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The R-Process Alliance: A Very Metal-poor, Extremely r-process-enhanced Star with [Eu/Fe] = + 2.2, and the Class of r-III Stars
Name
Cain_2020_ApJ_898_40.pdf
Description
Published version
Size
944.76 KB
Format
Adobe PDF
Checksum (MD5)
fe0d3d31c57d7e7764327af614d5e7b6
Author(s)
Cain, M
Frebel, A
Ji, AP
Placco, VM
Ezzeddine, R
Roederer, IU
Hattori, K
Beers, TC
Meléndez, J
Hansen, TT
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Version
Final published version
Abstract
© 2020. The American Astronomical Society. All rights reserved. We report the discovery of J1521-3538, a bright (V = 12.2), very metal-poor ([Fe/H] = -2.8) strongly r-process-enhanced field horizontal branch star, based on a high-resolution, high signal-to-noise Magellan/MIKE spectrum. J1521-3538 shows the largest r-process element overabundance in any known r-process-enhanced star, with [Eu/Fe] = +2.2, and its chemical abundances of 22 neutron-capture elements closely match the scaled solar r-process pattern. J1521-3538 is also one of few known carbon-enhanced metal-poor stars with r-process enhancement (CEMP-r stars), as found after correcting the measured C abundance for the star's evolutionary status. We propose to extend the existing classification of moderately enhanced () r-I and strongly r-process enhanced () r-II stars to include an r-III class, for r-process stars such as J1521-3538, with [Eu/Fe] >+2.0 and [Ba/Eu] <-0.5, or ≪ 100 times the solar ratio of europium to iron. Using cosmochronometry, we estimate J1521-3538 to be 12.5±5 Gyr and 8.9±5 Gyr, using two different sets of initial production ratios. These ages are based on measurements of the Th line at 4019 Å and other r-process element abundances. This is broadly consistent with the old age of a low-mass, metal-poor field red horizontal branch star. J1521-3538 likely originated in a low-mass dwarf galaxy that was later accreted by the Milky Way, as evidenced by its highly eccentric orbit.
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DOI of Published Version
10.3847/1538-4357/ab97ba
