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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.

Figures:
KOI-250.03, P = 3.54 days [Plot avg. error bars = ± 7.46 min.]
Linear ephemeris (this work): Tc = [3.54391522 ± 0.00001025](Tc#) + [69.26063036 ± 0.00237425]

KOI-250.01, P = 12.28 days [Plot avg. error bars = ± 3.10 min.]

TTV_minimum: 353.79 ± 24.66 days, Amp_ttv_minimum: -10.14 ± 1.21 min.
TTV_maximum: 728.31 ± 30.08 days, Amp_ttv_maximum: 11.37 ± 1.21 min.
TTV_minimum: 1102.83 ± 37.51 days, Amp_ttv_minimum: -10.14 ± 1.21 min.
TTV_maximum: 1477.35 ± 45.99 days, Amp_ttv_maximum: 11.37 ± 1.21 min.
P_ttv: 749.04 ± 20.27 days.
Amp_ttv: 21.51 ± 1.71 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 751.75 days; Power: 27.82; FAP: 8.343 x 10^-10.
Linear ephemeris (this work): Tc = [12.28300962 ± 0.00002100](Tc#) + [103.39800860 ± 0.00134551]


KOI-250.02, P = 17.25 days [Plot avg. error bars = ± 4.83 min.]

TTV_maximum: 378.81 ± 38.98 days, Amp_ttv_maximum: 9.12 ± 1.74 min.
TTV_minimum: 743.61 ± 47.51 days, Amp_ttv_minimum: -9.39 ± 1.74 min.
TTV_maximum: 1108.41 ± 58.94 days, Amp_ttv_maximum: 9.12 ± 1.74 min.
TTV_minimum: 1473.21 ± 71.91 days, Amp_ttv_minimum: -9.39 ± 1.74 min.
P_ttv: 729.60 ± 30.97 days.
Amp_ttv: 18.51 ± 2.46 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 738.88 days; Power: 13.12; FAP: 0.00127.
Linear ephemeris (this work): Tc = [17.25121075 ± 0.00003611](Tc#) + [82.88826153 ± 0.00168829]


KOI-250.04, P = 46.83 days [Plot avg. error bars = ± 5.12 min.]

TTV_maximum: 66.79 ± 9.42 days, Amp_ttv_maximum: 6.13 ± 2.29 min.
TTV_minimum: 119.32 ± 9.48 days, Amp_ttv_minimum: -7.64 ± 2.29 min.
TTV_maximum: 171.84 ± 9.57 days, Amp_ttv_maximum: 6.13 ± 2.29 min.
TTV_minimum: 224.37 ± 9.69 days, Amp_ttv_minimum: -7.64 ± 2.29 min.
--- (20 intervening maxima + minima.) ---
TTV_maximum: 1327.45 ± 16.91 days, Amp_ttv_maximum: 6.13 ± 2.29 min.
TTV_minimum: 1379.98 ± 17.37 days, Amp_ttv_minimum: -7.64 ± 2.29 min.
TTV_maximum: 1432.51 ± 17.84 days, Amp_ttv_maximum: 6.13 ± 2.29 min.
TTV_minimum: 1485.04 ± 18.32 days, Amp_ttv_minimum: -7.64 ± 2.29 min.
P_ttv: 105.06 ± 1.11 days.
Amp_ttv: 13.77 ± 3.25 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 104.93 days; Power: 4.29; FAP: 0.099.

Numerous additional (potentially secondary) Lomb-Scargle periodicities with poor FAPs were observed with both long-cadence (LC) and short-cadence (SC) data.  More data points would be needed to determine the validity of any of them:
LC: 182.89 days; Power: 3.04; FAP: 0.465.
SC: 272.94 days; Power: 3.01; FAP: 0.409.
SC: 123.84 days; Power: 3.00; FAP: 0.415.
SC: 203.36 days; Power: 2.32; FAP: 0.719.

Linear ephemeris (this work): Tc = [46.82768176 ± 0.00012677](Tc#) + [69.74454924 ± 0.00216339]

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

11 Feb 2015
        Kepler KOI-250 (Kepler-26; KIC-9757613) 5-(or more?)-Planet System

Discussion:
Not only are TTVs evident for two of the planets in this system, KOI-250.01 and 250.02, but their pronounced anti-correlation evidences their strong gravitational interaction.  This is true even though their period ratio, 1.4045, or about 7/2, is not close to j/(j-1) (where j is an integer) which is typically the case for strongly interacting (and anticorrelated TTV) planets.

Furthermore, within experimental error, the TTV amplitudes for 250.01 and 250.02 and their known (NASA Exoplanet Archive) radii suggest that their masses (and densities) should be virtually the same:
250.01: Amp_ttv: 21.51 ± 1.71; Rp(Rearth): 2.89 ± 0.44;
250.02: Amp_ttv: 18.51 ± 2.46; Rp(Rearth): 2.82 ± 0.43.

The long-cadence data for 250.04 gave a Lomb-Scargle Periodogram showing a periodicity of about 105 days, potentially due to the presence of a fifth (non-transiting) planet, but this was not precisely confirmed using short-cadence data.  Because of its distinctly habitable-zone temperatures (273°K), this planet should be a candidate for future follow-up.