KELT-18b: Puffy Planet, Hot Host, Probably Perturbed
Abstract
We report the discovery of KELT-18b, a transiting hot Jupiter in a 2.87d 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+/-0.069 Msun, 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 Mjup, a radius of 1.57+/-0.04 Rjup, 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.
Cite
@article{arxiv.1702.01657,
title = {KELT-18b: Puffy Planet, Hot Host, Probably Perturbed},
author = {Kim K. McLeod and Joseph E. Rodriguez and Ryan J. Oelkers and Karen A. Collins and Allyson Bieryla and Benjamin J. Fulton and Keivan G. Stassun and B. Scott Gaudi and Kaloyan Penev and Daniel J. Stevens and Knicole D. Colón and Joshua Pepper and Norio Narita and Ryu Tsuguru and Akihiko Fukui and Phillip A. Reed and Bethany Tirrell and Tiffany Visgaitis and John F. Kielkopf and David H. Cohen and Eric L. N. Jensen and Joao Gregorio and Özgür Baştürk and Thomas E. Oberst and Casey Melton and Eliza M. -R. Kempton and Andrew Baldridge and Y. Sunny Zhao and Roberto Zambelli and David W. Latham and Gilbert A. Esquerdo and Perry Berlind and Michael L. Calkins and Andrew W. Howard and Howard Isaacson and Lauren M. Weiss and Thomas G. Beatty and Jason D. Eastman and Matthew T. Penny and Robert J. Siverd and Michael B. Lund and Jonathan Labadie-Bartz and G. Zhou and Ivan A. Curtis and Michael D. Joner and Mark Manner and Howard Relles and Gaetano Scarpetta and Denise C. Stephens and Chris Stockdale and T. G. Tan and D. L. DePoy and Jennifer L. Marshall and Richard W. Pogge and Mark Trueblood and Patricia Trueblood},
journal= {arXiv preprint arXiv:1702.01657},
year = {2017}
}
Comments
16 pages, 13 figures, 6 tables, accepted to AJ