J-PLUS: Identification of low-metallicity stars with artificial neural networks using SPHINX

D. D. Whitten, V. M. Placco, T. C. Beers, A. L. Chies-Santos, C. Bonatto, J. Varela, D. Cristóbal-Hornillos, A. Ederoclite, T. Masseron, Y. S. Lee, S. Akras, M. Borges Fernandes, J. A. Caballero, A. J. Cenarro, P. Coelho, M. V. Costa-Duarte, S. Daflon, R. A. Dupke, R. Lopes de Oliveira, C. López-Sanjuan, A. Marín-Franch, C. Mendes de Oliveira, M. Moles, A. A. Orsi, S. Rossi, L. Sodré and H. Vázquez Ramió. 2019. J-PLUS: Identification of low-metallicity stars with artificial neural networks using SPHINX. Astronomy and Astrophysics 622, DOI: 10.1051/0004-6361/201833368

We present a new methodology for the estimation of stellar atmospheric parameters from narrow- and intermediate-band photometry of the Javalambre Photometric Local Universe Survey (J-PLUS), and propose a method for target pre-selection of low-metallicity stars for follow-up spectroscopic studies. Photometric metallicity estimates for stars in the globular cluster M15 are determined using this method.

Aims. By development of a neural-network-based photometry pipeline, we aim to produce estimates of effective temperature, T-eff, and metallicity, [Fe/H], for a large subset of stars in the J-PLUS footprint.

Methods. The Stellar Photometric Index Network Explorer, SPHINX, was developed to produce estimates of T-eff and [Fe/H], after training on a combination of J-PLUS photometric inputs and synthetic magnitudes computed for medium-resolution (R similar to 2000) spectra of the Sloan Digital Sky Survey. This methodology was applied to J-PLUS photometry of the globular cluster M15.

Results. Effective temperature estimates made with J-PLUS Early Data Release photometry exhibit low scatter, sigma(T-eff) = 91 K, over the temperature range 4500 < T-eff (K) < 8500. For stars from the J-PLUS First Data Release with 4500 < T-eff (K) < 6200, 85 +/- 3% of stars known to have [Fe/H] < -2.0 are recovered by SPHINX. A mean metallicity of [Fe/H] = 2.32 +/- 0.01, with a residual spread of 0.3 dex, is determined for M15 using J-PLUS photometry of 664 likely cluster members.

Conclusions. We confirm the performance of SPHINX within the ranges specified, and verify its utility as a stand-alone tool for photometric estimation of effective temperature and metallicity, and for pre-selection of metal-poor spectroscopic targets.

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