First r-process enhanced star confirmed as a member of the Galactic bulge

¹ Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden
e-mail: rebecca@astro.lu.se
² Department of Physics and Astronomy, ICLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547, USA
³ Université Côte-d’Azur, Observatoire de la Côte d'Azur, Laboratoire Lagrange, CNRS, Blvd de l’Observatoire, 06304 Nice, France
⁴ Materials Science and Applied Mathematics, Malmö University, 205 06 Malmö, Sweden
⁵ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 20 June 2022
Accepted: 10 October 2022

Abstract

Aims. Stars with strong enhancements of r-process elements are rare and tend to be metal-poor, generally with [Fe/H] < −2 dex, and located in the halo. In this work, we aim to investigate a candidate r-process enriched bulge star with a relatively high metallicity of [Fe/H] ~ − 0.65 dex and to compare it with a previously published r-rich candidate star in the bulge.

Methods. We reconsidered the abundance analysis of a high-resolution optical spectrum of the red-giant star 2MASS J18082459-2548444 and determined its europium (Eu) and molybdenum (Mo) abundance, using stellar parameters from five different previous studies. Applying 2MASS photometry, Gaia astrometry, and kinematics, we estimated the distance, orbits, and population membership of 2MASS J18082459-2548444 and a previously reported r-enriched star 2MASS J18174532-3353235.

Results. We find that 2MASS J18082459-2548444 is a relatively metal-rich, enriched r-process star that is enhanced in Eu and Mo, but not substantially enhanced in s-process elements. There is a high probability that it has a Galactic bulge membership, based on its distance and orbit. We find that both stars show r-process enhancement with elevated [Eu/Fe]-values, even though 2MASS J18174532-3353235 is 1 dex lower in metallicity. Additionally, we find that the plausible origins of 2MASS J18174532-3353235 to be either that of the halo or the thick disc.

Conclusions. We conclude that 2MASS J18082459-2548444 represents the first example of a confirmed r-process enhanced star confined to the inner bulge. We assume it is possibly a relic from a period of enrichment associated with the formation of the bar.