TTVs are derived from Q1-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.
Numerous literature and major Tc#, Tc, and TTV tabulation references can be found on my "Summary" webpage following the table.
16 April 2015
Kepler KOI-2691 (KIC-4552729) 2-(or more?)-Planet System
Discussion: In the example of KOI-2691.01, a sinusoidal curve-fit of the (O-C) vs. Time data showed (Figure below) a periodicity (P_ttv) of 912.11 ± 33.54 days; 903.60 days was observed in the Lomb-Scargle Periodogram (LSP) of the same data).