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dc.contributor.authorHardegree-Ullman, K.K.
dc.contributor.authorChristiansen, J.L.
dc.contributor.authorCiardi, D.R.
dc.contributor.authorCrossfield, I.J.M.
dc.contributor.authorDressing, C.D.
dc.contributor.authorLivingston, J.H.
dc.contributor.authorVolk, K.
dc.contributor.authorAgol, E.
dc.contributor.authorBarclay, T.
dc.contributor.authorBarentsen, G.
dc.contributor.authorBenneke, B.
dc.contributor.authorGorjian, V.
dc.contributor.authorKristiansen, M.H.
dc.date.accessioned2021-07-20T00:11:03Z
dc.date.available2021-07-20T00:11:03Z
dc.date.issued2021
dc.identifier.citationHardegree-Ullman, K. K., Christiansen, J. L., Ciardi, D. R., Crossfield, I. J. M., Dressing, C. D., Livingston, J. H., Volk, K., Agol, E., Barclay, T., Barentsen, G., Benneke, B., Gorjian, V., & Kristiansen, M. H. (2021). K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System. Astronomical Journal, 161(5).
dc.identifier.issn0004-6256
dc.identifier.doi10.3847/1538-3881/abeab0
dc.identifier.urihttp://hdl.handle.net/10150/660797
dc.description.abstractK2 greatly extended Kepler's ability to find new planets, but it was typically limited to identifying transiting planets with orbital periods below 40 days. While analyzing K2 data through the Exoplanet Explorers project, citizen scientists helped discover one super-Earth and four sub-Neptune sized planets in the relatively bright (V = 12.21, K = 10.3) K2-138 system, all which orbit near 3:2 mean-motion resonances. The K2 light curve showed two additional transit events consistent with a sixth planet. Using Spitzer photometry, we validate the sixth planet's orbital period of 41.966 ± 0.006 days and measure a radius of 3.44_-0.31 +0.32, R, solidifying K2-138 as the K2 system with the most currently known planets. There is a sizeable gap between the outer two planets, since the fifth planet in the system, K2-138 f, orbits at 12.76 days. We explore the possibility of additional nontransiting planets in the gap between f and g. Due to the relative brightness of the K2-138 host star, and the near resonance of the inner planets, K2-138 could be a key benchmark system for both radial velocity and transit-timing variation mass measurements, and indeed radial velocity masses for the inner four planets have already been obtained. With its five sub-Neptunes and one super-Earth, the K2-138 system provides a unique test bed for comparative atmospheric studies of warm to temperate planets of similar size, dynamical studies of near-resonant planets, and models of planet formation and migration. © 2021. The American Astronomical Society. All rights reserved.
dc.language.isoen
dc.publisherAmerican Astronomical Society
dc.rightsCopyright © 2021. The American Astronomical Society. All rights reserved.
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.titleK2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System
dc.typeArticle
dc.typetext
dc.contributor.departmentLunar and Planetary Laboratory, The University of Arizona
dc.identifier.journalAstronomical Journal
dc.description.noteImmediate access
dc.description.collectioninformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.
dc.eprint.versionFinal published version
dc.source.journaltitleAstronomical Journal
refterms.dateFOA2021-07-20T00:11:03Z


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