The Herbig B0e star HD 53367: Circumstellar activity and evidence of binarity

Abstract

Aims. We investigate the spectroscopic behaviour of the young B0e star HD 53367 within a cooperative observing programme conducted from 1994 to 2005. Methods. The data include more than 100 high-resolution spectra collected at the Crimean Astronomical Observatory (CrAO) near Hα, Hβ, He I λ 5876, 6678 Å, DNa I, and O II λ6641 Å lines. Two spectra obtained at the Observatório do Pico dos Dias (LNA), in the spectral bands λλ 4575-4725 Å and λλ 5625-5775 Å, were used for spectral classification of HD 53367. The temporal behaviour of the circumstellar lines Hα and Hβ as well as the photospheric lines O II λ 6641A° and He I λ 6678 A° were investigated during different stages of the photometric activity of this object. Results. We confirm that the long-term photometric variability of HD 53367 is related to the alternation of two states of this object when the gaseous circumstellar envelope disappears and rises again. Both these processes start near the star and spread to the outlying parts of the envelope. We find that the radial velocities of He I and OII photospheric lines demonstrate a cyclic variability with a period of P = 183.7 days and semi-amplitude K = 19 km s-1. The radial velocity change is interpreted in the framework of a model in which the star is a component of an eccentric binary system. An orbital solution is derived and the system's parameters estimated. We find that the orbital eccentricity is e = 0.28, and the mean companion separation is 1.7 AU. Conclusions. Based on the estimated parameters, we conclude that the system consists of a massive (∼20 M⊙) main sequence primary BOe star, and a secondary which is most likely a 5 solar mass pre-main sequence object. We found evidence that the main part of the circumstellar gas in this system is concentrated near the secondary companion. Although the young age of HD 53367, its evolved primary BOe star seems to have already became a classical Be star exhibiting a specific alternation of the B-Be stages. © ESO 2006.