Ole Romer's method still on the stage: the study of two bound eclipsing binaries in quintuple system V994 Her
Abstrakt
More than three hundred years ago, Ole Romer measured the speed of light purely by observing the periodic shift of the observed eclipse arrival times of Jupiter's moons arising from the varying Earth-Jupiter distance. The same method of measuring the periodic modulation of delays is still used in astrophysics.
The ideal laboratories for this effect are eclipsing binaries. The unique system V994 Her consists of two eclipsing binaries orbiting each other.
However, until now it was not certain whether these were gravitationally bound and what their orbital period was. We show that the system is in fact quintuple and the two eclipsing binaries are orbiting each other with a period of about 6.3 yr.
This analysis was performed only through studying the periodic modulation of the two periods: during the periastron passage one binary has an apparently shorter period, while the other one is longer, exactly as required by theory. Additionally, it was found that both inner eclipsing pairs orbit with slightly eccentric orbits, undergoing slow apsidal motion with a period of the order of centuries.