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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.

1st Figure., KOI-3791.02, P = 220.13 days [Plot avg. error bars = ± 3.23 min.]
Extrapolated TTV_minimum: 147.08 ± 183.00 days, Amp_ttv_minimum: -8.88 ± 6.33 min.
Observed TTV_maximum: 841.79 ± 244.91 days, Amp_ttv_maximum: 23.49 ± 6.33 min.
Extrapolated TTV_minimum: 1536.49 ± 351.72 days, Amp_ttv_minimum: --8.88 ± 6.33 min.
P_ttv: 1389.41 ± 272.86 days.
Amp_ttv: 32.37 ± 8.95 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 1967.67 days; Power: 1.86; FAP: 0.201 (*).
Linear ephemeris (this work): Tc = 220.12980022(Tc#) + 178.99537319


2nd Figure., KOI-3791.01, P = 440.79 days [Plot avg. error bars = ± 2.21 min.]

TTV_maximum: ~ 186.68 days, Amp_ttv_maximum: ~ 8.17 min.
TTV_minimum: ~ 788.61 days, Amp_ttv_minimum: ~ -13.94 min.
TTV_maximum: ~ 1390.53 days, Amp_ttv_maximum: ~ 8.17 min.
P_ttv: ~ 1203.85 days.
Amp_ttv: ~ 22.12 minutes.
Linear ephemeris (this work): Tc = 440.78415930(Tc#) + 72.35846880


Numerous literature and major Tc#, Tc, and TTV tabulation references can be found on my "Summary" webpage following the table.

6 Oct 2014
                          Kepler KOI-3791 (KIC-5437945) 2-Planet System

Discussion:
When periodicity values from both sinusoidal best-fits of [(O-C) vs. Time] data and Lomb-Scargle Periodograms of the same data are substantial and visually obvious, they may not correspond very closely* if only one cycle of periodicity has been observed.  Further, as in this case, this result can also obtain if very few data points are available*.  An important TTV-confirming observation in this case is that a strong anti-correlation exists (see following figures) between them.