The C I , Na I D , and H \alpha lines of the post-AGB binary HR 4049 have been studied .
Na I D variability results from a photospheric absorption component ( [ Na/H ] = -1.6 \pm 0.2 ) which follows the velocity of the primary and a stationary , non-photospheric component .
An emission component is attributed to the circumbinary disc , and an absorption component to mass-loss from the system with a velocity of 5.3 \pm 0.5 km s ^ { -1 } .

The H \alpha 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 km s ^ { -1 } .
The intensity variations are largely attributed to a differential amount of reddening towards the H \alpha emitting region and the stellar continuum .
The radial velocities suggest that the H \alpha emission moves in phase with the primary , but with a slightly lower velocity amplitude .
From this we infer that the H \alpha emission comes from outside the orbit of the primary , but still gravitational bound to the primary .
H \alpha also shows a weak emission feature at -21.3 \pm 3.5 km s ^ { -1 } , which originates from the circumbinary disc and a weak absorption feature at -7.5 \pm 1.6 km s ^ { -1 } due to absorption by the circumbinary disc .

We propose two competing models that could account for the observed velocity and intensity variations of the H \alpha 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 \alpha 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 \alpha emission of HR 4049 with those of early type T-Tauri stars ( e.g SU Aur ) .