SPLUS J142445.34-254247.1: An R-Process Enhanced, Actinide-Boost, Extremely Metal-Poor star observed with GHOST

• DOI: 10.48550/arxiv.2310.17024
• Publication Date: 2023-01-01
• Authors: Placco, Vinicius M.; Almeida-Fernandes...; 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, Ma...; 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
• Keywords: Astrophysics - Solar and Stellar Astrophysics; 13. Climate action; Astrophysics of Galaxies (astro-ph.GA); FOS: Physical sciences; 7. Clean energy; Astrophysics - Astrophysics of Galaxies; Solar and Stellar Astrophysics (astro-ph.SR)

We report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process. This star was first selected as a metal-poor candidate from its narrow-band 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 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 logeps(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 was 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 Msun, and the heavy-element (Z>=38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66Msun and 1.27Msun) 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.<br/>26 pages, 11 figures, accepted for publication on ApJ<br/>