Chemical homogeneity and sulfur deficiency in the early B-type stars of the λ Orionis group

Abstract

ABSTRACT We present a detailed abundance analysis of nine early B-type stars in the λ Orionis group. High- and medium-resolution spectra of the target stars were observed at the Ankara University Kreiken Observatory or acquired from the European Southern Observatory and Observatoire de Haute-Provence archives. The atmospheric parameters of each star were estimated from the hydrogen Balmer, ionized silicone, and helium lines. Non-LTE model atmosphere calculations determined the precise abundances of helium, carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron from the spectra of each target star. While the abundances of the light elements He, C, N, O, Ne, Si, and also Fe are close to solar, Mg, Al, and S are deficient, and Ar is overabundant compared to the Sun. The phosphorus absorption lines were only accessible on the optical spectra of HD 43112, HD 34989, 37 Ori, and HD 36895. The phosphorus mean abundance values of these four stars are underabundant compared to the Sun. Argon was only detected on the spectra of HD 43112 and HD 36262 and showed an overabundance of 0.33 dex. The sulfur element deficiency was detected in all stars except for 35 Orionis. Sulfur may be a good signature to distinguish the λ Orionis group members from the Orion star-forming complex. Overall, chemical homogeneity was detected in all B-type star members of the λ Orionis group. Furthermore, the mass and age of each member were calculated and plotted on the H–R diagram.