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Context. Over the past few years, theR-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, highlyr-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) highlyr-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 additionalr-II stars, increase the number of Cd abundances derived forr-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.
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The R -Process Alliance: detailed chemical composition of an r -process enhanced star with UV and optical spectroscopy
ABSTRACT We present a detailed chemical-abundance analysis of a highly r-process-enhanced (RPE) star, 2MASS J00512646-1053170, using high-resolution spectroscopic observations with Hubble Space Telescope/STIS in the UV and Magellan/MIKE in the optical. We determined abundances for 41 elements in total, including 23 r-process elements and rarely probed species such as Al ii, Ge i, Mo ii, Cd i, Os ii, Pt i, and Au i. We find that [Ge/Fe] = +0.10, which is an unusually high Ge enhancement for such a metal-poor star and indicates contribution from a production mechanism decoupled from that of Fe. We also find that this star has the highest Cd abundance observed for a metal-poor star to date. We find that the dispersion in the Cd abundances of metal-poor stars can be explained by the correlation of Cd i abundances with the stellar parameters of the stars, indicating the presence of NLTE effects. We also report that this star is now only the sixth star with Au abundance determined. This result, along with abundances of Pt and Os, uphold the case for the extension of the universal r-process pattern to the third r-process peak and to Au. This study adds to the sparse but growing number of RPE stars with extensive chemical-abundance inventories and highlights the need for not only more abundance determinations of these rarely probed species, but also advances in theoretical NLTE and astrophysical studies to reliably understand the origin of r-process elements.
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- PAR ID:
- 10495820
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 529
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 1917-1940
- Size(s):
- p. 1917-1940
- Sponsoring Org:
- National Science Foundation
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