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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-854.01, P = 56.06 days [Plot avg. error bars = ± 7.86 min.]
TTV_minimum: 402.63 ± 86.48 days, Amp_ttv_minimum: -10.85 ± 3.91 min.
TTV_maximum: 958.03 ± 121.12 days, Amp_ttv_maximum: 15.23 ± 3.91 min.
P_ttv: 1110.80 ± 108.37 days.
Amp_ttv: 26.08 ± 5.53 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 1087.38 days; Power: 4.87; FAP: 0.0367.
Linear ephemeris (this work): Tc = [56.05611993 ± 0.00026472](Tc#) + [134.16614758 ± 0.00345476]

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

14 Dec 2014
Kepler KOI-854 (KIC-6435936) 2-(or more?)-Planet System

TTV Evidence:
The presence of both a credible periodicity in the Lomb-Scargle Periodogram (LSP) and a corresponding pronounced one (P_ttv) in a sinusoidal distribution of [(O-C) vs. Time] ("TTVxy") data points is strongly suggestive of the presence of a second (possibly unseen, non-transiting) gravitationally-perturbing planetary object in a system.  This is the case for KOI-854.01.