An independent planet search in theKeplerdataset

Abstract

Context. The primary goal of the Kepler mission is the measurement of the frequency of Earth-like planets around Sun-like stars. However, the confirmation of the smallest of Kepler's candidates in long periods around FGK dwarfs is extremely difficult or even beyond the limit of current radial velocity technology. Transit timing variations (TTVs) may offer the possibility for these confirmations of near-resonant multiple systems by the mutual gravitational interaction of the planets. Aims. We previously detected the second planet candidate in the KOI 1574 system. The two candidates have relatively long periods (about 114 d and 191 d) and are in 5:3 resonance. We therefore searched for TTVs in this particularly promising system. Methods. The full Kepler data was detrended with the proven SARS pipeline. The entire data allowed one to search for TTVs of the above signals, and to search for additional transit-like signals.Results. We detected strong anti-correlated TTVs of the 114 d and 191 d signals, dynamically confirming them as members of the same system. Dynamical simulations reproducing the observed TTVs allowed us to also determine the masses of the planets. We found KOI 1574.01 (hereafter Kepler-87 b) to have a radius of 13.49 ± 0.55 R ⊕ and a mass of 324.2 ± 8.8 M ⊕ , and KOI 1574.02 (Kepler-87 c) to have a radius of 6.14 ± 0.29 R ⊕ and a mass of 6.4 ± 0.8 M ⊕ . Both planets have low densities of 0.729 and 0.152 g cm −3 , respectively, which is non-trivial for such cold and old (7−8 Gyr) planets. Specifically, Kepler-87 c is the lowest-density planet in the super-Earth mass range. Both planets are thus particularly amenable to modeling and planetary structure studies, and also present an interesting case where ground-based photometric follow-up of Kepler planets is very desirable. Finally, we also detected two more short-period super-Earth sized (<2 R ⊕ ) planetary candidates in the system, making the relatively high multiplicity of this system notable against the general paucity of multiple systems in the presence of giant planets like Kepler-87 b.

SOPHIE velocimetry ofKeplertransit candidates

“…Only the EGP at 114 days is within our selection criteria. The two large and long-orbital periods objects have already been confirmed thanks to the transiting timing variation analysis performed by Ofir et al (2014). However, they reported a different period for the outermost planet of 192 d, i.e.…”

“…Finally, from the population of giant and low-mass planets in this M -ρ diagram, five objects do not seem to follow the global trend: Kepler-51 b, c, d (Masuda 2014), Kepler-79 d (JontofHutter et al 2014), and Kepler-87 c (Ofir et al 2014). These planets are very low-mass low-density planets.…”

“…Latham et al 2010;Endl et al 2011;Gandolfi et al 2013) by transit timing variation analyses (e.g. Ofir et al 2014) and by the "multiplicity-boost" validation . Except for a few cases, we did not observe them with SOPHIE, relying on the candidate nature that has been secured in the respective papers.…”

SECURE MASS MEASUREMENTS FROM TRANSIT TIMING: 10 KEPLER EXOPLANETS BETWEEN 3 AND 8 M ⊕ WITH DIVERSE DENSITIES AND INCIDENT FLUXES

“…However, the diminishing likelihood of transiting at longer orbital periods, coupled with the 4yr Kepler baseline, limits the orbital period of planets that have been characterized by transit timing. TTVs have measured planetary masses below 10 M ⊕ with orbital periods ranging from around 7.6 days (Kepler-18 c;Cochranet al 2011) to almost Venus-like distances at 191 days (Kepler-87 c;Ofiret al 2014). TTVs have constrained the masses of nontransiting planets even farther out, e.g., at Kepler-419, which has a likely massive planet beyond 660 days (Dawson et al 2012).…”

“…However, the sensitivity of TTV to low-mass planets beyond the range of RV has enabled the characterization of volatile-rich planets that are far enough from their hosts to have avoided significant mass loss. The precise TTV mass detections to date show a remarkablediversity in planetary density in the mass range from 2 to 8 M ⊕ (Lissauer et al 2011a;Carter et al 2012;Jontof-Hutter et al 2014;Masuda 2014;Ofir et al 2014).…”