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

Abstract

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 ($\le$ 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.

10 pages, 7 figures, 1 table, accepted in Astrophysical Journal Letters

References in corpus (14)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• The LAMOST Stellar Parameter Pipeline at Peking University --- LSP3
• Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
• linemake: An Atomic and Molecular Line List Generator
• Discovery of ubiquitous lithium production in low-mass stars
• Most Lithium-rich Low-mass Evolved Stars Revealed as Red Clump stars by Asteroseismology and Spectroscopy
• Survey of Li-rich giants among Kepler and LAMOST fields: Determination of Li-rich giants Evolutionary Phase
• A helium-flash-induced mixing event can explain the lithium abundances of red clump stars
• Study of Lithium Rich Giants with the GALAH Spectroscopic Survey
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• The Lithium Abundances from the Large Sky Area Multi-object Fiber Spectroscopic Telescope Medium-resolution Survey. I. The Method
• Lithium in red giants: the roles of the He-core flash and the luminosity bump

Cited by in corpus (2)

• Chemical Compositions of Red Giant Stars in the Old Open Cluster NGC 7789
• Angular momentum and lithium transport from main sequence to sub-giant and red giant low-mass stars