Abstract
Context. B[e] stars are anomalous objects around which extended circumstellar matter is present.
The observed properties of the central star are significantly affected by the surrounding material. Therefore, the use of standard synthetic spectra is disputable in this case and our capability to study these objects is limited.
One of the possibilities is to analyse variations of the spectral features. Long-term spectroscopic observations are required for this, but are not found in the literature.
For our study we choose the B[e] star HD 50138 of the FS CMa type because of the indication that this star is a post-main-sequence star, although still not highly evolved. Therefore, it can be a good object for testing evolutionary models.
Currently, HD 50138 is the most extensively observed FS CMa star which makes it an ideal object for modelling.Nacional San Pedro Martir (echelle, R similar to 18 000, 16 spectra, 2005-2013), and the 0.81 m telescope at Three College Observatory (echelle, R similar to 12 000, 26 spectra, 2013-2014). Methods.
We describe and analyse variations of the chosen lines. The measurements of the equivalent widths and radial velocities of the H alpha, H beta, and [O I] lambda lambda 6300, 6364 angstrom lines are presented.
The set of obtained spectra allows us to describe the changes on timescales from days to years.