Received 9 December 1999 / Accepted 25 May 2000
This study presents a detailed model atmosphere abundance analysis of Deneb which was performed using Kurucz LTE ATLAS9 model atmospheres. The atmospheric parameters were determined from Mg I/II and Fe I/II equilibrium, and by fitting the profile and optical region spectrophotometry. The compromise values which best satisfy these criteria are = 9000 K and log = 1.45. The Mg I, Mg II, Si II, Ti II, Cr II, Fe I, and Fe II lines yield microturbulences of 3.60, 6.50, 8.50, 8.00, 11.90, 3.60, and 10.40 km , respectively. An average microturbulence of 7 km was used for the other atomic species.
From a comparision of the synthetic spectrum with the observations, the best value for the rotational velocity is v sin i = 25 km , and for the macroturbulent velocity is = 14 km , which are similar to those of some earlier derived values. Also, the individual spectrograms have a range of radial velocity variation of 15 km which is approximately equal to macroturbulent velocity. These values of the macroturbulence and the range of radial velocity variation are close to the sum of the amplitudes (10.44 km ) of all the pulsation periods found by Lucy (1976), who also suggested that the surface motions of the atmosphere of Deneb can be identified with macroturbulence.
Deneb showed a definite helium underabundance with a well determined He/H value = 0.071. The CNO values (C being mildly deficient, N being in moderate excess, and an O being slightly deficient) are consistent with the mixing of the CNO-cycled products into the surface layers from the processed materials presumably dredged-up from the interior. Aluminium is mildly deficient by 0.24 dex with respect to solar value, while sulfur is moderately underabundant by 0.43 dex in Deneb. Mg and Si have the solar abundances. The metal abundances (Ca to Ni) tend to be greater than solar except for Sc which is slightly deficient. The heavy elements abundances (Sr, Y, and Zr) are all greater than solar. These abundance patterns conform to the common tendency seen with other normal Population I A supergiants found by Venn (1995a). The rare-earth elements (Ba, La, and Eu) which have been unexplored in other Galactic early A-type supergiants are significantly overabundant relative the Sun.
Key words: stars: individual: Deneb stars: fundamental parameters stars: abundances stars: evolution stars: supergiants
* Based on data obtained at the Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.
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© European Southern Observatory (ESO) 2000
Online publication: December 15, 2000