Lithium abundances in giants as a function of stellar mass: An evidence for He-flash as the source of Li enhancement in low mass giants

• Published in: arXiv.org 2023-01
• Main Authors: Mallick, Anohita, Singh, Raghubar, Reddy, Bacham E
• Format: Article
• Language: English
• Subjects: Abundance; Lithium; Red giant stars; Stellar mass; Stellar seismology
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2301.10436

In this work, we studied the distribution of lithium abundances in giants as a function of stellar mass. We used a sample of 1240 giants common among Kepler photometric and LAMOST medium resolution (R \(\approx\) 7500) spectroscopic survey fields. The asteroseismic \(\Delta\)P - \(\Delta \nu\) diagram is used to define core He-burning red clump giants and red giant branch stars with inert He-core. Li abundances have been derived using spectral synthesis for the entire sample stars. Directly measured values of asteroseismic parameters \(\Delta\)P(or \(\Delta \Pi_1\)) and \(\Delta \nu\) are either taken from the literature or measured in this study. Of the 777 identified red clump giants, we found 668 low mass (\(\leq\) 2~M\(_{\odot}\)) primary red clump giants and 109 high mass (\(>\) 2~M\(_{\odot}\)) secondary red clump giants. Observed Li abundances in secondary red clump giants agree with the theoretical model predictions. The lack of Li-rich giants among secondary red clump giants and the presence of Li-rich, including super Li-rich giants, among primary red clump stars reinforces the idea that Helium-flash holds the key for Li enrichment among low-mass giants. The results will further constrain theoretical models searching for a physical mechanism for Li enhancement among low-mass red clump giants. Results also serve as observational evidence that only giants with mass less than \(\approx\) 2~M\(_{\odot}\) develop degenerate He-core and undergo He-flash.