First stars XVI. STIS/HST abundances of heavy-elements in the uranium-rich star CS 31082-001

TL;DR

This study provides a comprehensive analysis of heavy-element abundances in the uranium-rich star CS 31082-001, using UV and optical spectroscopy to enhance understanding of r-process nucleosynthesis.

Contribution

It offers the most complete set of r-process element abundances for CS 31082-001, including six elements not previously measured, and introduces the first NLTE+3D lead abundance in this star.

Findings

Derived 23 new neutron-capture element abundances.

Identified six elements (Ge, Mo, Lu, Ta, W, Re) not previously measured in this star.

Provided improved constraints on the r-process nucleosynthesis.

Abstract

Detailed abundances of the elements produced by r-process nucleosynthesis in various circumstances are our best observational clues to their origin, since the site(s) of r-element production is(are) still not known with certainty. A small fraction of extremely metal-poor (EMP) stars exhibit excesses of heavy neutron-capture elements produced in the r-process, and CS 31082-001 is among the 4 well-known r-process-enhanced EMP stars. Observations with HST/STIS provide abundances for elements observable only from the UV region. Here we aim to supplement the optical data with abundances from near-UV spectroscopy of the first and second peak of the r-elements, which are crucial to giving insight into the nucleosynthesis of the elements beyond iron. The UVES spectrum provided additional measurements, thereby improving the previous results. The spectra were analyzed with the OSMARCS LTE model atmosphere and with a consistent approach based on the spectrum synthesis code Turbospectrum to derive abundances of heavy elements in CS 31082-001, using updated oscillator strengths from the recent literature. We computed synthetic spectra for all lines of the elements of interest, checking for proper intensities and possible blends. We combined the abundances of heavy elements derived in previous works with the derivation of abundances from all reliable new list of lines, for the first and second peaks of r-elements. We were able to derive new abundances for 23 n-elements, 6 of them - Ge, Mo, Lu, Ta, W, and Re - were not available in previous works, making this star the most complete r-II object studied, with a total of 37 detections of n-capture elements. We also present the first NLTE+3D lead abundance in this star. The results provide improved constraints on the nature of the r-process.