A team of researchers published recently a new sample catalogue of over 24 million stars that potentially can be used to decode the chemical history of the elements in the Milky Way Galaxy. The researchers from the University of Notre Dame, with the help of collaborators in China and Australia, published the new sample catalogue.
Of the approximately 240 billion stars present in the Milky Way, the sample catalogue represents around one-hundredth of a per cent of the stars. It is a breakthrough for Timothy Beers, the Grace-Rupley Professor of Physics at Notre Dame. The professor has spent most of his career planning and implementing ever-growing surveys of stars to decode how the galaxy was formed and what has been the chemical evolution, which is a field of Astronomy called Galactic Archaeology. To figure out the availability of heavy metals in Milky Way such as iron present in the stars, the researchers used a new method to measure the energy and wavelengths of the light from each star, along with their distances, motions and ages.
The elements present in individual stars can be mapped to trace the chemical embellishment of the Milky Way galaxy, from the time it first began to form stars shortly after the Big Bang to the present day, Beers said.
Beers further said that merging this information with the stellar distances and motions helps to constrain the origin of different elements in the galaxy. When the estimated age is combined, it acts like a `clock’ on the process, which the help of which a more complete picture of the entire process can be drawn.
Spectroscopic work previously undertaken by Beers and the collaborators supplied the information for the tens of thousands of stars that were used to calibrate the new method, which was based on precision photometric measurements. The recent research made use of photometric samples obtained from the Australian SkyMapper Southern Survey and the European Gaia satellite mission to calibrate estimates of metallicity.
Heavy Metals in Milky Way
Till now, the only means to obtain precise estimates of the content of heavy metals for large numbers of stars was through low- resolution and medium-resolution spectra that could be analyzed to draw out the information which was a very long and painstaking process.
Beers is particularly interested in the stars with the lowest metallicities, as they were born in the early phases of the universe, and therefore can convey the origin of elements in the periodic table. In the early 1980s, researchers knew of only around 20 stars that were very metal-poor. However, the new catalogue has pushed up the number to more than 500,000.
The new catalogue has more than nineteen million dwarf stars and around five million giant stars and can help to advance the knowledge of how the Milky Way was formed. This includes specifying the structure of the galactic thin or thick disks, which are the structural components of spiral galaxies, as well as that of the population of stars and globular clusters that surround most of the disk galaxies, known as the stellar halo. The new catalogue of stars will support the researchers in recognizing the arrays of stars left behind from deranged dwarf galaxies and globular clusters.
Journal Reference: Yang Huang, Timothy C. Beers, Christian Wolf, Young Sun Lee, Christopher A. Onken, Haibo Yuan, Derek Shank, Huawei Zhang, Chun Wang, Jianrong Shi, Zhou Fan. Beyond Spectroscopy. I. Metallicities, Distances, and Age Estimates for Over 20 Million Stars from SMSS DR2 and Gaia EDR3. The Astrophysical Journal, 2022; 925 (2): 164 DOI: 10.3847/1538-4357/ac21cb
