Spectroscopic Binary Stars

Spectroscopic Binary Star

970Kb QuickTime Movie
67Kb MPEG Movie
401Kb Animated GIF

This movie simulates a double-lined spectroscopic binary star system consisting of an F0v primary and M0v secondary in a circular orbit about each other. The orbital plane is oriented along the line of sight in this simulation. The top half of the frame shows the appearance of the two stars seen from above, with the red dot marking the center of mass of the system, and the green dot at left indicating the location of the distant observer. The bottom half of the frame shows the spectrum seen by the distant observer. The absorption lines from the primary star are labeled "A", while those from the secondary star are labeled "B". As the two stars orbit each other, they alternately move towards then away from the observer. This results in their absorption-line spectra getting blue-shifted, then red-shifted, respectively. The pattern of Doppler shifts traces out the orbital motions of each star. A thin "stationary" absorption line appearing between the two lines shows the un-shifted location of each line.

Notice that the primary star's absorption lines (labeled "A") only shift a small amount, reflecting its smaller orbital velocity, compared to that of the secondary, which moves much faster. This because the lower mass secondary star must be located farther from the center-of-mass of the system than the primary, and so has to trace out a much bigger circle in its orbit in the same time that the primary does, making its Doppler shift larger in proportion to their mass ratio.

The amount of Doppler shift seen in this simulation has been greatly exaggerated to make it easily visible.

[Credit: R. Pogge, OSU]
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Prof. Richard Pogge (pogge@astronomy.ohio-state.edu)

Updated: 1998 January 10 [rwp]

Copyright 1998 Richard W. Pogge, All Rights Reserved.