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Exoplanet-Science.com

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.

Figure: KOI-2691.01, P = 97.45 days [Plot avg. error bars = ± 4.53 min.]
TTV_maximum: 556.92 ± 39.42 days, Amp_ttv_maximum: 48.62 ± 4.78 min.
TTV_minimum: 1012.97 ± 50.22 days, Amp_ttv_minimum: -39.67 ± 4.78 min.
P_ttv: 912.11 ± 33.54 days.
Amp_ttv: 88.29 ± 6.76 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 903.60 days; Power: 5.09; FAP: 5.169 x 10^-5.
Linear ephemeris (this work): Tc = [97.44330614 ± 0.00191154](Tc#) + [137.84100502 ± 0.01402519]


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).