  HD 50138 presents the B[e] phenomenon, but its nature is not clear yet. This
star is known to present spectral variations, which have been associated with
outbursts and shell phases. We analyze the line profile variability of HD 50138
and its possible origin, which provide possible hints to its evolutionary
stage, so far said to be close to the end of (or slightly beyond) the main
sequence. New high-resolution spectra of HD 50138 obtained with the HERMES
spectrograph over several nights (five of them consecutively) were analyzed,
allowing us to confirm short-term line profile variability. Our new data show
short-term variations in the photospheric lines. On the other hand, purely
circumstellar lines (such as [O I] lines) do not show such rapid variability.
The rotational velocity of HD 50138, V_rot = 90.3 +- 4.3 km/s, and the rotation
period, P = 3.64 +- 1.16 d, were derived from the He II 4026A photospheric
line. Based on the moment method, we confirm that the origin of this short-term
line profile variability is not stellar spots, and it may be caused by
pulsations. In addition, we show that macroturbulence may affect the profiles
of photospheric lines, as is seen for B supergiants. The location of HD 50138
at the end of (or slightly beyond) the main sequence, the newly detected
presence of line profile variability resembling pulsating stars, and
macroturbulence make this star a fascinating object.
