Quantitative spectroscopy of Deneb

TL;DR

This study performs a detailed, high-precision spectroscopic analysis of the supergiant star Deneb, refining its fundamental parameters and chemical composition using advanced NLTE techniques and high-quality observational data.

Contribution

It introduces a sophisticated hybrid NLTE spectrum synthesis method applied to Deneb, achieving unprecedented accuracy in stellar parameter determination and resolving previous inconsistencies.

Findings

Accurate stellar parameters for Deneb established

Chemical abundances including CN-processed matter measured

Stellar wind properties derived from H_alpha line-profile fitting

Abstract

Quantitative spectroscopy of luminous BA-type supergiants offers a high potential for modern astrophysics. The degree to which we can rely on quantitative studies of this class of stars as a whole depends on the quality of the analyses for benchmark objects. We constrain the basic atmospheric parameters and fundamental stellar parameters as well as chemical abundances of the prototype A-type supergiant Deneb to unprecedented accuracy (Teff = 8525 +/- 75 K, log(g) = 1.10 +/- 0.05 dex, M_spec = 19 +/- 3 M_sun, L = 1.96 +/- 0.32 *10^5 L_sun, R = 203 +/- 17 R_sun, enrichment with CN-processed matter) by applying a sophisticated hybrid NLTE spectrum synthesis technique which has recently been developed and tested. The study is based on a high-resolution and high-S/N spectrum obtained with the Echelle spectrograph FOCES on the Calar Alto 2.2m telescope. Practically all inconsistencies reported in earlier studies are resolved. Multiple metal ionization equilibria and numerous hydrogen lines from the Balmer, Paschen, Brackett and Pfund series are brought into match simultaneously for the stellar parameter determination. Stellar wind properties are derived from H_alpha line-profile fitting using line-blanketed hydrodynamic non-LTE models. A self-consistent view of Deneb is thus obtained, allowing us to discuss its evolutionary state in detail by comparison with the most recent generation of evolution models for massive stars. (abridged)