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2021ApJ...912..157R - Astrophys. J., 912, 157-157 (2021/May-2)

Extreme r-process enhanced stars at high metallicity in Fornax.

REICHERT M., HANSEN C.J. and ARCONES A.

Abstract (from CDS):

We present and discuss three extremely r-process enhanced stars located in the massive dwarf spheroidal galaxy Fornax. These stars are very unique with an extreme Eu enrichment (1.25 <= [Eu/Fe]<=1.45) at high metallicities (-1.3 <= [Fe/H]<=-0.8). They have the largest Eu abundances ever observed in a dwarf galaxy opening new opportunities to further understand the origin of heavy elements formed by the r-process. We derive stellar abundances of Co, Zr, La, Ce, Pr, Nd, Er, and Lu using one-dimensional, local thermodynamic equilibrium codes and model atmospheres in conjunction with state-of-the art yield predictions. We derive Zr in the largest sample of stars (105) known to date in a dwarf galaxy. Accurate stellar abundances combined with a careful assessment of the yield predictions have revealed three metal-rich stars in Fornax showing a pure r-process pattern. We define a new class of stars, namely, Eu-stars, as r-II stars (i.e., [Eu/Fe] > 1) at high metallicities (i.e., [Fe/H] >= -1.5). The stellar abundance pattern contains Lu, observed for the first time in a dwarf galaxy, and reveals that a late burst of star formation has facilitated extreme r-process enhancement late in the galaxy's history (<4 Gyr ago). Due to the large uncertainties associated with the nuclear physics input in the yield predictions, we cannot yet determine the r-process site leading to the three Eu-stars in Fornax. Our results demonstrate that extremely r-rich stars are not only associated with ultra-faint low-mass dwarf galaxies, but can be born also in massive dwarf galaxies.

Abstract Copyright: © 2021. The American Astronomical Society. All rights reserved.

Journal keyword(s): Chemical abundances - R-process - Nucleosynthesis - Fornax dwarf spheroidal galaxy - Dwarf spheroidal galaxies - Chemically peculiar stars

Simbad objects: 116

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