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Finding the Velocity and Period of Cygnus X-1

The following image is a plot of the velocity of Cygnus X-1's optical companion as a function of time. This plot was generated using optical spectral data of the star. The velocity changes over time as the star orbits around Cygnus X-1 - when the velocity is positive it is moving towards us and when it is negative it is moving away from us (XX check this convention). From this plot it is possible to determine the tangential velocity and the period of the optical companion, parameters which can then be used to solve for the mass of Cygnus X-1!

velocity plot of Cygnus X-1's optical companion

Quiz Click here for more information and a quiz on spectra and how this data is collected from spectra.
Return Click here to return to solving for the mass of Cygnus X-1.

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