Testing Chemical Tagging with LAMOST: Intrinsic Abundance Dispersion of Subgiant Stars in the Galactic Disk

Abstract: The scatter in elemental abundances among stars of similar age and metallicity reflects chemical inhomogeneity in their birth environments, making abundance scatter a key observable for chemical-tagging studies of Galactic formation and evolution. Using a large sample of subgiant stars with precise ages and elemental abundances derived from LAMOST low-resolution spectra, we investigate the intrinsic chemical abundance scatter of the low-$α$ thin disk near the solar neighborhood ($7 < R < 10$ kpc). We model the abundance ratio [X/Fe], for each of the 19 elements of concern, as a function of age, [Fe/H], and [Mg/Fe], and deduce the intrinsic dispersions with a forward modelling technique. Our results confirm previous findings that the intrinsic scatters are small, typically $\lesssim0.05$~dex, for light elements (C, Al), $α$-elements (O, Mg, Si, Ca, Ti), and iron-peak elements (Mn, Ni). A dedicated analysis of M67 yields similarly small scatter values for these elements, implying limited discriminatory power from light-element abundances alone. In contrast, neutron-capture elements exhibit substantially larger scatters, typically $\gtrsim$0.1 dex, which are significantly larger than those of M67 member stars ($\sim$0.07~dex). In particular, our analysis suggests that the abundance variations of individual neutron-capture elements cannot be explained by a single tracer such as [Ba/Fe]. These findings clarify the utility of neutron-capture elements for chemical tagging and highlight the potential of low-resolution spectroscopy in such studies.