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Loose Ends for the Exomoon Candidate Host Kepler-1625b

Teachey, Alex and Kipping, David and Burke, Christopher J. and Angus, Ruth and Howard, Andrew W. (2020) Loose Ends for the Exomoon Candidate Host Kepler-1625b. Astronomical Journal, 159 (4). Art. No. 142. ISSN 1538-3881. https://resolver.caltech.edu/CaltechAUTHORS:20190515-093359054

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Abstract

The claim of an exomoon candidate in the Kepler-1625b system has generated substantial discussion regarding possible alternative explanations for the purported signal. In this work, we examine these possibilities in detail. First, the effect of more flexible trend models is explored, and we show that sufficiently flexible models are capable of attenuating the signal—although this is an expected byproduct of invoking such models. We also explore trend models using x- and y-centroid positions, and show that there is no data-driven impetus to adopt such models over temporal ones. We quantify the probability that the 500 ppm moon-like dip could be caused by a Neptune-sized transiting planet to be <0.75%. We show that neither autocorrelation, Gaussian processes, nor a Lomb–Scargle periodogram are able to recover a stellar rotation period, demonstrating that K1625 is a quiet star with periodic behavior <200 ppm. Through injection and recovery tests, we find that the star does not exhibit a tendency to introduce false-positive dip-like features above that of pure Gaussian noise. Finally, we address a recent reanalysis by Kreidberg et al. and show that the difference in conclusions is not from differing systematics models but rather the reduction itself. We show that their reduction exhibits, in comparison to the original analysis: (i) slightly higher intraorbit and post-fit residual scatter, (ii) ≃900 ppm larger flux offset at the visit change, (iii) ≃2 times larger y-centroid variations, and (iv) ≃3.5 times stronger flux-centroid correlation coefficient. These points could be explained by larger systematics in their reduction, potentially impacting their conclusions.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-3881/ab7001DOIArticle
https://arxiv.org/abs/1904.11896arXivDiscussion Paper
ORCID:
AuthorORCID
Teachey, Alex0000-0003-2331-5606
Kipping, David0000-0002-4365-7366
Burke, Christopher J.0000-0002-7754-9486
Angus, Ruth0000-0003-4540-5661
Howard, Andrew W.0000-0001-8638-0320
Additional Information:© 2020 The American Astronomical Society. Received 2019 April 30; revised 2019 December 9; accepted 2020 January 23; published 2020 March 5. We would like to thank Laura Kreidberg for useful discussions and providing data products in advance of her paper, which allowed us to investigate in greater detail the source and degree of the discrepancies between her findings and ours. We also thank Erik Petigura for performing the v sin i measurement. We thank the anonymous reviewer for thorough comments, which strengthened this paper. Finally, we wish to thank past and present HST and Kepler scientists and engineers, mission support personnel, and the crews of STS-31, 61, 82, 103, 109, and 125, who through their dedication have been jointly responsible for making this work possible. Analysis was carried out in part on the NASA Supercomputer PLEIADES (Grant #HEC-SMD-17-1386). A.T. is supported through the NSF Graduate Research Fellowship (DGE-1644869). D.K. is supported by the Alfred P. Sloan Foundation Fellowship. This work is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #GO-15149. Support for program #GO-15149 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555." This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate.
Group:Astronomy Department
Funders:
Funding AgencyGrant Number
NASAHEC-SMD-17-1386
NSF Graduate Research FellowshipDGE-1644869
Alfred P. Sloan FoundationUNSPECIFIED
NASANAS 5-26555
Subject Keywords:Planetary Systems ; planets and satellites: detection; Natural satellites Extrasolar ; Irregular natural satellites Extrasolar
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: Natural satellites (Extrasolar) (483); Irregular natural satellites (Extrasolar) (2025); Exoplanet detection methods (489)
Record Number:CaltechAUTHORS:20190515-093359054
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190515-093359054
Official Citation:Alex Teachey et al 2020 AJ 159 142
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95505
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 May 2019 02:33
Last Modified:09 Apr 2020 17:20

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