Abstrakt
New photometric, spectroscopic, and eclipse timing observations of the eclipsing binary star HP Aur allow for very accurate orbital determinations, even in the presence of a third body and transient starspot activity. The eclipsing binary masses are determined to an accuracy of +-0.4% and the radii to +-0.6%.
The masses are 0.9543 +- 0.0041 and 0.8094 +- 0.0036 solar masses, and the radii are 1.0278 +- 0.0042 and 0.7758 +- 0.0034 solar radii, respectively. The orbital period in the outer orbit is accurately determined for the first time: 4.332 +- 0.011 yr.
A comparison with current theories of stellar evolution shows that the components' absolute properties can be well-matched by the current models at an age of about 7 billion years.