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TTVs are derived from Q1-Q16 Kepler data.  x-axes: “Observed Tc” (Mid-Transit Time): EXOFAST’s best-fits from Kepler light flux vs. time data.  y-axes: “(O – C)”: difference between Observed Tc and the Calculated Tc from the graphically obtained linear ephemeris.  The plots are pictured in the order of orbital periods.

Discussion:
Thanks to a recent publication by Ofir, Dreizler et al. (vide infra), the true period of the outermost known planet in this system, KOI-1574.02, has been revealed as ~ 191.23 days.   Due to data gaps and the ultimate duration of the 3-gyroscope-stable-Kepler observations, only 4 transits of this planet were recorded.  Through Q16,  as seen in the above plots, the TTVs of 1574.01 and 1574.02 are either: (a) reasonably well anti-correlated with the small offset seen arising from errors implicit in a 4-point sinusoidal fit, or (b) actually offset because of gravitational effect of other planetary object(s), orbital eccentricities, and/or orbital precessions.  [Potentially, the ground-based "KAFO" project (ref. below) may characterize more transits of either or both 1574.01 and 1574.02 to help illuminate this system's behavior and/or to refine the P_ttv and Amp_ttv's reported below.]  No TTV pattern was noted for KOI-1574.03 or KOI-1574.04, the closest-in planets.

1st Plot: KOI-1574.03, P = 5.83 days [Plot error bars = ± 9.87 min.]
Linear ephemeris (this work): Tc = 5.83351163(Tc#) + 65.65386889

2nd Plot: KOI-1574.04, P = 8.98 days [Plot error bars = ± 10.64 min.]
Linear ephemeris (this work): Tc = 8.97735485(Tc#) + 452.47869332

3rd Plot: KOI-1574.01, P = 114.74 days [Plot error bars = ± 1.92 min.]
TTV_minimum: 374.84 ± 45.71 days, Amp_ttv_minimum: -10.59 ± 2.52 min.
TTV_maximum: 649.54 ± 54.80 days, Amp_ttv_maximum: 11.08 ± 2.52 min.
TTV_minimum: 924.25 ± 66.38 days, Amp_ttv_minimum: -10.59 ± 2.52 min.
TTV_maximum: 1198.96 ± 79.36 days, Amp_ttv_maximum: 11.08 ± 2.52 min.
P_ttv: 549.42 ± 31.30 days.
Amp_ttv: 21.68 ± 3.56 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 544.43 days; Power: 3.73; P-value: 0.0102.
Linear ephemeris (this work): Tc = 114.73659990(Tc#) + 98.15449280

4th Plot: KOI-1574.02, P = 191.23 days [Plot error bars = ± 7.55 min.]
TTV_maximum: ~ 389.42 days, Amp_ttv_maximum: ~ 224.13 min.
TTV_minimum: ~ 620.57 days, Amp_ttv_minimum: ~ -314.48 min.
TTV_maximum: ~ 851.71 days, Amp_ttv_maximum: ~ 224.13 min.
TTV_minimum: ~ 1082.86 days, Amp_ttv_minimum: ~ -314.48 min.
P_ttv: ~ 462.29 days.
Amp_ttv: ~ 538.60 minutes.

Linear ephemeris (this work): Tc = 191.23246056(Tc#) + 219.25330449


References:
• Ofir, Dreizler, Zechmeister, & Husser, 2013, arXiv:1310.2064.
• KAFO Project; Bruce Gary, originator & coordinator; see: http://brucegary.net/kafo/ .
• For Q0-6 TTV data of 1574.01 (thru ~ 563 (BJD-2454900) days), see: Ford et al., 2012, arXiv-1201.1892.
• For Q0-12 TTV data of 1574.01 (thru ~ 1116 (BJD-2454900) days), see: Mazeh et al., 2013, arXiv-1301.5499.

19 Nov 2013
KOI-1574 (Kepler-87, KIC-10028792) 4-(or more?)-Planets