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More Evidence for Variable Helium Absorption from HD 189733b

Zhang, Michael and Cauley, P. Wilson and Knutson, Heather A. and France, Kevin and Kreidberg, Laura and Oklopčić, Antonija and Redfield, Seth and Shkolnik, Evgenya L. (2022) More Evidence for Variable Helium Absorption from HD 189733b. Astronomical Journal, 164 (6). Art. No. 237. ISSN 0004-6256. doi:10.3847/1538-3881/ac9675.

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We present a new Keck/NIRSPEC observation of metastable helium absorption from the upper atmosphere of HD 189733b, a hot Jupiter orbiting a nearby moderately active star. We measure an average helium transit depth of 0.420% ± 0.013% integrated over the [−20, 20] km s⁻¹ velocity range. Comparing this measurement to eight previously published transit observations with different instruments, we find that our depth is 32% (9σ) lower than the average of the three CARMENES transits, but only 16% (4.4σ) lower than the average of the five GIANO transits. We perform 1D hydrodynamical simulations of the outflow, and find that XUV variability on the order of 33%–common for this star–can change the helium absorption depth by up to 60%, although a more typical change is 15%. We conclude that changes in stellar XUV flux can explain the observational variability in helium absorption, but that variability in the stellar He line cannot be excluded. 3D models are necessary to explore other sources of variability, such as shear instability and changing stellar wind conditions.

Item Type:Article
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URLURL TypeDescription ItemDiscussion Paper
Zhang, Michael0000-0002-0659-1783
Cauley, P. Wilson0000-0001-9207-0564
Knutson, Heather A.0000-0002-5375-4725
France, Kevin0000-0002-1002-3674
Kreidberg, Laura0000-0003-0514-1147
Oklopčić, Antonija0000-0002-9584-6476
Redfield, Seth0000-0003-3786-3486
Shkolnik, Evgenya L.0000-0002-7260-5821
Additional Information:The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. A.O. gratefully acknowledges support from the Dutch Research Council NWO Veni grant.
Group:Division of Geological and Planetary Sciences
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20221122-564647900.5
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117991
Deposited By: Research Services Depository
Deposited On:06 Dec 2022 00:48
Last Modified:06 Dec 2022 17:25

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