Struve-Sahade effect
Encyclopedia
The Struve-Sahade effect (S-S effect) occurs with a double-lined spectroscopic binary star system. A spectroscopic binary is called double-lined when the absorption lines of both stars can be observed with a spectroscope. As each member of the star system approaches the observer in turn, the absorption lines of that star are shifted toward the blue end of the optical spectrum by the Doppler effect
. Likewise, as a star moves away, its lines are shifted toward the red end of the spectrum. 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.
This effect was first reported by Otto Struve
in 1937. 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 1950, Struve attempted to explain the effect as the result of streams of gas trailing behind the secondary star, causing the star to be obscured when the star was moving away. In 1959, Jorge Sahade produced a model where a gaseous stream extended from the primary to the secondary member of the binary, and the opacity of this stream produced the weakening of the absorption lines. The effect then became known as the Struve-Sahade effect. In 1997, Gies et al. 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.
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
. Likewise, as a star moves away, its lines are shifted toward the red end of the spectrum. Each of these absorption lines has a characteristic strength that depends on the physical properties of the photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...
. The Struve-Sahade effect occurs when these lines become anomalously weaker as a star's spectrum is red-shifted.
This effect was first reported by Otto Struve
Otto Struve
Otto Struve was a Russian astronomer. In Russian, his name is sometimes given as Otto Lyudvigovich Struve ; however, he spent most of his life and his entire scientific career in the United States...
in 1937. 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 1950, Struve attempted to explain the effect as the result of streams of gas trailing behind the secondary star, causing the star to be obscured when the star was moving away. In 1959, Jorge Sahade produced a model where a gaseous stream extended from the primary to the secondary member of the binary, and the opacity of this stream produced the weakening of the absorption lines. The effect then became known as the Struve-Sahade effect. In 1997, Gies et al. 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.