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 (Teff, logg, and [Fe/H]), as well as carbon and {alpha}-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.

Cone search capability for table J/ApJS/262/8/targets (Observing details (Table 1), Southern Photometric Local Universe Survey (S-PLUS) photometry (Table 2) and stellar parameters and abundances from the n-SSPP (Table 3))