New Nitrogen and Carbon in AF-supergiants

TL;DR

This study recalculates nitrogen abundances in AF-supergiants using improved models, revealing significant mixing with CN-cycled gas and suggesting a link between metallicity and nitrogen enrichment, with implications for stellar evolution.

Contribution

It provides updated NLTE nitrogen abundances in AF-supergiants, highlighting the role of rotational mixing and metallicity effects in stellar evolution models.

Findings

Higher nitrogen abundances than previous estimates.

SMC stars show larger nitrogen enrichment, indicating metallicity dependence.

Evidence of past dredge-up events in SMC and possibly Galactic AF-supergiants.

Abstract

The AF-supergiants in the Galaxy and the SMC allow us to examine predictions from evolution models through their CNO abundances. In these proceedings, we recalculate the NLTE nitrogen abundances in 22 Galactic and 9 SMC A-supergiants using improved atomic data and model atmospheres to compare with new evolution models. The new abundances are higher than previously published values, and suggest that most of these stars have undergone substantial mixing with CN-cycled gas. While there is no clear relationship with mass, there is an apparent relation with metallicity since the SMC stars (including B-stars) have larger nitrogen enrichments. We suggest that rotational mixing is indicated from the main-sequence throughout the supergiant range, with more substantial rotational mixing in the SMC stars. In addition, the SMC AF-supergiants appear to have undergone the first dredge-up during a previous red giant phase, and possibly the Galactic AF-supergiants have as well. All abundances are compared to the new solar abundances from M. Asplund (this conference).