A new study has traced a link between Lithium-rich red giant stars and their enhanced Helium abundance, using data from the Himalayan Chandra Telescope and other archival data. The study gives a new lead to the evolution of cool giant stars along the red giant phase.
Helium, the most abundant element next to hydrogen, plays a crucial role in measuring the abundances of other key elements accurately, and also to understand the structure and evolutionary history of stars. The helium abundance in stars is measured using indirect methods as it is not directly observable from the star’s surface. Particularly in cool stars, like our Sun and other cooler giants, the surface temperature is not sufficient to excite helium to produce observable spectral lines. Hence, helium abundance is inferred by analyzing the effects on a star’s structure, evolution and other observable elements and molecules.
The change in hydrogen and helium abundance is relative. If there is reduction in hydrogen, helium is enhanced proportionally.
In a study by astronomers at the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology (DST) researchers measured the Hydrogen abundance, and any departure from its standard value, by comparing the magnesium abundances derived from its atomic versus molecular spectral lines.
This departure in hydrogen abundance was then translated to the corresponding helium abundance using the model atmospheres computed for differing values of hydrogen to helium ratio (He/H ratio). This method was also effectively used by the team for determining the Helium abundance of the Sun in an earlier work.