If the orbital velocity is a constant (in this case 153 km/s), the orbit of each star about the center of mass must be circular. You need to specify which of the stars has an orbital velocity of 153 km/s. Unless the stars have equal mass, they will move at different velocities about the center of mass, and at different distances.
Most eclipsing binaries are not in highly circular orbits. Just because the veolcity of one star in its orbit is 153 km/s at one particular time does not mean it will remain that value.
In a problem like this, for circular orbits, you can use the Newton form of Kepler's third law, if R is the distance between the two stars and M is the combined mass. That is how you should proceed.
If this confuses you, it is explained much better at
http://www.astro.cornell.edu/academics/courses/astro2201/kepler_binary.htm
If an eclipsing binary system has a period of 32 days, an orbital velocity of 153km/s, and an orbit that is nearly edge-on, what is the circumference of the orbit? The radius of the orbit? The mass of the system?
I can't seem to find a starting point for this problem.
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Oh, yes, yes. This is explained in my book; I just didn't remember this formula or think to apply it to this problem. Thank you so much!
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