The R-Process Alliance: Analysis of limited-r stars^⋆

¹ Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: txylaki@lsw.uni-heidelberg.de
² Department of Astronomy, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden
³ Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA
⁴ JINA Center for the Evolution of the Elements, USA
⁵ Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32601, USA
⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101, USA
⁸ NSF’s NOIRLab, Tucson, AZ 85719, USA
⁹ Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
¹⁰ Department of Physics & Astronomy, San Francisco State University, San Francisco, CA 94132, USA
¹¹ Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712, USA

Received: 29 January 2024
Accepted: 20 March 2024

Abstract

Context. In recent years, the R-Process Alliance (RPA) has conducted a successful search for stars that are enhanced in elements produced by the rapid neutron-capture (r-)process. In particular, the RPA has uncovered a number of stars that are strongly enriched in light r-process elements, such as Sr, Y, and Zr. These so-called limited-r stars were investigated to explore the astrophysical production site(s) of these elements.

Aims. We investigate the possible formation sites for light neutron-capture elements by deriving detailed abundances for neutron-capture elements from high-resolution spectra with a high signal-to-noise ratio of three limited-r stars.

Methods. We conducted a kinematic analysis and a 1D local thermodynamic equilibrium spectroscopic abundance analysis of three stars. Furthermore, we calculated the lanthanide mass fraction (X_La) of our stars and of limited-r stars from the literature.

Results. We found that the abundance pattern of neutron-capture elements of limited-r stars behaves differently depending on their [Ba/Eu] ratios, and we suggest that this should be taken into account in future investigations of their abundances. Furthermore, we found that the X_La of limited-r stars is lower than that of the kilonova AT2017gfo. The latter seems to be in the transition zone between limited-rX_La and that of r-I and r-II stars. Finally, we found that unlike r-I and r-II stars, the current sample of limited-r stars is largely born in the Galaxy and is not accreted.