A critical evaluation of the elemental abundances and evolutionary status of 15 Vul (HD 189849): the first identification of an evolved A_m star

Abstract

Understanding the evolution of metallic-line (${\rm A}_{\rm m}$) stars requires well-determined atmospheric parameters and abundance patterns of the selected candidates. In this study, we present a detailed abundance analysis of 15 Vul (HD 189849), identified as a marginal ${\rm A}_{\rm m}$ star, using a combination of equivalent width and spectrum synthesis techniques, under the local thermodynamic equilibrium assumption. We compare our findings with previous analyses of the star, providing critique on both their results and our own. Our results suggest that, although 15 Vul exhibits some underabundances of calcium and scandium, which are typically associated with ${\rm A}_{\rm m}$ stars, it might more accurately be identified as a normal A star in terms of its abundance pattern of all other elements and microturbulence velocity. The star's position on the Hertzsprung-Russell diagram, along with our findings, may indicate that it is potentially a classical ${\rm A}_{\rm m}$ star that has evolved into the subgiant phase as a 'quasi-normal' star. This may be the first identification of an evolved ${\rm A}_{\rm m}$ star.