LARGE ECCENTRICITY, LOW MUTUAL INCLINATION: THE THREE-DIMENSIONAL ARCHITECTURE OF A HIERARCHICAL SYSTEM OF GIANT PLANETS

Abstract

We establish the three-dimensional architecture of the Kepler-419 (previously\nKOI-1474) system to be eccentric yet with a low mutual inclination. Kepler-419b\nis a warm Jupiter at semi-major axis a = 0.370 +0.007/-0.006 AU with a large\neccentricity e=0.85 +0.08/-0.07 measured via the "photoeccentric effect." It\nexhibits transit timing variations induced by the non-transiting Kepler-419c,\nwhich we uniquely constrain to be a moderately eccentric (e=0.184 +/- 0.002),\nhierarchically-separated (a=1.68 +/- 0.03 AU) giant planet (7.3 +/- 0.4 MJup).\nWe combine sixteen quarters of Kepler photometry, radial-velocity (RV)\nmeasurements from the HIgh Resolution Echelle Spectrometer (HIRES) on Keck, and\nimproved stellar parameters that we derive from spectroscopy and\nasteroseismology. From the RVs, we measure the mass of inner planet to be\n2.5+/-0.3MJup and confirm its photometrically-measured eccentricity, refining\nthe value to e=0.83+/-0.01. The RV acceleration is consistent with the\nproperties of the outer planet derived from TTVs. We find that, despite their\nsizable eccentricities, the planets are coplanar to within 9 +8/-6 degrees, and\ntherefore the inner planet's large eccentricity and close-in orbit are unlikely\nto be the result of Kozai migration. Moreover, even over many secular cycles,\nthe inner planet's periapse is most likely never small enough for tidal\ncircularization. Finally, we present and measure a transit time and impact\nparameter from four simultaneous ground-based light curves from 1m-class\ntelescopes, demonstrating the feasibility of ground-based follow-up of Kepler\ngiant planets exhibiting large TTVs.\n