Spectral variability of the binary HR 4049

Abstract

The H$α$ profile varies with the orbital period. The two strong shell type emission peaks are identified as from one single broad emission feature with an absorption centered around -7.5~\kms. The intensity variations are largely attributed to a differential amount of reddening towards the H$α$ emitting region and the stellar continuum. The radial velocities suggest that the H$α$ emission moves in phase with the primary, but with a slightly lower velocity amplitude. We propose two competing models that could account for the observed velocity and intensity variations of the H$α$ profile. Model I: light from the primary reflects on a localized spot near the inner radius of the circumbinary disc which is closest to the primary. Model II: H$α$ emission originates in the outer layers of the extended atmosphere of the primary due to activity. These activities are locked to the position of the primary in its orbit. We discuss the similarities of variability and shape of the H$α$ emission of HR~4049 with those of early type T-Tauri stars (e.g SU~Aur).