Spectroscopic study of two O-type supergiants, Alpha Camelopardalis and 19 Cephei: model-atmosphere analysis.

We analyzed high dispersion spectra of a Cam and 19 Cep by using standard model-atmosphere techniques in the LTE approximation, to obtain the atmospheric parameters and element abundances, and to study how well the planar LTE models can interpret the observed spectra. Comparisons of the observations with the calculations were also made for the planar NLTE models. The main conclusions are as follows: (1) The final planar LTE models (Teff=29000K, logg=3.05, n(He)/n(H)--0.16, =20kms-1, and V sin j=120 km 1 for a Cam; Tef =30000 K, log g--3.30, n(He)/n(H)-- 0.12, --22.5 km 1, and V sin j--95 km 1 for 19 Cep) can predict satisfactorily the observations of the Paschen continuum, the Balmer jump, and the Balmer lines except for Ha ane H . (2) These observed quantities can be also satisfactorily predicted by the corresponding NLTE models in which n(He)/n(H)--0.10 and --0 km s ' are assumed (Teff=32500 K and log g--3.15 for a Cam; Teff=35000 K and log g--3.3 for 19 Cep). (3) a Cam and 19 Cep show no difference between their element abundances, and have the same element abundances as those of normal OB stars of Population I. However, neon is overabundant by a factor of 5 compared with the Sun. (4) Both the planar LTE and NLTE models cannot predict Ha and H , and fail to explain neutral and ionized helium lines in a consistent way. The planar LTE models fail to realize the ionization equilibria for high ionization stages of light elements (C iii/C iv and, to a less extent, 011/0111). (5) a Cam and 19 Cep show the characteristics similar to 0(f) and Oe stars, respectively. A dynamical atmospheric model consisting of a core and a halo might be required for late 0-type supergiants. Key words: Fine analysis; 0-type supergiants; Stellar atmospheres.