Indian Astronomers Link Helium and Lithium Abundance in Ageing Stars
Researchers from the Indian Institute of Astrophysics investigated chemical abundances in ageing stars, primarily red giants, using the Himalayan Chandra Telescope and international data. They developed an indirect method to measure helium, revealing that helium-rich red giants were also unexpectedly rich in lithium. This groundbreaking study, published in The Astrophysical Journal, marks the first time photospheric helium abundance has been correlated with lithium enrichment in these stars, indicating a concurrent enrichment process during stellar evolution.
Indian astronomers from the Indian Institute of Astrophysics (IIA) have conducted a significant study into the chemical abundances of ageing stars, specifically focusing on red giants. The research utilized observations from the ground-based Himalayan Chandra Telescope in Hanle, Ladakh, alongside archival data from telescopes located in Chile, France, and the USA. A key challenge was the direct measurement of helium abundance in cooler stars like our Sun, which do not excite helium enough for observable spectral lines. To overcome this, the astronomers devised a complex indirect method: first observing magnesium's atomic and molecular spectral lines, then using this to determine hydrogen abundance. Given the relative abundance of hydrogen and helium, a reduction in hydrogen indicated an enhancement of helium.The study led to an unexpected discovery: red giant stars found to be rich in helium were also significantly rich in lithium. This is the first time photospheric helium abundance in both normal and lithium-rich red giants has been studied, revealing that lithium enrichment often accompanies helium enrichment in these stellar evolution phases. Lead author BP Hema noted that the method was applied to a sample of 18 red giant stars and 2 super giant stars using high-resolution spectra. Co-author Gajendra Pandey highlighted the key finding: all helium-enhanced red giants were super-lithium rich, although not all lithium-rich giants were helium-enhanced. This suggests that photospheric helium enrichment is indeed accompanied by lithium enrichment in giants, validating their hypothesis. The findings were published in The Astrophysical Journal.
