Color range from blue for largest blueshift to white for zero Doppler shift to red for largest redshift. For the sake of argument we shall consider a spherically-symmetric optically thin envelope which is radially expanding away from the stellar photosphere. This prevents the observer from seeing the maximum of the redshifted emission line component. The blueward edge of the absorption line often has a much larger absolute Doppler shift than the redward edge of the emission line. It is from the absorption feature that the maximum expansion velocity is determined.
Colors have same meaning as previous diagram.
Right figure is the case of a wind decelerating due to gravity, it is barely able to escape the gravitational pull of the star. These spectral signatures of rapid plasma ejection indicate that there is a relationship between quasars and stars with extended atmospheres and strong stellar winds. Large amounts of dust naturally collect in the circumstellar shell of laser stars. Some of the dust may reach escape velocity and leave the shell, but this is replaced by condensation from recent plasma ejections. Therefore there should be an ample supply of colder gas and dust to aid in the rapid plasma cooling.