Researchers at the University of Notre Dame have published a new sample catalog of more than 24 million stars that may be used to analyze the chemical history of elements in the Milky Way Galaxy with collaborators from China and Australia.
The study, which was published in The Astrophysical Journal this month (February 2022), represents about one-hundredth of one percent of the Milky Way’s 240 billion stars. It’s a watershed moment for Timothy Beers, the Grace-Rupley Professor of Physics at Notre Dame, who has spent the majority of his career organizing and conducting ever-larger surveys of stars in the subject of galactic archaeology, which studies the birth and chemical development of galaxies.
Researchers used a novel method to calculate the abundance of heavy elements like iron by measuring the light from each star. Their distances, motions, and ages were also recorded.
“The elemental abundances of individual stars trace the chemical enrichment of the Milky Way galaxy, from when it first began to form stars shortly after the Big Bang to the present,” Beers said.
“Combining this information with the stellar distances and motions allows us to constrain the origin of different components in the galaxy, such as the halo and disk populations,” he continued. “Adding age estimates puts a ‘clock’ on the process so that a much more complete picture of the entire process can be drawn.”
Combining this information with the stellar distances and motions allows us to constrain the origin of different components in the galaxy, such as the halo and disk populations. Adding age estimates puts a ‘clock’ on the process, so that a much more complete picture of the entire process can be drawn.
Timothy Beers
Beers and partners’ previous spectroscopic work gave the data for the tens of thousands of stars necessary to calibrate the new approach, which is based on precision photometric measurements.
To calibrate estimates of metallicity, researchers used extensive photometric samples obtained with the Australian SkyMapper Southern Survey and the European Gaia satellite mission.
Until recently, the only way to get precise estimates of the abundance of heavy metals like iron in a large number of stars was to use low and medium-resolution spectra that could be examined to extract this data. It was a lengthy and arduous procedure.
Beers is most interested in the stars with the lowest metallicities, which are highly metal-poor stars with iron abundances less than 1% of the sun, because they formed early in the universe’s history and thus indicate the genesis of elements in the periodic table.
When Beers began his research in the early 1980s, there were only approximately 20 highly metal-poor stars known. This latest catalog takes the total number of “night sky fossils” collected by Beers to over 500,000.
The new catalog, which contains more than 19 million dwarf and five million big stars, is anticipated to increase knowledge of how the Milky Way was generated in a variety of ways, according to Beers.
Characterizing the structure of galaxy thin/thick disks, spiral galaxies’ structural components, and the population of stars and globular clusters that surround most disk galaxies, known as the stellar halo, are among them. The star catalog will also aid astronomers in locating star trails left by broken dwarf galaxies and globular clusters.
In addition to Beers and graduate student Derek Shank at the University of Notre Dame, other collaborators include lead author Yang Huang of Yunnan University, China; Christian Wolf and Christopher A. Onken, Australian National University; Young Sun Lee, Chungnam National University, Korea; Haibo Yuan, Beijing Normal University, China; Huawei Zhang, Peking University, China; Chun Wang, Tianjin Normal University, China; and Jianrong Shi and Zhou Fan, Chinese Academy of Sciences.
Beers and Shank’s work on this project received support from grant 14-30152, Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the U.S. National Science Foundation. Beers also received support from a 2019 PIFI Distinguished Scientist award from the Chinese Academy of Science.
