Mining the GALAH Data. I. Study of Five Super Lithium-rich Metal-poor Giants

Abstract

The presence of a large amount of Li in giants is still a mystery. Most of the super Li-rich (SLR) giants reported in recent studies are in the solar metallicity regime. Here, we study the five metal-poor SLRs from the Galactic Archeology with HERMES Data Release 3, with their [Fe/H] ranging from −1.35 to −2.38 with lithium abundance of A (Li) ≥ 3.4 dex. The asteroseismic analysis reveals that none are on the red giant branch. The average period spacing (Δ P ) values indicate giants are in the core He-burning phase. All of them are low-mass giants ( M < 1.5 M _⊙ ). Their location in the Hertzsprung–Russell diagram suggests one of them is in the red clump (RC) phase, and interestingly, the other four are much brighter and coincide with the early asymptotic giant branch phase. The analysis of the abundance reveals that C, O, Na, Ba, and Eu are normal in giants of respective metallicities and evolutionary phases. Further, we did not find any strong evidence of the presence of dust in the form of infrared excess or binarity from the available radial velocity data. We discuss a few scenarios for the existence of SLRs at higher luminosity, including past merger events. Our findings will help in understanding the production and evolution of Li among giants, in particular, during the RC phase and the post-RC phase.

Keywords

• Chemically peculiar stars
• Giant stars
• Lithium stars