Investigation of the helium enhancement in a super lithium-rich giant HD 77361

Abstract

In this work, the helium-enhancement (He-enhancement) in the lithium-rich (Li-rich) K-giant HD 77361 is investigated using the strengths of the MgH band and the Mg I lines. The detailed abundance analysis and also the synthesis of the MgH band and the Mg I lines has been carried out for HD 77361. One would expect, within uncertainities, same Mg abundance from both the MgH and Mg I lines. But, we found that Mg abundance derived from MgH lines is significantly less than the abundance from Mg I lines, and this difference cannot be reconciled by changing the stellar parameters within the uncertainties, implying He enhancement in star’s photosphere. The He enhancement in the atmospheres is estimated by using models of different He/H ratios so that both the lines, MgH as well as Mg I, return the same Mg abundance for the adopted model’s He/H ratio. We found He=H ¼ 0:4 0:1 as the value for HD 77361, the normal value of He=H ¼ 0:1. Knowing the amount of He-enhancement in the Li-rich giants is a strong clue for understanding the scenarios responsible for the Li and He enrichment. The analysis and results are discussed.