出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We use the visually brightest A-type supergiant Deneb (A2 Ia) as benchmark for testing a spectroscopic
analysis technique developed for quantitative studies of BA-type supergiants. Our NLTE
spectrum synthesis technique allows us to derive stellar parameters and elemental abundances
with unprecedented accuracy. 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. 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.
The basic atmospheric parameters Teff = 8525±75K and logg = 1.10±0.05 dex (cgs) and
the distance imply the following fundamental parameters for Deneb: Mspec = 17±3M⊙,
L = 1.77±0.29 · 105L⊙ and R = 192±16 R⊙. The derived He and CNO abundances indicate
mixing with nuclear processed matter. The high N/C ratio of 4.64±1.39 and a N/O ratio of
0.88±0.07 (mass fractions) could in principle be explained by evolutionary models with initially
very rapid rotation. A mass of ∼22M⊙ is implied for the progenitor on the zero-age main sequence,
i.e. it was a late O-type star. Significant mass-loss has occurred, probably enhanced
by pronounced centrifugal forces. The observational constraints favour a scenario for the evolution
of Deneb where the effects of rotational mixing may be amplified by an interaction with a
magnetic field. Analogous analyses of such highly luminous BA-type supergiants will allow for
precision studies of different galaxies in the Local Group and beyond.
