VELOCITY DISPERSIONS AND MEAN ABUNDANCES FOR ROMANS G5-K1 SPECTROSCOPIC GROUPS

Roman's four spectroscopic groups, weak CN, weak line, strong line, and 4150, are compared for kinematic characteristics with corresponding groups assigned by [Fe/H]. The mean orbital eccentricities and the U, V, and W velocity dispersions for the first three Roman groups correlate more strongly with mean metallicity than those of the corresponding [Fe/H] groups. The boundaries between the metallicity groups are only a few times greater than the mean errors of the metallicities themselves (approximately 0.1 dex), and the resulting spillover degrades the gradient significantly for the groups based on [Fe/H]. Thus, Roman's spectrographic groups more nearly define distinct kinematic properties than do the corresponding groups based only on metallicity. Her strong-line and weak-line groups are associated with the young thin disk and old thin disk, respectively, and her weak CN group is identified with the thick disk. Her 4150 group does not follow the pattern, but shows a sharp increase in [e], sigma(U), sigma(V), and sigma(W). The explanation might involve the birthplaces of these stars, which as a group have smaller Galactic orbits, with more rapid than average enrichment rates associated with velocity dispersions indicative of their formation ages. Quantitative methods should be developed to replicate (or even improve upon) her classification criteria, in order to increase the sample sizes for these Galactic components with reduced contamination from neighboring components.