CIRCUMBINARY PLANETS ORBITING THE RAPIDLY PULSATING SUBDWARF B-TYPE BINARY NY Vir

摘要

We report here the tentative discovery of a Jovian planet in orbit around the rapidly pulsating subdwarf B-type (sdB-type) eclipsing binary NY Vir. By using newly determined eclipse times together with those collected from the literature, we detect that the observed-calculated (O - C) curve of NY Vir shows a small-amplitude cyclic variation with a period of 7.9 yr and a semiamplitude of 6.1 s, while it undergoes a downward parabolic change (revealing a period decrease at a rate of P = -9.2 x 10~(-12)). The periodic variation was analyzed for the lighttravel-time effect via the presence of a third body. The mass of the tertiary companion was determined to be M_3 sin i' = 2.3(±0.3)M_(Jupiter) when a total mass of 0.60 M_⊙ for NY Vir is adopted. This suggests that it is most probably a giant circumbinary planet orbiting NY Vir at a distance of about 3.3 astronomical units (AU). Since the rate of period decrease cannot be explained by true angular momentum loss caused by gravitational radiation or/and magnetic braking, the observed downward parabolic change in the O - C diagram may be only a part of a long-period (longer than 15 years) cyclic variation, which may reveal the presence of another Jovian planet (～2.5 M_(Jupiter)) in the system.