The Galactic unclassified B[e] star HD 50138

III. The short-term line profile variability of its photospheric lines^{⋆,⋆⋆,⋆⋆⋆}

¹ Observatório Nacional, Rua General José Cristino 77, 20921-400, São Cristovão Rio de Janeiro, Brazil
e-mail: borges@on.br; claudio@on.br
² Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
e-mail: kraus@sunstel.asu.cas.cz; oksala@sunstel.asu.cas.cz, nickeler@asu.cas.cz
³ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
e-mail: Peter.DeCat@oma.be; patricia.lampens@oma.be

Received: 3 August 2012
Accepted: 23 September 2012

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. 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, ν_rot = 90.3  ±  4.3 km s^-1, and the rotation period, P = 3.64  ±  1.16 d, were derived from the He i λ4026 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.

Conclusions. 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.