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Detection of Ongoing Mass Loss from HD 63433c, a Young Mini-Neptune

Zhang, Michael and Knutson, Heather A. and Wang, Lile and Dai, Fei and dos Santos, Leonardo A. and Fossati, Luca and Henry, Gregory W. and Ehrenreich, David and Alibert, Yann and Hoyer, Sergio and Wilson, Thomas G. and Bonfanti, Andrea (2022) Detection of Ongoing Mass Loss from HD 63433c, a Young Mini-Neptune. Astronomical Journal, 163 (2). Art. No. 68. ISSN 0004-6256. doi:10.3847/1538-3881/ac3f3b.

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We detect Lyα absorption from the escaping atmosphere of HD 63433c, a R = 2.67 R_⊕, P = 20.5 day mini-Neptune orbiting a young (440 Myr) solar analog in the Ursa Major Moving Group. Using Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph, we measure a transit depth of 11.1 ± 1.5% in the blue wing and 8 ± 3% in the red. This signal is unlikely to be due to stellar variability, but should be confirmed by an upcoming second transit observation with HST. We do not detect Lyα absorption from the inner planet, a smaller R = 2.15 R_⊕ mini-Neptune on a 7.1 day orbit. We use Keck/NIRSPEC to place an upper limit of 0.5% on helium absorption for both planets. We measure the host star's X-ray spectrum and mid-ultraviolet flux with XMM-Newton, and model the outflow from both planets using a 3D hydrodynamic code. This model provides a reasonable match to the light curve in the blue wing of the Lyα line and the helium nondetection for planet c, although it does not explain the tentative red wing absorption or reproduce the excess absorption spectrum in detail. Its predictions of strong Lyα and helium absorption from b are ruled out by the observations. This model predicts a much shorter mass-loss timescale for planet b, suggesting that b and c are fundamentally different: while the latter still retains its hydrogen/helium envelope, the former has likely lost its primordial atmosphere.

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
dos Santos, Leonardo A.0000-0002-2248-3838
Fossati, Luca0000-0003-4426-9530
Henry, Gregory W.0000-0003-4155-8513
Ehrenreich, David0000-0001-9704-5405
Alibert, Yann0000-0002-4644-8818
Hoyer, Sergio0000-0003-3477-2466
Wilson, Thomas G.0000-0001-8749-1962
Bonfanti, Andrea0000-0002-1916-5935
Additional Information:© 2022. 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 June 9; revised 2021 November 9; accepted 2021 November 30; published 2022 January 17. This study was based on observations with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for this work was provided by NASA through grant No. GO-16319 from STScI. This study also utilized data 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. L.D.S. and D.E. acknowledge that this project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (project Four Aces grant agreement No. 724427), and it has been carried out in the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). T.G.W. acknowledges support from STFC consolidated grant No. ST/R000824/1. S.H. acknowledges CNES funding through the grant 837319. S.H. acknowledges CNES funding through the grant 837319. G.W.H. acknowledges long-term support of the APT program from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence Program. Software: numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), stan(Stan Development Team 2018), stistools, SAS, HEAsoft.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
European Research Council (ERC)724427
Swiss National Science Foundation (SNSF)UNSPECIFIED
Science and Technology Facilities Council (STFC)ST/R000824/1
Centre National d'Études Spatiales (CNES)837319
Tennessee State UniversityUNSPECIFIED
State of Tennessee Centers of Excellence programUNSPECIFIED
Subject Keywords:Exoplanet atmospheres; Exoplanet atmospheric composition; Exoplanet systems; Exoplanets; Mini Neptunes; Exoplanet evolution; Extrasolar rocky planets; Exosphere
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet atmospheric composition (2021); Exoplanet systems (484); Exoplanets (498); Mini Neptunes (1063); Exoplanet evolution (491); Extrasolar rocky planets (511); Exosphere (499)
Record Number:CaltechAUTHORS:20220119-572901000
Persistent URL:
Official Citation:Michael Zhang et al 2022 AJ 163 68
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112995
Deposited By: George Porter
Deposited On:19 Jan 2022 22:45
Last Modified:19 Jan 2022 22:45

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