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1. The R-process Alliance: A Nearly Complete R-process Abundance Template Derived from Ultraviolet Spectroscopy of the R-process-enhanced Metal-poor Star HD 222925*

   https://doi.org/10.3847/1538-4365/ac5cbc  

   Roederer, Ian U. ; Lawler, James E. ; Den Hartog, Elizabeth A. ; Placco, Vinicius M. ; Surman, Rebecca ; Beers, Timothy C. ; Ezzeddine, Rana ; Frebel, Anna ; Hansen, Terese T. ; Hattori, Kohei ; et al ( June 2022 , The Astrophysical Journal Supplement Series)

   Abstract We present a nearly complete rapid neutron-capture process ( r -process) chemical inventory of the metal-poor ([Fe/H] = −1.46 ± 0.10) r -process-enhanced ([Eu/Fe] = +1.32 ± 0.08) halo star HD 222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 ≤ Z ≤ 90, including elements rarely detected in r -process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The r -process elements from Ba to Pb, including all elements at the third r -process peak, exhibit remarkable agreement with the solar r -process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends frommore »Ga to Se, Nb through Cd, and In through Te. The r -process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the r -process. The lanthanide fraction, log X La = −1.39 ± 0.09, is typical for r -process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar r -process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations.« less
2. The R -process Alliance: First Release from the Southern Search for R -process-enhanced Stars in the Galactic Halo

   https://doi.org/10.3847/1538-4357/aabacc  

   Hansen, Terese T. ; Holmbeck, Erika M. ; Beers, Timothy C. ; Placco, Vinicius M. ; Roederer, Ian U. ; Frebel, Anna ; Sakari, Charli M. ; Simon, Joshua D. ; Thompson, Ian B. ( May 2018 , The Astrophysical Journal)
3. The R -Process Alliance: Fourth Data Release from the Search for R -process-enhanced Stars in the Galactic Halo

   https://doi.org/10.3847/1538-4365/ab9c19  

   Holmbeck, Erika M. ; Hansen, Terese T. ; Beers, Timothy C. ; Placco, Vinicius M. ; Whitten, Devin D. ; Rasmussen, Kaitlin C. ; Roederer, Ian U. ; Ezzeddine, Rana ; Sakari, Charli M. ; Frebel, Anna ; et al ( August 2020 , The Astrophysical Journal Supplement Series)
4. The R -Process Alliance: Discovery of a Low- α , r -process-enhanced Metal-poor Star in the Galactic Halo

   https://doi.org/10.3847/1538-4357/ab0c02  

   Sakari, Charli M. ; Roederer, Ian U. ; Placco, Vinicius M. ; Beers, Timothy C. ; Ezzeddine, Rana ; Frebel, Anna ; Hansen, Terese ; Sneden, Christopher ; Cowan, John J. ; Wallerstein, George ; et al ( April 2019 , The Astrophysical Journal)
5. The R -Process Alliance: Chemical Abundances for a Trio of r -process-enhanced Stars—One Strong, One Moderate, and One Mild

   https://doi.org/10.3847/1538-4357/aad37d  

   Cain, Madelyn ; Frebel, Anna ; Gull, Maude ; Ji, Alexander P. ; Placco, Vinicius M. ; Beers, Timothy C. ; Meléndez, Jorge ; Ezzeddine, Rana ; Casey, Andrew R. ; Hansen, Terese T. ; et al ( September 2018 , The Astrophysical Journal)