A statistical method for the identification of stars enriched in neutron-capture elements from medium-resolution spectra

¹ Departament de Física Quàntica i Astrofísica, Universitat de Barcelona, C. Martí i Franquès, 1, 08028 Barcelona, Spain
e-mail: gerrinp@gmail.com
² Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona, C. Martí i Franquès, 1, 08028 Barcelona, Spain

Received: 16 July 2019
Accepted: 24 September 2019

Abstract

We present an automated statistical method that uses medium-resolution spectroscopic observations of a set of stars to select those that show evidence of possessing significant amounts of neutron-capture elements. Our tool was tested against a sample of ∼70 000 F- and G-type stars distributed among 215 plates from the Galactic Understanding and Exploration (SEGUE) survey, including 13 that were directed at stellar Galaxy clusters. Focusing on five spectral lines of europium in the visible window, our procedure ranked the stars by their likelihood of having enhanced content of this atomic species and identifies the objects that exhibit signs of being rich in neutron-capture elements as those scoring in the upper 2.5%. We find that several of the cluster plates contain relatively large numbers of stars with significant absorption around at least three of the five selected lines. The most prominent is the globular cluster M 3, where we measured a fraction of stars that are potentially rich in heavy nuclides, representing at least 15%.