a cubed = p squared. If the period is 8 hours, the a is around 800 thousand miles.
Given a star the size of the sun, that’s only about 350 thousand miles from the surface of the star. circumference of the orbit would be 628,000 miles/hour or 290k m/s. So about a tenth of a percent of the speed of light.
So not quite relativistic...
It's all relative, anyway