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.
13 April 2015
Kepler KOI-5651 (KIC-9282853) 2-(or more?)-Planet System
Discussion: In the example of KOI-5651.01, a sinusoidal (less than one cycle) curve-fit of the (O-C) vs. Time data showed an approximate periodicity (P_ttv) of ~ 1807.50 days; 1247.79 days was observed in the Lomb-Scargle Periodogram (LSP) of the same data. When less than one cycle of periodicity has been observed by Kepler, the P_ttv values derived from a best-fit sinusoidal curve and the corresponding Lomb-Scargle periodogram can be quite different and show large errors. This is the case for KOI-5651.01 (see plot and data below). Clearly, this can only be remedied by longer-term observations…which may or may not be in the offing via the Kepler K2 project.