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. 2018 Oct 3;4(10):eaav1784.
doi: 10.1126/sciadv.aav1784. eCollection 2018 Oct.

Evidence for a large exomoon orbiting Kepler-1625b

Alex Teachey  1 , David M Kipping  1
Affiliations

Evidence for a large exomoon orbiting Kepler-1625b

Alex Teachey et al. Sci Adv. .

Abstract

Exomoons are the natural satellites of planets orbiting stars outside our solar system, of which there are currently no confirmed examples. We present new observations of a candidate exomoon associated with Kepler-1625b using the Hubble Space Telescope to validate or refute the moon's presence. We find evidence in favor of the moon hypothesis, based on timing deviations and a flux decrement from the star consistent with a large transiting exomoon. Self-consistent photodynamical modeling suggests that the planet is likely several Jupiter masses, while the exomoon has a mass and radius similar to Neptune. Since our inference is dominated by a single but highly precise Hubble epoch, we advocate for future monitoring of the system to check model predictions and confirm repetition of the moon-like signal.

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Figures

Fig. 1
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
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
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
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.
See this image and copyright information in PMC

References

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