Mapping the Stars: A Catalog of Over 50 Million Stars from SMSS and Gaia
Understanding the stars in our galaxy is crucial for uncovering the history of the Milky Way. A new study by Yang Huang and Timothy C. Beers presents a catalog of stellar parameters for over fifty million stars, using data from two massive sky surveys: the SkyMapper Southern Survey (SMSS) Data Release 4 (DR4) and Gaia Data Release 3 (DR3). This updated catalog expands our knowledge of stellar properties like temperature, luminosity classification, and metallicity, making it one of the most extensive collections of its kind.
Expanding the Stellar Database
The authors build on previous work that combined data from different astronomical surveys to estimate stellar metallicities—how much of a star’s composition is made up of elements heavier than hydrogen and helium. Metallicity is important because it helps astronomers classify stars and determine their ages. SMSS DR4 provides improved sky coverage and better data than earlier releases, while Gaia DR3 supplies precise measurements of stellar positions and motions. By applying advanced techniques from earlier studies, the researchers were able to extract reliable stellar parameters for a much larger sample of stars.
Selecting the Best Stars
The study focused on stars with high-quality photometric data—meaning their brightness was measured accurately in specific filters. To ensure reliable results, the authors applied strict selection criteria, filtering out stars with poor-quality data. After this selection process, over 85 million stars were left, most of which had corresponding data in Gaia DR3. To correct for distortions caused by interstellar dust, they used maps that account for how light is scattered and absorbed as it travels through space.
A Catalog of Stellar Properties
Using their refined dataset, the authors determined metallicities for nearly 39 million dwarf stars and 13 million giant stars. They found that their metallicity estimates closely matched those from high-resolution spectroscopic surveys, which directly measure the chemical compositions of stars. However, the study noted some challenges: stars with high amounts of carbon tended to have overestimated metallicities. This issue can be improved by using more specialized filters that are sensitive to carbon.
In addition to metallicity, the researchers calculated other important properties like effective temperature (how hot a star appears), distances for stars too far for direct Gaia measurements, and ages for those with reliable parallax data. This information allows scientists to better understand the different populations of stars in the Milky Way and their evolution over time.
A Race to Catalog the Stars
This work is part of a larger effort called SPORTS (Stellar Parameters fOR all The Stars), a project aimed at determining stellar properties for as many stars as possible using data from ongoing and future astronomical surveys. The full dataset from SMSS DR4 will soon be made available for researchers worldwide, contributing to studies of galactic structure, stellar evolution, and the search for ancient metal-poor stars that provide clues about the early universe.
By assembling this vast collection of stellar parameters, Huang and Beers have taken a significant step forward in mapping the stars of the Milky Way. Their work will provide a valuable resource for astronomers seeking to uncover the history of our galaxy, one star at a time.
Source: Huang
