Abundance of lithium in low mass red giants traced to He-flashing phase of 2 million years
The researchers used asteroseismology (seismic study of stars using time-resolved photometry from Kepler space telescope) combined with spectroscopic abundances of elements to track the evolution of lithium in a sample of giant stars
Scientists from the Indian Institute of astrophysics have pinned down the mechanism behind the abundance of Lithium production in low mass red clump stars that has intrigued astronomers the world over for a long time. Having found lithium excess to be common among the low mass red clump giants, they have now traced Helium (He)-flashing phase of the star's evolution as the site for high lithium production. This transition phase lasts for about 2 million, during which RGB giants with inert He-core at the centre become red clump giants of He-core burning, scientists say.
Recently, a group of Astronomers at the Indian Institute of Astrophysics (IIA), Bengaluru, an autonomous institute of the Department of Science & Technology, Government of India, found observational evidence for Li enhancement during the helium-flashing phase of 2 million years, followed by a rapid decrease in Li abundances of such stars. According to their work, it seems Li excess in giants is a transient phenomenon, the Union Science and Technology Ministry said.
The study team was led by Raghubar Singh and Prof. Eswar Reddy of IIA (including Simon Campbell of Monash Univ, Australia, Bharat Kumar of CAS, China, Matheu Vrard of Ohio State Univ. the USA).
The researchers used asteroseismology (seismic study of stars using time-resolved photometry from Kepler space telescope) combined with spectroscopic abundances of elements to track the evolution of lithium in a sample of giant stars.
In addition to the evidence for Li production site, a first-of-its-kind correlation between the two independent observed quantities Li abundance and stellar oscillations (gravity mode period spacing) will serve to track the He-flashing phase of converting RGB giant of an inert, electron-degenerate He-core into a fully convective He-burning core by a series of core He-flashes, a theory developed in the 1960s, the scientists said.
"We do not have much insight into the He-flash phase, let alone understanding of lithium production. These new results will inspire further observations as well as theoretical models," Raghubar Singh said.
Prof Eswar Reddy highlighted the importance of this result:
"These results will be of great interest to a larger community of theoreticians and observers. This is because of lithium's broader implications to cosmological models, which predict Big Bang lithium abundance, which is a factor of four less than the presently observed values in the interstellar medium or very young stars, indicating lithium is increasing. Identification of production sites is important for accounting for Li enhancement in the Universe and provides excellent insights into the internal working of stars. "
The reaserch finding is published in the 'Astrophysical Journal Letters'.