Most of the movies are available in one or more of the following three formats: QuickTime, MPEG, and animated GIF. QT viewers are readily available as plug-in options for common PC and Mac browsers (e.g., Netscape and Internet Explorer). MPEG is the de facto standard in the Unix world (although Unix users should note that the latest versions of "xanim" support QT movies). Animated GIFs may be viewed using most browsers, and with the xanim tool on Unix boxes. In most cases, the animated GIF versions are reduced in size and length to facilitate easy downloads for slow connections.
In the first half of the movie, the parallax motion of the red star over the course of one year is shown. Note that the star is not moving through space, as can be seen in the bottom panel, only the Earth is moving. The star's parallax motion is simply a reflection of the Earth's orbital motion. When viewed from the moving Earth (top panel), the red star appears to move first west (towards the right) then east (towards the left) with respect to the distant background stars which are so far away that their parallax motions are too small to be seen at this scale.
In the second half, we move the star 2x farther away (as indicated by the scale bar at the bottom) and run through another year. Now the annual the trigonometric parallax motions are 2x smaller because the distance to the star is 2x greater. This fact, that the trigonometric parallax of a star is inversely proportional to its distance from the Sun gives us a direct measurement of the star's distance.
Note that the parallax motion of the star is an illusion due to the orbital motion of the Earth around the Sun. Real stars are much more distant than shown here. For example, one of the nearest stars, Alpha Centauri, is about 277,000 AU away, resulting in a parallax of about 0.74 arcseconds.
[Credit: R. Pogge, OSU]
[Details]
[Credit: R. Pogge, OSU]
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The first movie shows the two stars in circular orbits about their center of mass (marked with the green dot). Two orbits are shown, with the orbit traced as a white line. Both stars move at a uniform speed around the center of mass, the more massive, blueish F0v star moves less as it is closer to the center-of-mass than the less massive, reddish M0v star.
The second movie shows the two stars in elliptical orbits about their center of mass, with an orbital eccentricity of 0.4. Watch how both stars noticeably speed up and slow down as they pass periastron (closest approach to the C-of-M) and apastron (farthest from C-of-M), respectively, thus obeying Kepler's Second Law (equal areas in equal times) the same as the planets in the Solar System.
[Credit: R. Pogge, OSU]
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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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Notice that the deepest eclipse occurs when the secondary is in front of the primary. This is because of the nearly factor of two greater effective temperature of the primary (10,000K compared to 5,500K). Since surface brightness scales like T4, more light is blocked when the secondary is blocking part of the primary, than when the primary completely blocks the secondary.
[Credit: R. Pogge, OSU]
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