Kepler-432: A Red Giant Interacting with One of its Two Long-period Giant Planets

Creators: Quinn, Samuel N.; Ciardi, David R.

Abstract

We report the discovery of Kepler-432b, a giant planet (M_b = 5.41^(+0.32)_(-0.18)M_Jup, R_b = 1.145^(+0.036)_(-0.039)R_Jup) transiting an evolved star (M_* = 1.32^(+0.10)_(-0.07)M_⊙, R_* = 4.06^(+0.12)_(-0.08)R_⊙) with an orbital period of P_b = 52.501129^(+0.000067)_(-0.000053) days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of e=0.5134^(+0.0098)_(-0.0089), which we also measure independently with asterodensity profiling (AP; e=0.507^(+0.039)_(-0.114)), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; M_c sin i_c = 2.43^(+0.22)_(-0.24) M_Jup, P_c = 406.2^(+3.9)_(-2.5) days), and adaptive optics imaging revealed a nearby (0".87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise ratio asteroseismic oscillations, which enable precise measurements of the stellar mass, radius, and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5 day orbit may have been shaped by star–planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU.

Additional Information

© 2015 The American Astronomical Society. Received 2014 October 27; accepted 2015 January 24; published 2015 April 14. We thank Russel White and an anonymous referee for valuable discussion and feedback. S.N.Q. is supported by the NSF Graduate Research Fellowship, Grant DGE-1051030. D.W.L. acknowledges partial support from NASA's Kepler mission under Cooperative Agreement NNX11AB99A with the Smithsonian Astrophysical Observatory. D.H. acknowledges support by the Australian Research Council's Discovery Projects funding scheme (project number DEI40101364) and support by NASA under Grant NNX14AB92G issued through the Kepler Participating Scientist Program. M.J.P. gratefully acknowledges the NASA Origins of Solar Systems Program grant NNX13A124G. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (Grant agreement no.: 267864). The research leading to the presented results has also received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no 338251 (StellarAges). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made use of the APASS database, located at the AAVSO Web site. Funding for APASS has been provided by the Robert Martin Ayers Sciences Fund. Facilities: Kepler, FLWO:1.5 m (TRES), NOT (FIES), Keck:II (NIRC2), WIYN (DSSI)

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