Lithium-Rich Stars in the LAMOST Survey

Abstract

Lithium is a key element for an observational study of stellar interiors. Its extreme fragility makes it a sensitive measure of the ages of young stars, and an excess abundance of lithium in a small fraction of evolved stars has driven significant research into their interior mixing processes and the potential for engulfment of giant planets.

The search for lithium in both of these young and evolved stars was undertaken by data mining the Large sky Area Multi-Object fibre Spectroscopic Telescope (LAMOST) survey. Utilising this survey of over 2 million F,G,K and M type stars, a spectral index at the lithium resonance line (670.8 nm) was measured for hundreds of thousands of potential candidates. Spectral line index is a measure of the magnitude difference between the flux of a feature of interest and the flux of the continuum and is commonly used in astronomy for various applications. This method was used effectively to identify lithium-rich candidates in spectra that had been continuum normalised, and were then matched with synthetic spectral templates to indicate the strength of the absorption. Limitations in spectral template fitting arise from molecular inclusions in the synthetic spectra for cooler stars and the precision of the LAMOST derived stellar parameters contribute to limitations in effectively selecting candidates and are discussed herein.

Based on visual selection of these candidates matched with synthetic spectral templates, 155 lithium-rich very low mass dwarf candidates and 1149 lithium-rich giants have been identified. The selection of lithium-rich giant candidates is unprecedented and if confirmed, could increase the known number of lithium-rich giants by an order of magnitude.