The emission-line features may be intrinsically absent or simply swamped by the additional variable component: in the latter case, emission lines may become visible when the variable component is at a low level.
In the latter case, emission lines may become visible when the variable component is at a low level. The emission-line features may be intrinsically absent or simply swamped by the additional variable component.
The emission-line features may be intrinsically absent or simply swamped by the additional variable component. In the latter case, emission lines may become visible when the variable component is at a low level.
The emission-line features may be intrinsically absent or simply swamped by the additional variable component. In the latter case, emission lines may become visible when the variable component is at a low level.