Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon III. HD 50138

TL;DR

This study analyzes twenty years of spectroscopic data of the B[e] star HD 50138, revealing variable spectral features, long-term periodicities, and evidence supporting a binary system with a complex, distorted circumstellar disc.

Contribution

It provides the first detailed long-term spectral variability analysis of HD 50138, proposing a binary system with a distorted disc as the most plausible model.

Findings

Identified two long periods of 3000 and 5000 days in spectral line variations.

Detected short-term periodicities of ~34 and ~50 days in radial velocity changes.

Supported the binary system hypothesis with a highly distorted disc structure.

Abstract

We analyse spectroscopic observations of the B[e] star HD 50138 (MWC 158, V743 Mon, or IRAS 06491-0654), a member of the FS CMa group, obtained over the last twenty years. Four different epochs are identified in the observational data, where the variability of the spectral features is substantially different. Additionally, two long periods of (3 000 +/- 500) and (5 000 +/- 1000) days are found in the variations of the equivalent widths of the H alpha and [OI] 6300 A lines and radial velocities of the H alpha line violet peak. Modest signatures of a regular period of ~34 days in the radial velocities of the H alpha red peak and H beta central depression are found in the season 2013/2014. The H alpha V/R changes indicate a periodicity of ~50 days. The correlations between individual spectral features significantly restricts the model of the object and suggest that it is most likely a binary system with a highly distorted disc with spiral arms around the primary component. At the same time, no obvious signs of the secondary component has been found in the object's spectrum.