(ORDO NEWS) — Giant stars rich in alpha elements, which, according to the theory, should have a small age, were considered by scientists as an anomalous population, since their observed properties do not fit into the theoretical picture of the chemical evolution of the Galaxy.
A new study led by a team led by Zhang Meng of Peking University, China, reveals the nature of these stellar anomalies.
Recent observations have revealed a population of giant alpha-enriched stars that have unexpectedly large masses. If we assume that the star evolved alone, then a large mass indicates its young age.
However, in the context of the chemical evolution of the Galaxy, stars formed in early epochs are usually enriched in alpha elements. Therefore, alpha-rich stars are generally considered ancient.
Several scenarios have been proposed to explain the origin of these alpha-enriched “young” stars. Some of these scenarios involve special conditions for the chemical evolution of stars in certain parts of the galaxy; other scenarios involve evolution as part of binary systems.
In this new study, astronomers studied more than 1,000 alpha-rich “young” stars. As a result of the study, it was found that the chemical composition of these “young” stars differed from the chemical composition of ancient stars enriched in alpha elements.
The “young” stars had more carbon and nitrogen, and the barium abundance was significantly higher for about 15 percent of these stars, compared to most “old” stars. These abundances of elements could not be explained by a single evolution of the star, so astronomers began looking for external sources of this additional abundance of elements.
Considering that barium is mainly produced by deeply evolved stars of the asymptotic giant branch, the authors of the paper proposed these stars as material donors. Thus, “young” alpha-enriched stars pull material rich in carbon and barium from a companion star that lies on the asymptotic giant branch, which forms a binary system with them, Meng and his team found.
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