The R-Process Alliance: Hunting for gold in the near-UV spectrum of 2MASS J05383296–5904280^★

¹ Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
² Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
³ Joint Institute for Nuclear Astrophysics – Center for the Evolution of the Elements (JINA-CEE), USA
⁴ Department of Astronomy, University of Florida, Bryant Space Science Center, Gainesville, FL 32611, USA
⁵ Department of Physics and Astronomy, University of Notre Dame, Notre Dame, IN 46556, USA
⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
⁸ NSF NOIRLab, Tucson, AZ 85719, USA
⁹ Department of Physics and Astronomy, San Francisco State University, San Francisco, CA 94132, USA
¹⁰ Department of Astronomy & Astrophysics, University of Chicago, 5640 S Ellis Avenue, Chicago, IL 60637, USA
¹¹ Mitchell Institute for Fundamental Physics and Astronomy and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
¹² Department of Physics, Zarqa University, Zarqa 13110, Jordan
¹³ Jordanian Astronomical Virtual Observatory, Zarqa University, Zarqa 13110, Jordan
¹⁴ Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA

^★★ Corresponding author: thidemannhansen@gmail.com

Received: 13 February 2025
Accepted: 17 March 2025

Abstract

Context. Over the past few years, the R-Process Alliance (RPA) has successfully carried out a search for stars that are highly enhanced in elements produced via the rapid neutron-capture (r-) process. In particular, the RPA has identified a number of relatively bright, highly r-process-enhanced (r-II) stars, suitable for observations with the Hubble Space Telescope (HST), facilitating abundance derivation of elements such as gold (Au) and cadmium (Cd).

Aims. This paper presents the detailed abundances derived for the metal-poor ([Fe/H] = −2.55) highly r-process-enhanced ([Eu/Fe] = +1.29) r-II star 2MASS J05383296–5904280.

Methods. One-dimensional local thermodynamic equilibrium (LTE) elemental abundances were derived via equivalent width and spectral synthesis using high-resolution high signal-to-noise near-UV HST/STIS and optical Magellan/MIKE spectra.

Results. Abundances were determined for 43 elements, including 26 neutron-capture elements. In particular, abundances of the rarely studied elements Nb, Mo, Cd, Lu, Os, Pt, and Au are derived from the HST spectrum. These results, combined with RPA near-UV observations of two additional r-II stars, increase the number of Cd abundances derived for r-process-enriched stars from seven to ten and Au abundances from four to seven. A large star-to-star scatter is detected for both of these elements, highlighting the need for more detections enabling further investigations, specifically into possible non-LTE effects.