Time-Dependent Spectral Feature Variations of the FS CMa Star HD 50138

HD 50138 (V743 Mon, MWC 158, or IRAS 06491-0654) is a B[e] star of the FS CMa type. It is supposed to be a post-main-sequence star, which is still not highly evolved. The presence of a gaseous and dusty envelope precludes direct observations of the central object, and the possible binarity and physical nature of HD 50138 remains unclear. We present a long-term spectroscopic monitoring of this object over the last 20 years (Jeřabkova et al. 2016). Based on the obtained data, we confirm a quasi-periodic behavior of the object's spectral variability with two newly found long periods manifested in the Halpha and forbidden [O I] lines. The rotating structures around the object are supported by the detection of moving humps in the Halpha profile. Our results are consistent with either mass transfer in a binary system or the presence of an outflowing disk. Since our data cannot confirm the presence of a binary companion, the origin of such systems remains an interesting problem for further investigation.