Mining S-PLUS for Metal-poor Stars in the Milky Way

Abstract

This work presents the medium-resolution ( R ∼ 1500) spectroscopic follow-up of 522 low-metallicity star candidates from the Southern Photometric Local Universe Survey (S-PLUS). The objects were selected from narrowband photometry, taking advantage of the metallicity-sensitive S-PLUS colors. The follow-up observations were conducted with the Blanco and Gemini South telescopes, using the COSMOS and GMOS spectrographs, respectively. The stellar atmospheric parameters ( T eff , log g , and [Fe/H]), as well as carbon and α -element abundances, were calculated for the program stars in order to assess the efficacy of the color selection. Results show that 92 − 3 + 2 % of the observed stars have [Fe/H] ≤ −1.0, 83 − 3 + 3 % have [Fe/H] ≤ −2.0, and 15 − 3 + 3 % have [Fe/H] ≤ −3.0, including two ultra metal-poor stars ([Fe/H] ≤ −4.0). The 80th percentile for the metallicity cumulative distribution function of the observed sample is [Fe/H] = −2.04. The sample also includes 68 carbon-enhanced metal-poor stars. Based on the calculated metallicities, further S-PLUS color cuts are proposed, which can increase the fractions of stars with [Fe/H] ≤ −1.0 and ≤ −2.0 to 98% and 88%, respectively. Such high success rates enable targeted high-resolution spectroscopic follow-up efforts, as well as provide selection criteria for fiber-fed multiplex spectroscopic surveys.