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How X-rays can be used to find the diameters of certain binary stars

In binary star systems, two stars orbit each other. Some of these systems when viewed from Earth exhibit eclipses, as one star passes in front of our line of sight to the other. If we know the orbital velocity and can measure the time the orbiting star spends in front of (or behind) the central star (as is the case in an X-ray binary), we can easily calculate the distance traveled by the secondary as it crosses the diameter of the central star. HT Cas is such a system.

distance as function of time and velocity

Info Tell me more about HT Cas

Info Show me the geometry of the system and the simplifying assumptions
Data Show me an example light curve and a model of orbital periods of binary systems

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