Research ArticleASTRONOMY

Evidence for a large exomoon orbiting Kepler-1625b

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Science Advances  03 Oct 2018:
Vol. 4, no. 10, eaav1784
DOI: 10.1126/sciadv.aav1784
  • Fig. 1 Method marginalized detrending.

    Comparison of five different detrending methods on two different Kepler data products (SAP and PDC). The top curve shows the Kepler reduction used in (12), and the bottom curve shows the method marginalized product used in this work. The three panels show the three transits observed by Kepler.

  • Fig. 2 Hook corrections.

    (Top) The optimal aperture photometry of our target (left) and the best comparison star (right), where the hooks and visit-long trends are clearly present. Points are colored by their exposure number within each HST orbit (triangles represent outliers). (Middle) A hook correction using the common exponential ramp model on both stars. (Bottom) The result from an alternative and novel hook correction approach introduced in this work. The intra-orbit root mean square (RMS) value is quoted for the hook-corrected light curves.

  • Fig. 3 HST detrending.

    The HST observations with three proposed trends fit to the data (left) and with the trends removed (right). Bottom-right numbers in each row give the Bayes factor between a planet plus moon model (model M) and a planet plus moon model where the moon radius equals zero (model Z), which tracks the significance of the moon-like dip in isolation.

  • Fig. 4 Moon solutions.

    The three transits in Kepler (top) and the October 2017 transit observed with HST (bottom) for the three trend model solutions. The three colored lines show the corresponding trend model solutions for model M, our favored transit model. The shape of the HST transit differs from that of the Kepler transits owing to limb darkening differences between the bandpasses.

  • Table 1 Model performance.

    Bayesian evidences (Z) and maximum likelihoods (Embedded Image) from our combined fits using Kepler and new HST data. Kepler plus HST fits. The subscripts are P for the planet model, T for the planetary TTV model, Z for the zero-radius moon model, and M for the moon model. The three columns are for each trend model attempted.

    LinearQuadraticExponential
    Embedded Image6302.79 ± 0.116306.68 ± 0.116308.41 ± 0.11
    Embedded Image6304.86 ± 0.116308.81 ± 0.126310.71 ± 0.11
    Embedded Image6306.84 ± 0.116311.12 ± 0.126310.82 ± 0.12
    Embedded Image6315.73 ± 0.126312.92 ± 0.126314.01 ± 0.12
    Embedded Image1.00 ± 0.22*
    Embedded Image25.88 ± 0.3212.47 ± 0.3311.19 ± 0.32
    Embedded Image21.72 ± 0.338.21 ± 0.3417.81 ± 0.33
    Embedded Image17.77 ± 0.333.61 ± 0.336.38 ± 0.34
    Embedded Image18.66*
    Embedded Image54.9341.0441.57
    Embedded Image35.6923.9723.97
    Embedded Image33.6819.5919.22

    *Values derived using the Kepler data in isolation.

    • Table 2 System parameters.

      Median and ±34.1% quantile range of the a posteriori model parameters from model M, where each column defined a different visit-long trend model. The top panel gives the credible intervals for the actual parameters used in the fit, and the lower panel gives a selection of relevant derived parameters conditioned upon our revised stellar parameters. The quoted inclination of the satellite is the inclination modulo 90°.

