calibrated photometric data and secondary Johnson-Kron-Cousins standard stars. The database is based on more than a million proprietary and public images and some objects have been observed thousands of times, representing an invaluable source of information on stellar variability, complementary to large projects like the Vera Rubin Observatory.