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

TL;DR

This study provides a detailed abundance analysis of 15 Vul, suggesting it may be an evolved Am star transitioning into a subgiant phase, marking the first such identification.

Contribution

It offers the first detailed abundance analysis indicating 15 Vul as a potentially evolved Am star, challenging previous classifications.

Findings

15 Vul shows underabundances of calcium and scandium.

The star's abundance pattern resembles a normal A star.

It may be an evolved Am star in the subgiant phase.

Abstract

Understanding the evolution of metallic-line (Am) stars requires well determined atmospheric parameters and abundance patterns of the selected candidates. In this study, we presented a detailed abundance analysis of 15 Vul (HD 189849), identified as a marginal Am star, using a combination of equivalent width and spectrum synthesis techniques, under the LTE assumption. We compared our findings to 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 Am stars, it might be more accurately 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 HR diagram, along with our findings, may indicate that it is potentially a classical Am star that has evolved into the subgiant phase as a "quasi-normal" star. This may be the first identification of an evolved Am star.