The Peculiar Atmospheric Chemistry of KELT-9b

Kitzmann, Daniel; Heng, Kevin; Rimmer, Paul B.; Hoeijmakers, Jens; Tsai, Shang‐Min; Malik, Matej; Lendl, M.; Deitrick, Russell; Demory, Brice-Olivier

doi:10.3847/1538-4357/aace5a

Cited by 152 publications

(189 citation statements)

References 67 publications

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“…These calculations assume solar elemental abundances (Asplund et al 2009) and include the same species as Harrison et al (2018) plus gaseous, solid, neutral and ionic molecules and atomic forms of Fe, Ti, V, Cr and Mg. Figure 4 shows the equilibrium abundances of several neutral gaseous Fe species between 1000-3000 K at a pressure of 1 mbar nominally corresponding to the optical photosphere. At the equilibrium temperature of WASP-121 b (∼2400 K), neutral atomic Fe is the dominant form of Fe and should therefore be the most easily detected (also see Kitzmann et al 2018;Lothringer et al 2018). We note that the terminator temperature probed in the optical at high resolution, i.e., going as high up in the atmosphere as 1 mbar -1 µbar, can be significantly lower than the equilibrium temperature.…”

Section: Model Spectramentioning

confidence: 83%

“…Some examples include KELT-9 b (Hoeijmakers et al 2018), MASCARA-2 b (Casasayas-Barris et al 2019), WASP-121 b (Evans et al 2017), WASP-33 b (Nugroho et al 2017), WASP-103 b (Cartier et al 2017), and WASP-18 b (Sheppard et al 2017;Arcangeli et al 2018;Espinoza et al 2019). A number of neutral and ionized atomic species have been predicted in the atmospheres of such UHJs (Kitzmann et al 2018;Lothringer et al 2018). In particular, phase-resolved highresolution transmission spectroscopy has proved an excellent way to probe hot Jupiter atmospheres.…”

Section: Introductionmentioning

confidence: 99%

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Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

Cabot

Madhusudhan

Welbanks

et al. 2020

Monthly Notices of the Royal Astronomical Society

106

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The class of ultra-hot Jupiters comprises giant exoplanets undergoing intense irradiation from their host stars. They have proved to be a particularly interesting population for their orbital and atmospheric properties. One such planet, WASP-121 b, is in a highly misaligned orbit close to its Roche limit, and its atmosphere exhibits a thermal inversion. These properties make WASP-121 b an interesting target for additional atmospheric characterization. In this paper, we present analysis of archival high-resolution optical spectra obtained during transits of WASP-121 b. Artifacts from the Rossiter-McLaughlin effect and Center-to-Limb Variation are deemed negligible. However, we discuss scenarios where these effects warrant more careful treatment by modeling the WASP-121 system and varying its properties. We report a new detection of atmospheric absorption from Hα in the planet with a transit depth of 1.87 ± 0.11%. We further confirm a previous detection of the Na I doublet, and report a new detection of Fe I via cross-correlation with a model template. We attribute the Hα absorption to an extended Hydrogen atmosphere, potentially undergoing escape, and the Fe I to equilibrium chemistry at the planetary photosphere. These detections help to constrain the composition and chemical processes in the atmosphere of WASP-121 b.

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Section: Model Spectramentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

Cabot

Madhusudhan

Welbanks

et al. 2020

Monthly Notices of the Royal Astronomical Society

106

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“…KELT-9b is the hottest known planet, with a dayside temperature of ∼ 4500 K (Gaudi et al 2017). This ultra-hot planet has been shown previously to contain neutral and ionized metals (Hoeijmakers et al 2018(Hoeijmakers et al , 2019, and it is predicted to be heavily influenced by H 2 dissociation/recombination (Bell & Cowan 2018;Komacek & Tan 2018;Kitzmann et al 2018;Lothringer et al 2018). It is also predicted to be too hot for clouds to form, even on the nightside, Figure 1.…”

mentioning

confidence: 82%

“…which simplifies potential interpretations of its phase curve (Kitzmann et al 2018). We describe our observations and data reduction process in Section 2.…”

