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Escaping Helium from TOI 560.01, a Young Mini-Neptune

Zhang, Michael and Knutson, Heather A. and Wang, Lile and Dai, Fei and Barragán, Oscar (2022) Escaping Helium from TOI 560.01, a Young Mini-Neptune. Astronomical Journal, 163 (2). Art. No. 67. ISSN 0004-6256. doi:10.3847/1538-3881/ac3fa7.

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We report helium absorption from the escaping atmosphere of TOI 560.01 (HD 73583b), an R = 2.8 R_⊕, P = 6.4 day mini-Neptune orbiting a young (∼600 Myr) K dwarf. Using Keck/NIRSPEC, we detect a signal with an average depth of 0.68% ± 0.08% in the line core. The absorption signal repeats during a partial transit obtained a month later, but is marginally stronger and bluer, perhaps reflecting changes in the stellar wind environment. Ingress occurs on time, and egress occurs within 12 minutes of the white light egress, although absorption rises more gradually than it declines. This suggests that the outflow is slightly asymmetric and confined to regions close to the planet. The absorption signal also exhibits a slight 4 km s⁻¹ redshift rather than the expected blueshift; this might be explained if the planet has a modest orbital eccentricity, although the radial velocity data disfavors such an explanation. We use XMM-Newton observations to reconstruct the high-energy stellar spectrum and model the planet’s outflow with 1D and 3D hydrodynamic simulations. We find that our models generally overpredict the measured magnitude of the absorption during transit, the size of the blueshift, or both. Increasing the metallicity to 100× solar suppresses the signal, but the dependence of the predicted signal strength on metallicity is non-monotonic. Decreasing the assumed stellar EUV flux by a factor of three likewise suppresses the signal substantially.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Zhang, Michael0000-0002-0659-1783
Knutson, Heather A.0000-0002-5375-4725
Wang, Lile0000-0002-6540-7042
Dai, Fei0000-0002-8958-0683
Barragán, Oscar0000-0003-0563-0493
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 September 17; revised 2021 November 12; accepted 2021 November 29; published 2022 January 17. The helium 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. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Software: numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), dynesty (Speagle 2020), SAS.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
NASAXMM AO-20 #088287
Subject Keywords:Exoplanet atmospheres; Exoplanet astronomy; Exoplanets; Exoplanet evolution; Mini-Neptunes
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet astronomy (486); Exoplanets (498); Exoplanet evolution (491); Mini-Neptunes (1063)
Record Number:CaltechAUTHORS:20220113-182237138
Persistent URL:
Official Citation:Michael Zhang et al 2022 AJ 163 67
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112876
Deposited By: George Porter
Deposited On:13 Jan 2022 21:08
Last Modified:20 Jan 2022 16:48

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