Shell star

[1][2] Emission lines are frequently present but not regarded as a defining feature.

The photospheric lines are rotationally broadened showing projected velocities of 200 km/s or more.

[3] The line profiles in shell star spectra are complex, with variable wings, cores, and superpositions of absorption and emission features.

[4] Pleione and Gamma Cassiopeiae itself are both variable stars that have intermittent shell episodes where strong shell features appear in the spectrum and the brightness increases or decreases significantly.

At other times the shell is not detectable in the spectrum, and even the emission lines may disappear.