TOI-1518b: A Misaligned Ultra-hot Jupiter with Iron in Its Atmosphere

Creators: Cabot, Samuel H. C.; Bello-Arufe, Aaron; Mendonça, João M.; Tronsgaard, René; Wong, Ian; Zhou, George; Buchhave, Lars A.; Fischer, Debra A.; Stassun, Keivan G.; Antoci, Victoria; Baker, David; Belinski, Alexander A.; Benneke, Björn; Bouma, Luke G.; Christiansen, Jessie L.; Collins, Karen A.; Goliguzova, Maria V.; Hagey, Simone; Jenkins, Jon M.; Jensen, Eric L. N.; Kidwell, Richard C., Jr.; Laloum, Didier; Massey, Bob; McLeod, Kim K.; Latham, David W.; Morgan, Edward H.; Ricker, George; Safonov, Boris S.; Schlieder, Joshua E.; Seager, Sara; Shporer, Avi; Smith, Jeffrey C.; Srdoc, Gregor; Strakhov, Ivan A.; Torres, Guillermo; Twicken, Joseph D.; Vanderspek, Roland; Vezie, Michael; Winn, Joshua N.

Abstract

We present the discovery of TOI-1518b—an ultra-hot Jupiter orbiting a bright star (V = 8.95). The transiting planet is confirmed using high-resolution optical transmission spectra from EXPRES. It is inflated, with R_p = 1.875 ± 0.053 R_J, and exhibits several interesting properties, including a misaligned orbit (240.34^(+0.93)_(−0.98) degrees) and nearly grazing transit (b = 0.9036^(+0.0061)_(−0.0053)). The planet orbits a fast-rotating F0 host star (T_(eff) ≃ 7300 K) in 1.9 days and experiences intense irradiation. Notably, the TESS data show a clear secondary eclipse with a depth of 364 ± 28 ppm and a significant phase-curve signal, from which we obtain a relative day–night planetary flux difference of roughly 320 ppm and a 5.2σ detection of ellipsoidal distortion on the host star. Prompted by recent detections of atomic and ionized species in ultra-hot Jupiter atmospheres, we conduct an atmospheric cross-correlation analysis. We detect neutral iron (5.2σ), at K_p = 157⁺⁶⁸₋₄₄ km s⁻¹ and V_(sys) = −16⁺²₋₄, adding another object to the small sample of highly irradiated gas-giant planets with Fe detections in transmission. Detections so far favor particularly inflated gas giants with radii ≳ 1.78 R_J, which may be due to observational bias. With an equilibrium temperature of T_(eq) = 2492 ± 38 K and a measured dayside brightness temperature of 3237 ± 59 K (assuming zero geometric albedo), TOI-1518b is a promising candidate for future emission spectroscopy to probe for a thermal inversion.

Additional Information

© 2021. The American Astronomical Society. Received 2021 February 16; revised 2021 July 22; accepted 2021 August 5; published 2021 October 27. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. We acknowledge the use of TESS High Level Science Products (HLSP) produced by the Quick-Look Pipeline (QLP) at the TESS Science Office at MIT, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). This work used data from the EXtreme PREcision Spectrograph (EXPRES) that was designed and commissioned at Yale with financial support by the U.S. National Science Foundation under MRI-1429365 and ATI1509436 (PI D. Fischer). We gratefully acknowledge support for telescope time using EXPRES at the LDT from the Heising-Simons Foundation and an anonymous Yale donor. We acknowledge support from U.S. National Science Foundation grant 2009528. This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration et al. 2018). This paper is partially based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. K.K.M. gratefully acknowledges support from the New York Community Trust's Fund for Astrophysical Research. I.W. is supported by a Heising-Simons 51 Pegasi b postdoctoral fellowship. A.A.B., B.S.S., and I.A.S. acknowledge the support of Ministry of Science and Higher Education of the Russian Federation under the grant 075-15-2020-780 (N13.1902.21.0039). This paper is partially based on observations made at the CMO SAI MSU with the support by M.V. Lomonosov Moscow State University Program of Development. V.A. was supported by a research grant (00028173) from VILLUM FONDEN. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). This research made use of exoplanet (Foreman-Mackey et al. 2021) and its dependencies (Astropy Collaboration et al. 2013, 2018; Salvatier et al. 2016; Theano Development Team 2016; Kumar et al. 2019; Luger et al. 2019; Agol et al. 2020). We also acknowledge very useful input from an anonymous referee, which improved the clarity and structure of the manuscript. Software: Tapir (Jensen 2013), AstroImageJ (Collins et al. 2017), molecfit (Smette et al. 2015), radvel (Fulton et al. 2018), Lightkurve (Lightkurve Collaboration et al. 2018), Helios-K (Grimm et al. 2021), FastChem (Stock et al. 2018), batman (Kreidberg 2015), emcee (Foreman-Mackey et al. 2013), SME (Valenti & Piskunov 1996), exoplanet (Foreman-Mackey et al. 2021), astropy (Astropy Collaboration et al. 2018).

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