J-PLUS: Searching for very metal-poor star candidates using the SPEEM pipeline

¹ Observatório Nacional - MCTI (ON), Rua Gal. José Cristino 77, São Cristóvão, 20921-400, Rio de Janeiro, Brazil
e-mail: carlosgalarza@on.br
² NSF’s NOIRLab, 950 N. Cherry Ave., Tucson, AZ 85719, USA
³ Instituto de Astrofísica de Canarias, Vía Láctea, 38205 La Laguna, Tenerife, Spain
⁴ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
⁵ Department of Astronomy, Beijing Normal University, Beijing 100875, PR China
⁶ Centro de Estudios de Física del Cosmos de Aragón (CEFCA/CSIC), Plaza San Juan 1, 44001, Teruel, Spain
⁷ Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134, South Korea
⁸ Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁹ Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK
¹⁰ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, GR 15236 Penteli, Greece
¹¹ Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, R. do Matão 1226, 05508-090, São Paulo, Brazil
¹² Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
¹³ Department of Astronomy, University of Michigan, 930 Dennison Bldg., Ann Arbor, MI 48109-1090, USA
¹⁴ Eureka Scientific Inc., 2452 Delmer St. Suite 100, Oakland, CA 94602, USA
¹⁵ Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487, USA
¹⁶ Instituto de Astrofísica de Andalucía–CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁷ Universidad de Alicante, Carr. de San Vicente del Raspeig, s/n, 03690 San Vicente del Raspeig, Alicante, Spain
¹⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206, Tenerife, Spain

Received: 5 July 2021
Accepted: 23 September 2021

Abstract

Context. We explore the stellar content of the Javalambre Photometric Local Universe Survey (J-PLUS) Data Release 2 and show its potential for identifying low-metallicity stars using the Stellar Parameters Estimation based on Ensemble Methods (SPEEM) pipeline.

Aims. SPEEM is a tool used to provide determinations of atmospheric parameters for stars and separate stellar sources from quasars based on the unique J-PLUS photometric system. The adoption of adequate selection criteria allows for the identification of metal-poor star candidates that are suitable for spectroscopic follow-up investigations.

Methods. SPEEM consists of a series of machine-learning models that use a training sample observed by both J-PLUS and the SEGUE spectroscopic survey. The training sample has temperatures, T_eff, between 4800 K and 9000 K, values of log g between 1.0 and 4.5, as well as −3.1 < [Fe/H] < +0.5. The performance of the pipeline was tested with a sample of stars observed by the LAMOST survey within the same parameter range.

Results. The average differences between the parameters of a sample of stars observed with SEGUE and J-PLUS, obtained with the SEGUE Stellar Parameter Pipeline and SPEEM, respectively, are ΔT_eff ~ 41 K, Δlog g ~ 0.11 dex, and Δ[Fe/H] ~ 0.09 dex. We define a sample of 177 stars that have been identified as new candidates with [Fe/H] < −2.5, with 11 of them having 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.

Conclusions. Using SPEEM in combination with the J-PLUS filter system has demonstrated their potential in estimating the stellar atmospheric parameters (T_eff, 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.