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Transmission Spectroscopy for the Warm Sub-Neptune HD 3167c: Evidence for Molecular Absorption and a Possible High-metallicity Atmosphere

Mikal-Evans, Thomas and Crossfield, Ian J. M. and Benneke, Björn and Kreidberg, Laura and Moses, Julie and Morley, Caroline V. and Thorngren, Daniel and Mollière, Paul and Hardegree-Ullman, Kevin K. and Brewer, John and Christiansen, Jessie L. and Ciardi, David R. and Dragomir, Diana and Dressing, Courtney and Fortney, Jonathan J. and Gorjian, Varoujan and Greene, Thomas P. and Hirsch, Lea A. and Howard, Andrew W. and Howell, Steve B. and Isaacson, Howard and Kosiarek, Molly R. and Krick, Jessica and Livingston, John H. and Lothringer, Joshua D. and Morales, Farisa Y. and Petigura, Erik A. and Schlieder, Joshua E. and Werner, Michael (2021) Transmission Spectroscopy for the Warm Sub-Neptune HD 3167c: Evidence for Molecular Absorption and a Possible High-metallicity Atmosphere. Astronomical Journal, 161 (1). Art. No. 18. ISSN 1538-3881. doi:10.3847/1538-3881/abc874.

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We present a transmission spectrum for the warm (500−600 K) sub-Neptune HD 3167c obtained using the Hubble Space Telescope Wide Field Camera 3 infrared spectrograph. We combine these data, which span the 1.125–1.643 μm wavelength range, with broadband transit measurements made using Kepler/K2 (0.6–0.9 μm) and Spitzer/IRAC (4–5 μm). We find evidence for absorption by at least one of H₂O, HCN, CO₂, and CH₄ (Bayes factor 7.4; 2.5σ significance), although the data precision does not allow us to unambiguously discriminate between these molecules. The transmission spectrum rules out cloud-free hydrogen-dominated atmospheres with metallicities ≤100× solar at >5.8σ confidence. In contrast, good agreement with the data is obtained for cloud-free models assuming metallicities >700× solar. However, for retrieval analyses that include the effect of clouds, a much broader range of metallicities (including subsolar) is consistent with the data, due to the degeneracy with cloud-top pressure. Self-consistent chemistry models that account for photochemistry and vertical mixing are presented for the atmosphere of HD 3167c. The predictions of these models are broadly consistent with our abundance constraints, although this is primarily due to the large uncertainties on the latter. Interior structure models suggest that the core mass fraction is >40%, independent of a rock or water core composition, and independent of atmospheric envelope metallicity up to 1000× solar. We also report abundance measurements for 15 elements in the host star, showing that it has a very nearly solar composition.

Item Type:Article
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URLURL TypeDescription Paper
Mikal-Evans, Thomas0000-0001-5442-1300
Crossfield, Ian J. M.0000-0002-1835-1891
Benneke, Björn0000-0001-5578-1498
Kreidberg, Laura0000-0003-0514-1147
Moses, Julie0000-0002-8837-0035
Morley, Caroline V.0000-0002-4404-0456
Thorngren, Daniel0000-0002-5113-8558
Mollière, Paul0000-0003-4096-7067
Hardegree-Ullman, Kevin K.0000-0003-3702-0382
Brewer, John0000-0002-9873-1471
Christiansen, Jessie L.0000-0002-8035-4778
Ciardi, David R.0000-0002-5741-3047
Dragomir, Diana0000-0003-2313-467X
Dressing, Courtney0000-0001-8189-0233
Fortney, Jonathan J.0000-0002-9843-4354
Gorjian, Varoujan0000-0002-8990-2101
Greene, Thomas P.0000-0002-8963-8056
Hirsch, Lea A.0000-0001-8058-7443
Howard, Andrew W.0000-0001-8638-0320
Howell, Steve B.0000-0002-2532-2853
Isaacson, Howard0000-0002-0531-1073
Kosiarek, Molly R.0000-0002-6115-4359
Krick, Jessica0000-0002-2413-5976
Livingston, John H.0000-0002-4881-3620
Lothringer, Joshua D.0000-0003-3667-8633
Morales, Farisa Y.0000-0001-9414-3851
Petigura, Erik A.0000-0003-0967-2893
Schlieder, Joshua E.0000-0001-5347-7062
Alternate Title:Transmission spectroscopy for the warm sub-Neptune HD3167c: evidence for molecular absorption and a possible high metallicity atmosphere
Additional Information:© 2020. The American Astronomical Society. Received 2020 July 31; revised 2020 October 19; accepted 2020 November 5; published 2020 December 7. The authors are grateful to the referee for constructive feedback that improved the quality of the manuscript. Support for HST program GO-15333 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. P.M. acknowledges support from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement No. 832428. D.D. acknowledges support from the TESS Guest Investigator Program grant 80NSSC19K1727 and NASA Exoplanet Research Program grant 18-2XRP18 2-0136. M.R.K. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. Facilities: HST(WFC3) - Hubble Space Telescope satellite, Spitzer(IRAC) - , Kepler(K2) - , Keck(HIRES). - Software: NumPy (van der Walt et al. 2011), SciPy (Virtanen et al. 2020), Matplotlib (Hunter 2007), emcee (Foreman-Mackey et al. 2013), batman (Kreidberg 2015), Astropy (Astropy Collaboration et al. 2013, 2018), pysynphot (STScI Development Team 2013), petitRadtrans (Mollière et al. 2019), PyMultinest (Buchner et al. 2014).
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAS 5-26555
European Research Council (ERC)832428
NASA18-2XRP18 2-0136
NSF Graduate Research FellowshipDGE-1339067
Subject Keywords:Exoplanet astronomy ; Exoplanets ; Exoplanet atmospheres
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet astronomy (486); Exoplanets (498); Exoplanet atmospheres (487)
Record Number:CaltechAUTHORS:20201208-105039183
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106968
Deposited By: George Porter
Deposited On:09 Dec 2020 15:29
Last Modified:16 Nov 2021 18:58

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