- for example Miroshnichenko et al. (2009)
- narrow
- stable; they show changes on the scale of months
- sometimes double-peaked
- [O I] λ λ 6 300, 6 364 Å is always present
- [S II] λ λ 6 716, 6 731 Å is usually present
- [N II] λ λ 6 548, 6 583 Å is usually present
- Forbidden emission lines allow the usage of the nebular diagnostic.
- Hα may be hundred times more intensive than the continuum
- large number of the Balmer lines ⇒ low density and stable medim (low turbulent velocity or rotation velocity)
- Hα is variable on the time-scale of days and weeks
- moving bumps across the line-profile were detected
- Resonance lines are almost always observed in the emission.
- Discrete absorption components of the resonance lines were detected in MWC 342, AS 225, AS 174, HD 328990, HD 50138. They are usually blue-shiftet, however the red-shift was also observed.
- The strong absorption of the iron group elements is observed under high inclination angles. The UV radiation is suppressed about an order of magnitude compare to the classical Be stars. (found by Steven N. Shore)
- Expanding layers that may even decelerate were detected Kučerová et al. (2013).
- Regular period of the radial velocities was found, e.g., in AS 386 (Khokhlov et al., 2018) and MWC 728 (Miroshnichenko et al., 2015).
- Most FS CMa stars show irregular variability. The period of individual cycles may grown up, e.g., in MWC 342 Kučerová et al. (2013) or HD 50138 Jeřábková et al. (2016) .
- Kluska et al. (2016) analysed VLTI/PIONIER data of HD 50138. They found a disk with a spot around the star. The disk shape changed in two years.
-
The photometry shows multiperiodic behaviour with changing periods between observing seasons.
The best described object is MWC 342 ( Shevchenko et al. (1993) , Mel'Nikov & Yu (1997) , Chkhikvadze et al. (2002) ). - Dusty clumps may cover the star, e.g., FS CMa itself de Winter & van den Ancker (1997) ).