IIA Study Links Lithium-Rich Red Giant Stars to Enhanced Helium Abundance

A recent study conducted by astronomers at the Indian Institute of Astrophysics (IIA) reveals a correlation between Lithium-rich red giant stars and their enhanced Helium abundance. By analyzing data from the Himalayan Chandra Telescope and other archival sources, the IIA team has gained valuable insights into the evolution of cool giant stars during the red giant phase. Helium, the second most abundant element after hydrogen, plays a vital role in accurately measuring the abundances of other key elements in stars, as well as understanding their structure and evolutionary history.
The measurement of helium abundance in stars is typically done through indirect methods, as it is not directly observable from the star’s surface. This is especially true for cool stars like the Sun and other giant stars with lower temperatures, where helium spectral lines are not easily produced due to insufficient excitation. Therefore, astronomers infer helium abundance by examining its impact on a star’s structure, evolution, and the presence of other observable elements and molecules.
According to the Department of Science and Technology, changes in hydrogen and helium abundances are relative, with an increase in helium proportionate to a decrease in hydrogen levels. In their study, researchers focused on determining hydrogen abundance deviations from standard values by comparing magnesium abundances derived from atomic and molecular spectral lines. By using model atmospheres with varying hydrogen to helium ratios, the team translated these hydrogen deviations into corresponding helium abundances.
This methodology has been successfully applied by the team in previous research, including the determination of the Sun’s Helium abundance. To explore the correlation between lithium and helium abundances, the researchers analyzed a sample of 18 red giant stars and two super giants. Utilizing high-resolution spectra primarily from the Himalayan Chandra Telescope in Hanle, Ladakh, as well as data from various telescopic archives worldwide, the team calculated the effective temperature, surface gravity, and the abundances of 23 different elements.
Among the 20 stars studied, six exhibited higher helium-to-hydrogen ratios than the standard value of 0.1, indicating an enhancement in helium levels. Five of these stars were red giants, while one was a super-giant. The analysis, conducted through the examination of atomic lines and molecular bands using models with appropriate He/H ratios, consistently returned similar magnesium abundances from both MgH and Mg I lines.