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TTVs are derived from Q0-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-227.01, P = 17.69 days [Plot avg. error bars = ± 2.94 min. (smaller than symbols)]
TTV_minimum: 382.75 ± 14.23 days, Amp_ttv_minimum: -517.59 ± 30.41 min.
TTV_maximum: 943.10 ± 19.62 days, Amp_ttv_maximum: 677.76 ± 30.41 min.
P_ttv: 1120.70 ± 17.56 days.
Amp_ttv: 1195.35 ± 43.01 minutes.
Lomb-Scargle periodogram, periodicity (P_ttv): 1104.23 days; Power: 25.95; FAP: 3.254 x 10^-9.
Linear ephemeris (this work): Tc = 17.68898894(Tc#) + 69.46964887

Literature: Tc#, Tc, and TTV Major Tabulations and Other References (also see "Summary" page):
• Nesvorny, Kipping, & Terrell, arXiv-1405.2060, 8 May 2014.
• For Q0-6 TTV data (thru ~ 563 (BJD-2454900) days): Ford et al., 2012, arXiv-1201.1892.
• For Q0-10 TTV data (thru ~ 934 (BJD-2454900) days): Rowe et al., 2014, arXiv-1402.6534.
• For Q0-12 TTV data (thru ~ 1116 (BJD-2454900) days): Mazeh et al., 2013, arXiv-1301.5499.
• For Q0-12 Calc. properties from TTVs: Hadden & Lithwick, 2013, arXiv-1310.7942.
• For Q0-13/14 TTV data, Xie: http://www.astro.utoronto.ca/~jwxie/TTV/TTV_Home.html
• Two ground-based Kepler-TTV-follow-up programs are in place at the moment: --- Gary, "KAFO" project: http://brucegary.net/kafo/ --- von Essen, "KOINet": http://koinet.astro.physik.uni-goettingen.de/

21 May 2014
Kepler KOI-227.01 (KIC-6185476) 2-(or more?)-Planet System

TTV Evidence:
The presence of both a credible (i.e.: False Alarm Probability (FAP) < 0.1) periodicity in the Lomb-Scargle Periodogram (LSP) of [(O-C) vs. Time] ("TTVxy") data points, along with a sinusoidal distribution of the same points displaying a corresponding periodicity ("P_ttv") (see Figure(s) below), is strongly suggestive of the presence of an unseen (non-transiting), gravitationally perturbing planetary object(s) in the system.