HAT-P-13b,c: A TRANSITING HOT JUPITER WITH A MASSIVE OUTER COMPANION ON AN ECCENTRIC ORBIT

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V=10.622 G4 dwarf star GSC 3416-00543 every P = 2.916260±0.000010 days, with transit epoch Tc = 2454779.92979± 0.00038 (BJD) and duration 0.1345± 0.0017d. The outer planet, HAT-P-13c orbits the star with P2 = 428.5±3.0 days and nominal transit center (assuming zero impact parameter) of T2c = 2454870.4± 1.8 (BJD) or time of periastron passage T2,peri = 2454890.05± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22 −0.10M⊙, radius of 1.56± 0.08R⊙, effective temperature 5638± 90K, and is rather metal rich with [Fe/H] = +0.43± 0.08. The inner planetary companion has a mass of 0.851 −0.046MJ, and radius of 1.280±0.079RJ yielding a mean density of 0.499 +0.103 −0.069 g cm . The outer companion has m2 sin i2 = 15.2± 1.0MJ, and orbits on a highly eccentric orbit of e2 = 0.691± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b,c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems. Subject headings: planetary systems — stars: individual (HAT-P-13, GSC 3416-00543) techniques: spectroscopic, photometric