TY - JOUR
T1 - An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Subsolar Water Abundance
AU - Colón, Knicole D.
AU - Kreidberg, Laura
AU - Welbanks, Luis
AU - Line, Michael R.
AU - Madhusudhan, Nikku
AU - Beatty, Thomas
AU - Tamburo, Patrick
AU - Stevenson, Kevin B.
AU - Mandell, Avi
AU - Rodriguez, Joseph E.
AU - Barclay, Thomas
AU - Lopez, Eric D.
AU - Stassun, Keivan G.
AU - Angerhausen, Daniel
AU - Fortney, Jonathan J.
AU - James, David J.
AU - Pepper, Joshua
AU - Ahlers, John P.
AU - Plavchan, Peter
AU - Awiphan, Supachai
AU - Kotnik, Cliff
AU - Mcleod, Kim K.
AU - Murawski, Gabriel
AU - Chotani, Heena
AU - Lebrun, Danny
AU - Matzko, William
AU - Rea, David
AU - Vidaurri, Monica
AU - Webster, Scott
AU - Williams, James K.
AU - Cox, Leafia Sheraden
AU - Tan, Nicole
AU - Gilbert, Emily A.
N1 - Publisher Copyright:
© 2020. The American Astronomical Society. All rights reserved..
PY - 2020/12
Y1 - 2020/12
N2 - We present an optical-to-infrared transmission spectrum of the inflated sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic grism, and the Spitzer Space Telescope (Spitzer) at 3.6 μm, in addition to a Spitzer 4.5 μm secondary eclipse. The precise HST transmission spectrum notably reveals a low-amplitude water feature with an unusual shape. Based on free-retrieval analyses with varying molecular abundances, we find strong evidence for water absorption. Depending on model assumptions, we also find tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water abundance is generally ≲0.1 solar (0.001-0.7 solar over a range of model assumptions), several orders of magnitude lower than expected from planet formation models based on the solar system metallicity trend. We also consider chemical-equilibrium and self-consistent 1D radiative-convective equilibrium model fits and find that they, too, prefer low metallicities ([M/H] ≲ -2, consistent with the free-retrieval results). However, all of the retrievals should be interpreted with some caution because they either require additional absorbers that are far out of chemical equilibrium to explain the shape of the spectrum or are simply poor fits to the data. Finally, we find that the Spitzer secondary eclipse is indicative of full heat redistribution from KELT-11b's dayside to nightside, assuming a clear dayside. These potentially unusual results for KELT-11b's composition are suggestive of new challenges on the horizon for atmosphere and formation models in the face of increasingly precise measurements of exoplanet spectra.
AB - We present an optical-to-infrared transmission spectrum of the inflated sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic grism, and the Spitzer Space Telescope (Spitzer) at 3.6 μm, in addition to a Spitzer 4.5 μm secondary eclipse. The precise HST transmission spectrum notably reveals a low-amplitude water feature with an unusual shape. Based on free-retrieval analyses with varying molecular abundances, we find strong evidence for water absorption. Depending on model assumptions, we also find tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water abundance is generally ≲0.1 solar (0.001-0.7 solar over a range of model assumptions), several orders of magnitude lower than expected from planet formation models based on the solar system metallicity trend. We also consider chemical-equilibrium and self-consistent 1D radiative-convective equilibrium model fits and find that they, too, prefer low metallicities ([M/H] ≲ -2, consistent with the free-retrieval results). However, all of the retrievals should be interpreted with some caution because they either require additional absorbers that are far out of chemical equilibrium to explain the shape of the spectrum or are simply poor fits to the data. Finally, we find that the Spitzer secondary eclipse is indicative of full heat redistribution from KELT-11b's dayside to nightside, assuming a clear dayside. These potentially unusual results for KELT-11b's composition are suggestive of new challenges on the horizon for atmosphere and formation models in the face of increasingly precise measurements of exoplanet spectra.
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U2 - 10.3847/1538-3881/abc1e9
DO - 10.3847/1538-3881/abc1e9
M3 - Article
AN - SCOPUS:85106134970
SN - 0004-6256
VL - 160
JO - Astronomical Journal
JF - Astronomical Journal
IS - 6
M1 - 280
ER -