graph
here's that graph. Note the trend that tracks across the graph from about 2 1/2 hours at 0.5 days to 6 1/2 hours at 10 days - it's as if there's a class of objects embedded in there with a very rigid relationship of stellar size to orbital parameters. it could be that this is some sort of stability limit for a binary star system, and that points "above the line" are not typical stars anymore (extended bodies rather than spheres, for instance)