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Unformatted text preview: companion. Note that this method does not depend on light from the star going in an absolutely straight line as it comes to the observer, and so it works for an observer based on the earth's surface. Note that the Doppler method and the astrometric method allow you to look at two different kinds of orbital motion. Suppose in the same figure the straight path of the star is still in the +y direction, but the wobble is not from side to side, but up and down. (Let there be a z-axis coming up out of the paper, and suppose the wobbly motion is alternating plus z to minus z to plus z, etc. In this kind of motion the star would not be moving closer or further from the observer, and so there would be no Doppler shift. But the observer (at least above the atmosphere) would "see" a wobbly path. Figure 2 shows the same thing from another perspective:...
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- Fall '10