      ParameterLinearQuadraticExponential
      Photodynamics only
      RP,Kep/REmbedded ImageEmbedded ImageEmbedded Image
      RP,HST/RP,KepEmbedded ImageEmbedded ImageEmbedded Image
      ρ⋆,LC [g cm−3]Embedded ImageEmbedded ImageEmbedded Image
      bEmbedded ImageEmbedded ImageEmbedded Image
      PP [days]Embedded ImageEmbedded ImageEmbedded Image
      τ0 [BJDUTC]Embedded ImageEmbedded ImageEmbedded Image
      q1,KepEmbedded ImageEmbedded ImageEmbedded Image
      q2,KepEmbedded ImageEmbedded ImageEmbedded Image
      q1,HSTEmbedded ImageEmbedded ImageEmbedded Image
      q2,HSTEmbedded ImageEmbedded ImageEmbedded Image
      PS [days]Embedded ImageEmbedded ImageEmbedded Image
      aSP/RPEmbedded ImageEmbedded ImageEmbedded Image
      φS [°]Embedded ImageEmbedded ImageEmbedded Image
      iS [°]Embedded ImageEmbedded ImageEmbedded Image
      ΩS [°]Embedded ImageEmbedded ImageEmbedded Image
      (MS/MP)Embedded ImageEmbedded ImageEmbedded Image
      (RS/RP)Embedded ImageEmbedded ImageEmbedded Image
      Δa0 [ppm]Embedded ImageEmbedded ImageEmbedded Image
      + Stellar properties
      R [R]Embedded ImageEmbedded ImageEmbedded Image
      M [M]Embedded ImageEmbedded ImageEmbedded Image
      ρ⋆,iso [kg m−3]Embedded ImageEmbedded ImageEmbedded Image
      Embedded ImageEmbedded ImageEmbedded ImageEmbedded Image
      RP [R]Embedded ImageEmbedded ImageEmbedded Image
      log10(MP/M)Embedded ImageEmbedded ImageEmbedded Image
      aP [AU]Embedded ImageEmbedded ImageEmbedded Image
      RS [R]Embedded ImageEmbedded ImageEmbedded Image
      log10(MS/M)Embedded ImageEmbedded ImageEmbedded Image
      Seff [S]Embedded ImageEmbedded ImageEmbedded Image
      + forecaster
      log10(MP/M)Embedded ImageEmbedded ImageEmbedded Image
      log10(MS/M)Embedded ImageEmbedded ImageEmbedded Image
      MP [MJ][1.2, 12.5][0.2, 9.0][0.6, 10.5]
      MS [M][4.4, 68][1.0, 140][2.6, 76]
      K [m/s][35, 380][6, 280][18, 320]

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/10/eaav1784/DC1

      Supplementary Materials and Methods

      Fig. S1. The “Phantom” star.

      Fig. S2. Kepler detrending.

      Fig. S3. Kepler detrending comparison.

      Fig. S4. HST image rotation.

      Fig. S5. HST hook model comparison.

      Fig. S6. HST centroids.

      Fig. S7. Spectral analysis.

      Fig. S8. Transmission spectrum.

      Fig. S9. Wavelength solution.

      Fig. S10. Wavelength-dependent pixel sensitivity.

      Fig. S11. Modeling the uncataloged source contamination.

      Fig. S12. Transit timing variations.

      Fig. S13. Residual analysis.

      Fig. S14. Chromatic test.

      Fig. S15. Mass constraints.

      Fig. S16. Model posteriors.

      Fig. S17. Physical posteriors.

      Fig. S18. The May 2019 transit.

      Table S1. Kepler-only fits.

      Table S2. Transmission spectrum.

      Table S3. Transit timings.

      References (4272)

    • Supplementary Materials

      This PDF file includes:

      • Supplementary Materials and Methods
      • Fig. S1. The “Phantom” star.
      • Fig. S2. Kepler detrending.
      • Fig. S3. Kepler detrending comparison.
      • Fig. S4. HST image rotation.
      • Fig. S5. HST hook model comparison.
      • Fig. S6. HST centroids.
      • Fig. S7. Spectral analysis.
      • Fig. S8. Transmission spectrum.
      • Fig. S9. Wavelength solution.
      • Fig. S10. Wavelength-dependent pixel sensitivity.
      • Fig. S11. Modeling the uncataloged source contamination.
      • Fig. S12. Transit timing variations.
      • Fig. S13. Residual analysis.
      • Fig. S14. Chromatic test.
      • Fig. S15. Mass constraints.
      • Fig. S16. Model posteriors.
      • Fig. S17. Physical posteriors.
      • Fig. S18. The May 2019 transit.
      • Table S1. Kepler-only fits.
      • Table S2. Transmission spectrum.
      • Table S3. Transit timings.
      • References (4272)

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