The First Quintuple Star Found with the Kepler K2 Mission
Holger Lehmann (Thueringer Landessternwarte Tautenburg), Saul Rappaport (Department of Physics and Kavli Institute for Astrophysics and Space Science Research, MIT, Cambridge, USA), Belinda Kalomeni (Department of Astronomy and Space Science, Ege University, Izmir, Turkey), Tamas Borkovits (Baja Astronomical Observatory of Szeged University, Hungary)

We report on a quintuple star system found with the Kepler K2 mission. Its unusual architecture includes two stellar images separated by 11 arcsec on the sky. Our investigation is based on the analysis of the Kepler light curve complemented by adaptive optics (AO), speckle imaging, and radial velocity (RV) studies. It reveals that one image actually hosts two eclipsing binaries, 'A' and 'B', which are resolved within that image at 0.09 arcsec, while the other one appears to be single. The 'A' binary is circular with a 5.1-day period, while the 'B' binary is eccentric with a 13.1-day period. Spectral analysis together with Monte Carlo simulations based on the derived mass functions and observed relative fluxes allow us to place all stars into the Teff-log(g) diagram and to compare their positions with theoretic evolutionary tracks. Based on the derived difference in the systemic velocities of the two binaries and their projected separation, we derive most likely values for the period and separation of the orbit of the two binaries revolving about each other. The results show that motion within this orbit should be discernible via future RV, AO, and speckle imaging studies within a couple of years. The very small difference in RV and proper motion between the two binaries and the single object implies that all these objects are physically bound, making this at least a quintuple star system.