Each of these absorption lines has a characteristic strength that depends on the physical properties of the photosphere.
The Struve–Sahade effect occurs when these lines become anomalously weaker as a star's spectrum is red-shifted, and stronger when it is blue-shifted, most noticeable in the secondary component.
It became important because the effect called into question the values of parameters such as mass and luminosity ratios in massive spectroscopic binary systems.
In 1997, Gies and colleagues provided an alternative explanation, arguing that the collision between the stellar winds from the two stars results in a bow shock that is deflected by the Coriolis force, placing it in an obscuring position along the line of sight to the secondary star.
Other hypotheses have since been created to explain this effect,[5] but models still do not fully reproduce the observed line strengths.