Context. The lithium abundances in a few percent of giants exceed the value predicted by the standard stellar evolution models, and the mechanisms of Li enhancement are still under debate. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey has obtained over six million spectra in the past five years, and thus provides a great opportunity to search these rare objects and to more clearly understand the mechanisms of Li enhancement.
Aims: The aim of this work is to accurately measure the Li abundance and investigate the possible mechanisms of Li enrichment for a newly found super Li-rich giant, TYC 3251-581-1, located near the luminosity function bump with a low carbon isotopic ratio.
Methods: Based on the high-resolution spectrum we obtained the stellar parameters (Teff, logg, [Fe/H]), and determined the elemental abundances of Li, C, N, α, Fe-peak, r-process, s-process elements, and the projected rotational velocity. For a better understanding of the effect of mixing processes, we also derived the 12C to 13C ratio, and constrained the evolutionary status of TYC 3251-581-1 based on the BaSTI stellar isochrones.
Results: The super Li-rich giant TYC 3251-581-1 has A(Li) = 3.51, the average abundance of two lithium lines at λ = 6708 Å and 6104 Å based on the non-local thermodynamic equilibrium analysis. The atmospheric parameters show that our target locates on the luminosity function bump. The low carbon isotopic ratio (12C/13C = 9.0), a slow rotational velocity vsini = 2.2 km s-1, and no sign of IR excess suggest that additional mixing after first dredge up (FDU) should occur to bring internal synthesized Li to the surface. The low carbon ([C/Fe] -0.34) and enhanced nitrogen ([N/Fe] 0.33) are also consistent with the sign of mixing.
Conclusions: Given the evolutionary stage of TYC 3251-581-1 with the relatively low 12C/13C, the internal production which replenishes Li in the outer layer is the most likely origin of Li enhancement for this star.
Astronomy and Astrophysics
- Pub Date:
- July 2018
- stars: late-type;
- stars: individual: TYC 3251-581-1;
- stars: abundances;
- stars: chemically peculiar;
- Astrophysics - Solar and Stellar Astrophysics
- 7 pages, 6 figures, accepted for publication in A&