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-5231.01, P = 78.88 days [Plot avg. error bars = ± 18.67 min.]
TTV_maximum: 293.52 ± 37.05 days, Amp_ttv_maximum: 56.81 ± 20.24 min.
TTV_minimum: 485.52 ± 39.46 days, Amp_ttv_minimum: -92.75 ± 20.24 min.
TTV_maximum: 677.52 ± 42.80 days, Amp_ttv_maximum: 56.81 ± 20.24 min.
TTV_minimum: 869.52 ± 46.88 days, Amp_ttv_minimum: -92.75 ± 20.24 min.
TTV_maximum: 1061.52 ± 51.51 days, Amp_ttv_maximum: 56.81 ± 20.24 min.
TTV_minimum: 1253.52 ± 56.58 days, Amp_ttv_minimum: -92.75 ± 20.24 min.
TTV_maximum: 1445.52 ± 61.96 days, Amp_ttv_maximum: 56.81 ± 20.24 min.
P_ttv: 384.00 ± 13.47 days.
Amp_ttv: 149.56 ± 28.62 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 391.62 days; Power: 3.70; FAP: 0.0450.
Linear ephemeris (this work): Tc = [78.87424239 ± 0.00253656](Tc#) + [138.13490580 ± 0.02795014]


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

23 May 2015
                 Kepler KOI-5231 (KIC-6045404) 2-(or more?)-Planet System

Discussion:
A sinusoidal curve-fit of the [(O-C) vs. Time] data for KOI-5231.01 showed (Figure below) a periodicity (P_ttv) of 384.00 ± 13.47 days; a Lomb-Scargle Periodogram (LSP) of the same data gave a medium-credibility periodicity of 391.62 days.  Potentially, one other non-transiting planet is gravitationally interacting with KOI-5231.01 in this stellar system.

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