Director Emeritus, George Preston has been deciphering the chemical evolution of stars in our Milky Way for a quarter of a century. He and Steve Shectman started this quest using a special technique to conduct a needle-in-the-haystack search for the few, first-generation stars, whose chemical compositions sketch the history of element formation in the galaxy. These earliest stars are very rare and they are characteristically low in heavy metals because of their age. They were made of Big Bang material, mostly hydrogen and helium. It was only later that heavier elements were formed in the nuclear furnaces of newer stars.
In their first study, Preston and Shectman compiled a list of hundreds of candidate so-called low-metal/old stars. They followed it with a more detailed analysis confirming their status, one by one. Over the years, others joined the effort.
Preston explores the consequences of the very first survey using the facilities at Carnegie’s Las Campanas Observatory. He is tracing the rates of atomic enrichment of different types of atoms produced by various nuclear mechanisms. He uses the decay rate of radioactive thorium in some of the oldest stars to measure their ages. By discovering traces of the heaviest stable elements, lead and bismuth, he is also looking into the processes in other stars to refine theories of special nucleosynthesis—a process that creates and expels elements in certain dying stars. He also explores the mysteries of mass exchange between members of old binary star systems that contain these dying stars.
More recently he has turned his attention to a surprising find—a recently-discovered pulsating (RR Lyrae) star highly enriched in carbon, a characteristic that defies experience and prior expectations.
Preston received his degree in physics from Yale University and his Ph.D. in astronomy from the University of California, Berkeley. He was a Carnegie Fellow with the Mount Wilson Observatory from 1959 to 1960. In 1965 he won the Helen B. Warner Prize for astronomy from the American Astronomical Society. Preston has been a Carnegie staff member since 1968 and served as director of the Observatories from 1981 to 1986. For more information see http://obs.carnegiescience.edu/users/gwp.
