KELT-18b: Puffy Planet, Hot Host, Probably Perturbed

June 2017 • 2017AJ....153..263M

Authors • McLeod, Kim K. • Rodriguez, Joseph E. • Oelkers, Ryan J. • Collins, Karen A. • Bieryla, Allyson • Fulton, Benjamin J. • Stassun, Keivan G. • Gaudi, B. Scott • Penev, Kaloyan • Stevens, Daniel J. • Colón, Knicole D. • Pepper, Joshua • Narita, Norio • Tsuguru, Ryu • Fukui, Akihiko • Reed, Phillip A. • Tirrell, Bethany • Visgaitis, Tiffany • Kielkopf, John F. • Cohen, David H. • Jensen, Eric L. N. • Gregorio, Joao • Baştürk, Özgür • Oberst, Thomas E. • Melton, Casey • Kempton, Eliza M. -R. • Baldrige, Andrew • Zhao, Y. Sunny • Zambelli, Roberto • Latham, David W. • Esquerdo, Gilbert A. • Berlind, Perry • Calkins, Michael L. • Howard, Andrew W. • Isaacson, Howard • Weiss, Lauren M. • Benni, Paul • Beatty, Thomas G. • Eastman, Jason D. • Penny, Matthew T. • Siverd, Robert J. • Lund, Michael B. • Labadie-Bartz, Jonathan • Zhou, G. • Curtis, Ivan A. • Joner, Michael D. • Manner, Mark • Relles, Howard • Scarpetta, Gaetano • Stephens, Denise C. • Stockdale, Chris • Tan, T. G. • DePoy, D. L. • Marshall, Jennifer L. • Pogge, Richard W. • Trueblood, Mark • Trueblood, Patricia

Abstract • We report the discovery of KELT-18b, a transiting hot Jupiter in a 2.87-day orbit around the bright (V = 10.1), hot, F4V star BD+60 1538 (TYC 3865-1173-1). We present follow-up photometry, spectroscopy, and adaptive optics imaging that allow a detailed characterization of the system. Our preferred model fits yield a host stellar temperature of 6670+/- 120 K and a mass of {1.524}_-0.068^+0.069 {M}_⊙ , situating it as one of only a handful of known transiting planets with hosts that are as hot, massive, and bright. The planet has a mass of 1.18+/- 0.11 {M}_{{J}}, a radius of {1.570}_-0.036^+0.042 {R}_{{J}}, and a density of 0.377+/- 0.040 {{g}} {{cm}}^-3, making it one of the most inflated planets known around a hot star. We argue that KELT-18b’s high temperature and low surface gravity, which yield an estimated ∼600 km atmospheric scale height, combined with its hot, bright host, make it an excellent candidate for observations aimed at atmospheric characterization. We also present evidence for a bound stellar companion at a projected separation of ∼1100 au, and speculate that it may have contributed to the strong misalignment we suspect between KELT-18's spin axis and its planet’s orbital axis. The inferior conjunction time is 2457542.524998 ± 0.000416 (BJD_TDB) and the orbital period is 2.8717510 ± 0.0000029 days. We encourage Rossiter-McLaughlin measurements in the near future to confirm the suspected spin-orbit misalignment of this system.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2017AJ....153..263M
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/aa6d5d/pdf
• PDF https://stacks.iop.org/1538-3881/153/263/pdf
• PREPRINT http://arxiv.org/abs/1702.01657
• DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?type=REFERENCE&bibcode=2017AJ....153..263M
• DATA https://irsa.ipac.caltech.edu/bibdata/2017/M/2017AJ....153..263M.html
• ELECTR https://doi.org/10.3847%2F1538-3881%2Faa6d5d