Untangling the Sources of Abundance Dispersion in Low-metallicity Stars II: Neutron Capture Elements

Abstract: We present the abundances of 23 elements, including 11 heavy elements (Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu) for up to 86 metal-poor (-2 < [Fe/H] < -1) subgiants. We use KORG, a state of the art spectral synthesis package, to derive 1D-LTE abundances from high-SNR and high-resolution spectra taken by the Large Binocular Telescope with the Potsdam Echelle Polarimetric and Spectroscopic Instrument. These precise spectra and abundance measurements minimize the impact of photon-noise (<0.06 dex), allowing us to robustly measure the intrinsic abundance scatter in [X/Fe]. After removing two stars with exceptional s-process enhancement, we find that the intrinsic scatter among the s- and r-process elements tends to be larger than for the lighter elements, with heavy element scatter ranging from 0.11 (Zn) to 0.27 (Eu) dex. Intrinsic abundance scatter could have multiple origins, including star-to-star variations in the ratios of nucleosynthetic sources as well as stochastic sampling of the progenitor supernovae properties, such as mass, rotation, and magnetic field strength. We explore the expected abundance scatter signature caused by stochastic sampling, finding that a fraction of both rapidly rotating CCSN and magnetorotationally driven SN are needed to reach the observed abundances and intrinsic scatter. This analysis is limited by the restrictive parameter spaces spanned by existing yield sets. A diverse, finely sampled grid of supernovae yields is needed to robustly model stochastic abundance scatter.