The Near-Contact Binary RU Ursae Minoris

Abstract The near-contact binary RU UMi with an F0-type primary and a K-type secondary was observed in 2003. With the latest version of the Wilson–Devinney code, the photometric elements were computed. The results reveal that RU UMi is a semi-detached system with the secondary component filling its Roche lobe, which should lead to an increase of the period for conservative mass transfer between the two components. However, an orbital period analysis shows that the orbital period of this system undergoes a continuous decrease at a rate of $dP/dt =-1.72 \times 10^{-8} \,\mathrm{d} \,\mathrm{yr}^{-1}$. Therefore, the continuous period decrease may demonstrate that the system is nonconservative. This can result from a combined effect of mass transfer from the secondary component to the primary one and mass and angular momentum loss from the system. With the secular mass and angular momentum losses, RU UMi may evolve from the present short-period near-contact system into an A-type contact binary.