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     Kepler KOI-2442 (Kepler-386; KIC-11080405) 4-(or more?)-Planet System

Discussion:
For the closer-in planet, KOI-2442.02 (Kepler-386b), (O-C) vs. Time data did not show any credible periodicity in its LSP.
However, with regard to KOI-2442.01 (Kepler-386c), after a sinusoidal curve-fit of the (O-C) vs. Time data showed (Figure 1. below) a periodicity (P_ttv) of 404.36 ± 13.71 days (400.52 days was observed in the Lomb-Scargle Periodogram (LSP) of the same data), a plot (Figure 2.) of the Residuals also gave a good sinusoidal curve-fit with a periodicity of 659.02 ± 49.73 days (LSP: 659.71 days).  The added combination of these two sinusoidal curves, arrayed in Figure 3. produces a complex overall curvature reasonably consistent with the initial data.
While it is certainly possible (see recent work of Lithwick and others) that some of the unusual curvature for 2442.01 obtains from eccentric orbits (and maybe even precessing eccentric orbits) of planetary objects in this system, it is also possible that at least 4 planets, two transiting and two not, in near-circular orbits are mutually-interacting to give the TTV distributions observed.

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 1.: KOI-2442.02, P = 12.31 days [Plot avg. error bars = ± 11.40 min.]
[Lomb-Scargle periodogram did show a periodicity of 1227.52 days but it had an FAP of 0.800.]
Linear ephemeris (this work): Tc = [12.31025564 ± 0.00010008](Tc#) + [74.87219801 ± 0.00707728]

Figure 2.: KOI-2442.01, P = 25.19 days [Plot avg. error bars = ± 13.95 min.]
TTV_minimum: 246.32 ± 30.02 days, Amp_ttv_minimum: -26.84 ± 7.63 min.
TTV_maximum: 448.50 ± 32.59 days, Amp_ttv_maximum: 27.86 ± 7.63 min.
TTV_minimum: 650.68 ± 36.30 days, Amp_ttv_minimum: -26.84 ± 7.63 min.
TTV_maximum: 852.86 ± 40.83 days, Amp_ttv_maximum: 27.86 ± 7.63 min.
TTV_minimum: 1055.04 ± 45.94 days, Amp_ttv_minimum: -26.84 ± 7.63 min.
TTV_maximum: 1257.22 ± 51.46 days, Amp_ttv_maximum: 27.86 ± 7.63 min.
TTV_minimum: 1459.40 ± 57.26 days, Amp_ttv_minimum: -26.84 ± 7.63 min.
P_ttv: 404.36 ± 13.71 days.
Amp_ttv: 54.70 ± 10.80 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 400.52 days; Power: 6.70; FAP: 0.0146.
Linear ephemeris (this work): Tc = [25.19342839 ± 0.00022495](Tc#) + [79.42413640 ± 0.00718736]


Figure 3.: Residuals of Figure 2. [Plot avg. error bars = ± 15.90 min.]
TTV_minimum: 369.35 ± 72.22 days, Amp_ttv_minimum: -19.35 ± 6.70 min.
TTV_maximum: 698.86 ± 84.97 days, Amp_ttv_maximum: 16.96 ± 6.70 min.
TTV_minimum: 1028.37 ± 102.28 days, Amp_ttv_minimum: -19.35 ± 6.70 min.
TTV_maximum: 1357.88 ± 122.22 days, Amp_ttv_maximum: 16.96 ± 6.70 min.
P_ttv: 659.02 ± 49.73 days.
Amp_ttv: 36.31 ± 9.47 minutes.
Lomb-Scargle periodogram, candidate P_ttv: 659.71 days; Power: 4.58; FAP: 0.140.


Figure 4.: Added combination of Figures 2., and 3. [Plot error bars = ± 21.15 min.]


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

18 April 2015