A Search for Strongly Mg-enhanced Stars from the Sloan Digital Sky Survey

Strongly Mg-enhanced stars with [Mg/Fe] $>$ 1.0 show peculiar abundance patterns and hence are of great interest for our understanding of stellar formation and chemical evolution of the Galaxy. A systematical search for strongly Mg-enhanced stars based on the low-resolution $(R\simeq2000)$ spectra of the Sloan Digital Sky Survey (SDSS) is carried out by finding the best matched synthetic spectrum to the observed one in the region of Mg I b lines around $\lambda$5170\AA$~$via a profile matching method. The advantage of our method is that fitting parameters are refined by reproducing the [Mg/Fe] ratios of 47 stars from very precise high-resolution spectroscopic (HRS) analysis by Nissen and Schuster (2010); and these parameters are crucial to the precision and validity of the derived Mg abundances. As a further check of our method, Mg abundances are estimated with our method for member stars in four Galactic globular clusters (M92, M13, M3, M71) which cover the same metallicity range as our sample, and the results are in good agreement with those of HRS analysis in the literature. The validation of our method is also proved by the agreement of [Mg/Fe] between our values and those of HRS analysis by Aoki et al.(2013). Finally, 33 candidates of strongly Mg-enhanced stars with [Mg/Fe]$>$1.0 are selected from 14850 F and G stars. Follow-up observations will be carried out on these candidates with high-resolution spectroscopy by large telescopes in the near future, so as to check our selection procedure and to perform a precise and detailed abundance analysis and to explore the origins of these stars.