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Spatially resolving the terminator: variation of Fe, temperature, and winds in WASP-76 b across planetary limbs and orbital phase

Gandhi, Siddharth and Kesseli, Aurora and Snellen, Ignas and Brogi, Matteo and Wardenier, Joost P. and Parmentier, Vivien and Welbanks, Luis and Savel, Arjun B. (2022) Spatially resolving the terminator: variation of Fe, temperature, and winds in WASP-76 b across planetary limbs and orbital phase. Monthly Notices of the Royal Astronomical Society, 515 (1). pp. 749-766. ISSN 0035-8711. doi:10.1093/mnras/stac1744.

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Exoplanet atmospheres are inherently three-dimensional systems in which thermal/chemical variation and winds can strongly influence spectra. Recently, the ultra-hot Jupiter WASP-76 b has shown evidence for condensation and asymmetric Fe absorption with time. However, it is currently unclear whether these asymmetries are driven by chemical or thermal differences between the two limbs, as precise constraints on variation in these have remained elusive due to the challenges of modelling these dynamics in a Bayesian framework. To address this, we develop a new model, HyDRA-2D, capable of simultaneously retrieving morning and evening terminators with day-night winds. We explore variations in Fe, temperature profile, winds, and opacity deck with limb and orbital phase using VLT/ESPRESSO observations of WASP-76 b. We find Fe is more prominent on the evening for the last quarter of the transit, with log(X_(Fe)) = −4.03^(+0.28)_(−0.31)⁠, but the morning shows a lower abundance with a wider uncertainty, log(X_(Fe)) = −4.59^(+0.85)_(−1.0)⁠, driven by degeneracy with the opacity deck and the stronger evening signal. We constrain 0.1-mbar temperatures ranging from 2950⁺¹¹¹₋₁₅₆ to 2615⁺²⁶⁶₋₂₇₅ K, with a trend of higher temperatures for the more irradiated atmospheric regions. We also constrain a day-night wind speed of 9.8^(+1.2)_(−1.1) km s⁻¹ for the last quarter, higher than 5.9^(+1.5)_(−1.1) km s⁻¹ for the first, in line with general circulation models. We find our new spatially and phase-resolved treatment is statistically favoured by 4.9σ over traditional 1D-retrievals, and thus demonstrate the power of such modelling for robust constraints with current and future facilities.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gandhi, Siddharth0000-0001-9552-3709
Kesseli, Aurora0000-0002-3239-5989
Snellen, Ignas0000-0003-1624-3667
Brogi, Matteo0000-0002-7704-0153
Wardenier, Joost P.0000-0003-3191-2486
Parmentier, Vivien0000-0001-9521-6258
Welbanks, Luis0000-0003-0156-4564
Savel, Arjun B.0000-0002-2454-768X
Additional Information:© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 25 April 2022. Revision received: 17 June 2022. Accepted: 21 June 2022. Published: 23 June 2022. Corrected and typeset: 19 July 2022. SG is grateful to Leiden Observatory at Leiden University for the award of the Oort Fellowship. This work was performed using the compute resources from the Academic Leiden Interdisciplinary Cluster Environment (ALICE) provided by Leiden University. We also utilize the Avon HPC cluster managed by the Scientific Computing Research Technology Platform (SCRTP) at the University of Warwick. IS acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program under grant agreement No. 694513. MB acknowledges support from from the UK Science and Technology Facilities Council (STFC) research grant ST/T000406/1. JPW sincerely acknowledges support from the Wolfson Harrison UK Research Council Physics Scholarship and the Science and Technology Facilities Council (STFC). LW thanks support provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51496.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. ABS acknowledges support from the Heising-Simons Foundation. We also thank the anonymous referee for a careful review of this paper. DATA AVAILABILITY. The models underlying this paper will be shared on reasonable request to the corresponding author.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Leiden UniversityUNSPECIFIED
European Research Council (ERC)694513
Science and Technology Facilities Council (STFC)ST/T000406/1
Wolfson Harrison UK Research Council Physics ScholarshipUNSPECIFIED
NASA Hubble FellowshipHST-HF2-51496.001-A
Heising-Simons FoundationUNSPECIFIED
Subject Keywords:radiative transfer, methods: numerical, techniques: spectroscopic, planets and satellites: atmospheres, planets and satellites: composition
Issue or Number:1
Record Number:CaltechAUTHORS:20220804-249944000
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Official Citation:Siddharth Gandhi, Aurora Kesseli, Ignas Snellen, Matteo Brogi, Joost P Wardenier, Vivien Parmentier, Luis Welbanks, Arjun B Savel, Spatially resolving the terminator: variation of Fe, temperature, and winds in WASP-76 b across planetary limbs and orbital phase, Monthly Notices of the Royal Astronomical Society, Volume 515, Issue 1, September 2022, Pages 749–766,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116114
Deposited By: George Porter
Deposited On:09 Aug 2022 17:15
Last Modified:09 Aug 2022 17:15

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