Phase Curves of Hot Neptune LTT 9779b Suggest a High-metallicity Atmosphere
Name
Crossfield_2020_ApJL_903_L7.pdf
Description
Published version
Size
8.43 MB
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Checksum (MD5)
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Author(s)
Crossfield, Ian JM
Dragomir, Diana
Cowan, Nicolas B
Daylan, Tansu
Wong, Ian
Kataria, Tiffany
Deming, Drake
Kreidberg, Laura
Mikal-Evans, Thomas
Gorjian, Varoujan
Date Issued
2020
Journal
Astrophysical Journal Letters
Publisher
American Astronomical Society
Version
Final published version
Abstract
Phase-curve measurements provide a global view of the composition, thermal structure, and dynamics of exoplanet atmospheres. Although most of the dozens of phase-curve measurements made to date are of large, massive hot Jupiters, there is considerable interest in probing the atmospheres of the smaller planets that are the more typical endproduct of the planet formation process. One such planet that is favorable for these studies is the ultrahot Neptune LTT 9779b, a rare denizen of the Neptune desert. A companion paper presents the planet’s secondary eclipses and dayside thermal emission spectrum; in this work we describe the planet’s optical and infrared phase curves, characterized using a combination of Spitzer and Transiting Exoplanet Survey Satellite (TESS) photometry. We detect LTT 9779b’s thermal phase variations at 4.5 μm, finding a phase amplitude of 358 ± 106 ppm and no significant phase offset, with a longitude of peak emission occurring −10° ± 21° east of the substellar point. Combined with our secondary eclipse observations, these phase-curve measurements imply a 4.5 μm dayside brightness temperature of 1800 ± 120 K, a nightside brightness temperature of 700 ± 430 K (<1350 K at 2σ confidence), and a day–night brightness temperature contrast of 1110 ± 460 K. We compare our data to the predictions of 3D general circulation models calculated at multiple metallicity levels and to similar observations of hot Jupiters experiencing similar levels of stellar irradiation. Though not conclusive, our measurement of its small 4.5 μm phase offset, the relatively large amplitude of the phase variation, and the qualitative differences between our target’s dayside emission spectrum and those of hot Jupiters of similar temperatures all suggest a supersolar atmospheric metallicity for LTT 9779b, as might be expected given its size and mass. Finally, we measure the planet’s transits at both 3.6 μm and 4.5 μm, providing a refined ephemeris (P = 0.79207022 ± 0.00000069 days, T = 2458783.51636 ± 0.00027, BJD ) that will enable efficient scheduling of future observations to further characterize the atmosphere of this intriguing planet. 0 TDB
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics
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DOI of Published Version
https://doi.org/10.3847/2041-8213/ABBC71
