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### The geometry of the eclipsing X-ray binary problem

This diagram illustrates the geometry of the system. The observer, on Earth, views X-rays from the binary system. Most of the X-rays are emitted by the smaller star (whose orbital path is shown in black), which orbits the central star (denoted by a yellow dot in the diagram), but the central star is also a source of some X-rays. If the plane of the binary system is the same as that of the binary system and the observer, then the X-ray emitter can be eclipsed by the central star.

To simplify the problem, we make two assumptions when we use this method:

1. The orbit of the X-ray emitting star is circular and its velocity is constant.

2. The orbit of the observed star is large and the system is distant, so that light rays from the source are parallel.

3. The plane of the binary system is at 90 degrees, edge on to our line of sight. (The actual orbit is at 83 degrees.)
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 Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center. The Imagine Team Acting Project Leader: Dr. Barbara Mattson All material on this site has been created and updated between 1997-2012.