The Cool Giant HD 77361 - A Super Li-Rich Star

TL;DR

This study confirms that the K giant HD 77361 is a super Li-rich star, using independent photometric and spectroscopic methods to accurately determine its stellar parameters and lithium abundance.

Contribution

The paper provides a detailed independent verification of the super Li-rich nature of HD 77361 through precise measurements and analysis, supporting the existence of this rare stellar group.

Findings

HD 77361 has a lithium abundance of log e(Li) = 3.75, exceeding initial levels.

The star's effective temperature is 4370 K and surface gravity is log g = 2.30.

The study confirms the existence of super Li-rich giants beyond previous uncertainties.

Abstract

Super Li-rich stars form a very small and enigmatic group whose existence cannot be explained in terms of the standard stellar evolution theory. The goal of our study is to check the reality of this group of cool giants based on an independent technique. We have carried out such a check using the K giant HD 77361 (HR 3597), which has previously been assigned to this rare type, as an example. We have redetermined the effective temperature Teff and surface gravity log g for this star. We have applied two different methods, photometric and spectroscopic, to estimate Teff (the accuracy of the Li-abundance determination depends significantly on this parameter). The value of log g has been found from the highly accurate parallax of this nearby star. To apply the photometric method of determining Teff, we have performed UBV observations of the star, which yielded V = 6.18 +/- 0.03, B - V = 1.13 +/- 0.01, and U - B = 1.18+/-0.05. The following parameters of the star have been found: effective temperature Teff = 4370+/- 100 K, surface gravity log g = 2.30 +/- 0.10, iron abundance log e(Fe) = 7.49 +/- 0.14, microturbulence Vt = 1.1 +/- 0.2 km/s, rotational velocity V sin i = 4.5 km/s, and mass M = 1.3 +/- 0.2 Msun. The lithium abundance has been determined from a non-LTE analysis of three Li I lines: the resonance line at 6707.8 ?A and the subordinate lines at 6103.6 and 8126.4 ?A (the latter in a blend with a CN molecular line). We have found a high lithium abundance, log e(Li) = 3.75 +/- 0.11, which exceeds considerably the initial abundance log e(Li) = 3.2 +/- 0.1 for young stars in the solar neighborhood. Thus, we have confirmed that the K giant HD 77361 actually belongs to the type of super Li-rich stars.