Chemodynamical evidence of the HR 1614 moving group as a bar resonance

Abstract

Moving groups (MGs) are ensembles of disk stars that clump in velocity and action space. A multitude of explanations as to their origin has been attempted, from dissolved star clusters to resonances with the Galactic bar, or other non-axisymmetric perturbations. The object of this work, the old HR 1614 group, has in the past already been shown to not be a disrupted cluster in terms of its broad age and metallicity distribution. Thus its stars have more likely been trapped by the Milky Way bar at corotation. Here, we present a new study that aims to chemically and dynamically characterize this group in the context of such a resonance. To this end, we used MIKE/Magellan high-resolution, high signal-to-noise spectra of six member stars of the HR 1614 MG to determine the chemical abundance ratios for 24 elements, several for the first time in those stars. The Fe-abundances of our sample range from +0.13 to +0.38 dex and the majority of abundance ratios is fully in line with those of metal-rich Milky Way disk stars, with few exceptions. In particular, the group's eponym, HR 1614, is enhanced in essentially all abundances and coincides with the higher-[X/Fe] trends of the Milky Way's thick disk. All elements (but S and Ca) show significant intrinsic abundance scatter that argue against this MG having formed in a contained environment such as a dissolved cluster. Isochrone ages, tailored to the measured metallicities support earlier findings of a broad age mix in this group, ranging from 1 Gyr to as old as 8 Gyr. We performed an orbital frequency analysis in a Galactic potential that includes a rotating bar. Indeed, our sample stars fall onto thin resonances on corotation. Hence, our results support the idea that the HR 1614 MG is a resonantly perturbed disk feature, mustering a melange of stars from different parent populations in the inner Galaxy.