|Be shell stars have rotational axis
inclination that provide a line of sight view of their
equatorial region through their decretion disk
material. As such, in some cases, photospheric lines
- H-Balmer and He I - can appear weak or absent entirely
due to a veiling effect by disk material.
Theta CrB is a Be shell star that presently shows little or no indication of a decretion disk, at least in this low resolution spectrum. Rather that of a normal B type star with H-Balmer and He I photospheric absorption lines -- I include it here as a base line example.
Spectrum for 28 Tau shows weak emission at H-alpha, indicating the presence of a decretion disk, with strong absorption lines for both photshpheric and decretion disk material.
Beta Mon A, 59 Cyg and Gamma Cas each show how emission lines in the decretion disk spectrum can 'veil' photosheric absorption lines. In Gamma Cas, H-Balmer absorption lines are entirely absent due to this veiling effect.