Free Astronomy Magazine July-August 2019

48 SPACE CHRONICLES Heavier elements than hydrogen and helium are consid- ered as metals in as- tronomy and their presence deter- mines the metallic- ity of a star. As time passed and stars died, the con- tent of such metals in the Milky Way and in the new stars born increased. Therefore, old stars have lower metallicity than younger ones. “Since old stars can reveal important informa- tion about the structure and the chemical evolution of the Milky Way, it is essential for astronomers to determine their most basic stellar parameters such as masses and radii” , explains the researcher from the UPC and IEEC A n international team, led by a researcher from the Universitat Politècnica de Catalunya - BarcelonaTech (UPC) and the Institute of Space Studies of Cat- alonia (IEEC), has measured for the first time the stellar parameters of a very old kind of stars, known as cool subdwarf stars, in our Galaxy, the Milky Way. Cool subdwarfs are stars like our Sun, but of smaller mass and radius, which formed during the beginning of the Milky Way and, therefore, carry important in- formation about its structure and chemical evolution. The work has been done in collaboration with re- searchers from the University of Sheffield and the National Astro- nomical Observatories, Chinese Academy of Sciences, and the re- sults are published in the journal Nature Astronomy . When the Milky Way formed, the first stars were mainly composed of hydrogen. by IAC HiPERCAM reveals new details about the oldest stars in the Milky Way JULY-AUGUST 2019