TTVs are derived from Q0-Q17 Kepler data. x-axes: “Observed Tc” (Mid-Transit Time): EXOFAST’s best-fits from Normalized PDCSAP_FLUX Kepler light flux vs. time (BJD_tdb - 2454900) data. y-axes: “(O-C)”: difference between Observed Tc and the Calculated Tc from the graphically obtained linear ephemeris.
References: • Numerous additional pertinent literature and major Tc#, Tc, and TTV tabulations can be found on my "Summary" webpage following the table.
14 Feb 2015
Kepler KOI-518 (Kepler-174; KIC-8017703) 6(?)-(or more?)-Planet System
Discussion: KOI-518.01, Kepler-174b, the closest-in of the known transiting planets, showed no credible TTVs.
KOI-518.02, Kepler-174c, the middle one of the known transiting planets, showed at least a primary and a secondary one. After a sinusoidal curve-fit of the (O-C) vs. Time data showed (Figure 1.) a periodicity (P_ttv) of 109.38 ± 1.20 days, a plot (Figure 2.) of the Residuals also gave a good sinusoidal curve-fit with a periodicity of 405.31 ± 13.70 days. The added combination of these two sinusoidal curves is arrayed in Figure 3. and reasonably reproduces a complex overall curvature consistent with the initial data. While the sinusoidal behaviors observed could be partially due to orbital eccentricities, it is also possible that 2 additional as yet unseen (probably non-transiting) planets are strongly interacting with 518.02.
KOI-518.03, Kepler-174d, the farthest out known transiting planet, also showed a pronounced periodicity that might be in response to a planet that was also affecting 518.02 or, possibly, due to yet another, still further out, unseen planet: P_ttv: 713.84 ± 21.84 days.