SPLUS J142445.34–254247.1: An r-process–enhanced, Actinide-boost, Extremely Metal-poor Star Observed with GHOST

• Published in: The Astrophysical journal 2023-12, Vol.959 (1), p.60
• Main Authors: Placco, Vinicius M., Almeida-Fernandes, Felipe, Holmbeck, Erika M., Roederer, Ian U., Mardini, Mohammad K., Hayes, Christian R., Venn, Kim, Chiboucas, Kristin, Deibert, Emily, Gamen, Roberto, Heo, Jeong-Eun, Jeong, Miji, Kalari, Venu, Martioli, Eder, Xu, Siyi, Diaz, Ruben, Gomez-Jimenez, Manuel, Henderson, David, Prado, Pablo, Quiroz, Carlos, Ruiz-Carmona, Roque, Simpson, Chris, Urrutia, Cristian, McConnachie, Alan W., Pazder, John, Burley, Gregory, Ireland, Michael, Waller, Fletcher, Berg, Trystyn A. M., Robertson, J. Gordon, Hartman, Zachary, Jones, David O., Labrie, Kathleen, Perez, Gabriel, Ridgway, Susan, Thomas-Osip, Joanna
• Format: Article
• Language: English
• Subjects: Abundance; Astrophysics; Chemical abundances; High resolution spectroscopy; Metallicity; Metals; Milky Way; Narrow band photometry; Narrowband; Neutron stars; Neutrons; Nuclear capture; Spectroscopy; Star mergers; Stars; Stars & galaxies; Stellar atmospheres; Supernova; Thorium
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad077e

We report on a chemo-dynamical analysis of SPLUS J142445.34−254247.1 (SPLUS J1424−2542), an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process ( r -process). This star was first selected as a metal-poor candidate from its narrowband S-PLUS photometry and followed up spectroscopically in medium resolution with Gemini-South/GMOS, which confirmed its low-metallicity status. High-resolution spectroscopy was gathered with GHOST at Gemini-South, allowing for the determination of the chemical abundances for 36 elements, from carbon to thorium. At [Fe/H] = −3.39, SPLUS J1424−2542 is one of the lowest-metallicity stars with measured Th and has the highest log ϵ ( Th / Eu ) observed to date, making it part of the “actinide-boost” category of r -process–enhanced stars. The analysis presented here suggests that the gas cloud from which SPLUS J1424−2542 formed must have been enriched by at least two progenitor populations. The light-element ( Z ≤ 30) abundance pattern is consistent with the yields from a supernova explosion of metal-free stars with 11.3–13.4 M ⊙ , and the heavy-element ( Z ≥ 38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66 M ⊙ and 1.27 M ⊙ ) event. A kinematical analysis also reveals that SPLUS J1424−2542 is a low-mass, old halo star with a likely in situ origin, not associated with any known early merger events in the Milky Way.