The R-Process Alliance: Discovery of a low-alpha, r-Process-Enhanced Metal-Poor Star in the Galactic Halo
astro-ph.SR
/ Authors
Charli M. Sakari, Ian U. Roederer, Vinicius M. Placco, Timothy C. Beers, Rana Ezzeddine, Anna Frebel, Terese Hansen, Christopher Sneden, John J. Cowan, George Wallerstein
and 17 more authors
Elizabeth M. Farrell, Kim A. Venn, Gal Matijevic, Rosemary F. G. Wyse, Joss Bland-Hawthorn, Cristina Chiappini, Kenneth C. Freeman, Brad K. Gibson, Eva K. Grebel, Amina Helmi, Georges Kordopatis, Andrea Kunder, Julio Navarro, Warren Reid, George Seabroke, Matthias Steinmetz, Fred Watson
/ Abstract
A new moderately r-process-enhanced metal-poor star, RAVE J093730.5-062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937-0626 is likely a horizontal branch star. At [Fe/H] = -1.86, J0937-0626 is found to have subsolar [X/Fe] ratios for nearly every light, alpha, and Fe-peak element. The low [alpha/Fe] ratios can be explained by an ~0.6 dex excess of Fe; J0937-0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H] = -2.5 suggests that J0937-0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937-0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937-0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937-0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.