Detection of a Giant Extrasolar Planet Orbiting the Eclipsing Polar DP Leo

DP Leo is the first discovered eclipsing polar with a short period of 1.4967 hours. The period variation of the eclipsing binary was analyzed by using five new determined eclipse times together with those compiled from the literature. It is discovered that the O - C curve of DP Leo shows a cyclic variation with a period of 23.8 years and a semiamplitude of 31.5 s. The small-amplitude periodic change can be plausibly explained as the light-travel time effect due to the presence of a tertiary companion. The mass of the tertiary component is determined to be M ₃sin i' = 0.00600(±0.00055) M _sun = 6.28(±0.58) M _Jupiter when a total mass of 0.69 M _sun is adopted. If the tertiary companion is coplanar to the eclipsing binary (i.e., i' = 79fdg5), it should be a giant extrasolar planet with a mass of 6.39 M _Jupiter at a distance of 8.6 astronomical units to the central binary. One of the most interesting things that we have learned about extrasolar planets over the last 17 years is that they can exist almost anywhere. The detection of a giant planet orbiting a polar would provide insight into the formation and evolution of circumbinary planets (planets orbiting both components of short-period binaries) as well as the late evolution of binary stars.