mentioning

confidence: 99%

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Mansfield

Bean

Stevenson

et al. 2020

ApJL

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121

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Phase curve observations provide an opportunity to study the full energy budgets of exoplanets by quantifying the amount of heat redistributed from their daysides to their nightsides. Theories explaining the properties of phase curves for hot Jupiters have focused on the balance between radiation and dynamics as the primary parameter controlling heat redistribution. However, recent phase curves have shown deviations from the trends that emerge from this theory, which has led to work on additional processes that may affect hot Jupiter energy budgets. One such process, molecular hydrogen dissociation and recombination, can enhance energy redistribution on ultra-hot Jupiters with temperatures above ∼ 2000 K. In order to study the impact of H 2 dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b observed with the Spitzer Space Telescope at 4.5 µm. KELT-9b is the hottest known transiting planet, with a 4.5-µm dayside brightness temperature of 4566 +140 −136 K and a nightside temperature of 2556 +101 −97 K. We observe a phase curve amplitude of 0.609 ± 0.020 and a hot spot offset of 18.7 +2.1 −2.3 • . The observed amplitude is too small to be explained by a simple balance between radiation and advection. General circulation models (GCMs) and an energy balance model that include the effects of H 2 dissociation and recombination provide a better match to the data. The GCMs, however, predict a maximum hot spot offset of 5 • , which disagrees with our observations at > 5σ confidence. This discrepancy may be due to magnetic effects in the planet's highly ionized atmosphere.

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“…Furthermore, this object has been previously studied with high-resolution data in Hoeijmakers et al (2018Hoeijmakers et al ( , 2019. Kitzmann et al (2018) demonstrated that chemical equilibrium is a reasonable assumption, significantly reducing the number of parameters required in the atmospheric model, and that it is cloud-free with a continuum dominated by H − (Arcangeli et al 2018). However, Hoeijmakers et al (2019) suggested that there is most likely missing physics in this model, due to the discrepancy between the expected cross-correlation function for Fe + and the one obtained from the data.…”

Section: Kelt-9bmentioning

confidence: 99%

Interpreting High-resolution Spectroscopy of Exoplanets using Cross-correlations and Supervised Machine Learning

Fisher

Hoeijmakers

Kitzmann

et al. 2020

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We present a new method for performing atmospheric retrieval on ground-based, high-resolution data of exoplanets. Our method combines cross-correlation functions with a random forest, a supervised machine learning technique, to overcome challenges associated with high-resolution data. A series of cross-correlation functions are concatenated to give a "CCF-sequence" for each model atmosphere, which reduces the dimensionality by a factor of ∼ 100. The random forest, trained on our grid of ∼ 65, 000 models, provides a likelihood-free method of retrieval. The pre-computed grid spans 31 values of both temperature and metallicity, and incorporates a realistic noise model. We apply our method to HARPS-N observations of the ultra-hot Jupiter KELT-9b, and obtain a metallicity consistent with solar (log M = −0.2 ± 0.2). Our retrieved transit chord temperature (T = 6000 +0 −200 K) is unreliable as the ion cross-correlations lie outside of the training set, which we interpret as being indicative of missing physics in our atmospheric model. We compare our method to traditional nestedsampling, as well as other machine learning techniques, such as Bayesian neural networks. We demonstrate that the likelihood-free aspect of the random forest makes it more robust than nested-sampling to different error distributions, and that the Bayesian neural network we tested is unable to reproduce complex posteriors. We also address the claim in Cobb et al. (2019) that our random forest retrieval technique can be over-confident but incorrect. We show that this is an artefact of the training set, rather than the machine learning method, and that the posteriors agree with those obtained using nested-sampling.

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The Peculiar Atmospheric Chemistry of KELT-9b

Cited by 152 publications

References 67 publications

Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

Detection of neutral atomic species in the ultra-hot Jupiter WASP-121b

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Interpreting High-resolution Spectroscopy of Exoplanets using Cross-correlations and Supervised Machine Learning

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