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KOI's (Blue)  or
K2 Objects (Green)
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-898.03, P = 20.09 days [Plot avg. error bars = ± 8.33 min.]
TTV_maximum: 165.51 ± 24.52 days, Amp_ttv_maximum: 18.76 ± 4.03 min.
TTV_minimum: 355.56 ± 26.00 days, Amp_ttv_minimum: -17.45 ± 4.03 min.
TTV_maximum: 545.62 ± 28.38 days, Amp_ttv_maximum: 18.76 ± 4.03 min.
TTV_minimum: 735.67 ± 31.46 days, Amp_ttv_minimum: -17.45 ± 4.03 min.
TTV_maximum: 925.72 ± 35.05 days, Amp_ttv_maximum: 18.76 ± 4.03 min.
TTV_minimum: 1115.77 ± 39.01 days, Amp_ttv_minimum: -17.45 ± 4.03 min.
TTV_maximum: 1305.82 ± 43.24 days, Amp_ttv_maximum: 18.76 ± 4.03 min.
TTV_minimum: 1495.88 ± 47.67 days, Amp_ttv_minimum: -17.45 ± 4.03 min.
P_ttv: 380.10 ± 10.45 days.
Amp_ttv: 36.21 ± 5.70 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 383.91 days; Power: 10.28; FAP: 0.0191.
Linear ephemeris (this work): Tc = [20.09013838 ± 0.00009614](Tc#) + [80.97997771 ± 0.00399227]


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

25 May 2015
        Kepler KOI-898 (Kepler-83; KIC-7870390) 4-(or more?)-Planet System

Discussion:
A sinusoidal curve-fit of the [(O-C) vs. Time] data for KOI-898.03 (Kepler-83c) showed (Figure below) a periodicity (P_ttv) of 380.10 ± 10.45 days; a Lomb-Scargle Periodogram (LSP) of the same data gave a medium-credibility periodicity of 383.91 days.  Potentially, one other non-transiting planet, perhaps further from the star than KOI-898.03, is gravitationally generating the TTV observed.

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