Galarza, Carlos Andrés, Daflon, Simone, Placco, Vinicius M., Allende-Prieto, Carlos, Fernandes, Marcelo Borges, Yuan, Haibo, López-Sanjuan, Carlos, Lee, Young Sun, Solano, Enrique, Jiménez-Esteban, F., Sobral, David, Candal, Alvaro Alvarez, Pereira, Claudio B., Akras, Stavros, Martín, Eduardo, Teja, Yolanda Jiménez, Cenarro, Javier, Cristóbal-Hornillos, David, Hernández-Monteagudo, Carlos, Marín-Franch, Antonio, Moles, Mariano, Varela, Jesús, Ramió, Héctor Vázquez, Alcaniz, Jailson, Dupke, Renato, Ederoclite, Alessandro, Sodré Jr., Laerte, and Angulo, Raul E.
We explore the stellar content of the Javalambre Photometric Local Universe Survey (J-PLUS) Data Release 2 and show its potential to identify low-metallicity stars using the Stellar Parameters Estimation based on Ensemble Methods (SPEEM) pipeline. SPEEM is a tool to provide determinations of atmospheric parameters for stars and separate stellar sources from quasars, using the unique J-PLUS photometric system. The adoption of adequate selection criteria allows the identification of metal-poor star candidates suitable for spectroscopic follow-up. SPEEM consists of a series of machine learning models which uses a training sample observed by both J-PLUS and the SEGUE spectroscopic survey. The training sample has temperatures Teff between 4\,800 K and 9\,000 K; $\log g$ between 1.0 and 4.5, and $-3.1<[Fe/H]<+0.5$. The performance of the pipeline has been tested with a sample of stars observed by the LAMOST survey within the same parameter range. The average differences between the parameters of a sample of stars observed with SEGUE and J-PLUS, which were obtained with the SEGUE Stellar Parameter Pipeline and SPEEM, respectively, are $\Delta Teff\sim 41$ K, $\Delta \log g\sim 0.11$ dex, and $\Delta [Fe/H]\sim 0.09$ dex. A sample of 177 stars have been identified as new candidates with $[Fe/H]<-2.5$ and 11 of them have been observed with the ISIS spectrograph at the William Herschel Telescope. The spectroscopic analysis confirms that $64\%$ of stars have $[Fe/H]<-2.5$, including one new star with $[Fe/H]<-3.0$. SPEEM in combination with the J-PLUS filter system has shown the potential to estimate the stellar atmospheric parameters (Teff, $\log g$, and [Fe/H]). The spectroscopic validation of the candidates shows that SPEEM yields a success rate of $64\%$ on the identification of very metal-poor star candidates with $[Fe/H]<-2.5$., Comment: Accepted for publication in the Astronomy & Astrophysics Journal