A search for Mg-poor stars using LAMOST survey data

Abstract

Most Galactic metal-poor stars exhibit enhanced α-abundances (e.g. [Mg/Fe] ∼ +0.4) according to previous studies of stellar chemical compositions. However, a handful of metal-poor stars with large deficiencies in Mg (e.g. [Mg/Fe] ∼ −0.2) show severe departures from this α-enhancement trend. The sub-solar [Mg/Fe] ratios of these anomalous stars indicate that they possess different chemical enrichment histories than the majority of Galactic metal-poor stars. In previous work, we presented a method to select Mg-poor metal-poor stars from low-resolution SDSS spectra based on a spectral matching technique. In this paper, a similar method is applied to low-resolution (R ∼ 1800) LAMOST spectra. Stellar [Mg/Fe] abundances are determined by using stellar parameters delivered by the LAMOST Data Release 2 catalog. From a sample of ∼ 60 000 stars with atmospheric parameters in the range Teff = [5500, 6500] K and [Fe/H] = [−2.4, +0.5], we select 15 candidate Mg-poor metal-poor stars.