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No Escaping Helium from 55 Cnc e

Zhang, Michael and Knutson, Heather A. and Wang, Lile and Dai, Fei and Oklopčić, Antonija and Hu, Renyu (2021) No Escaping Helium from 55 Cnc e. Astronomical Journal, 161 (4). Art. No. 181. ISSN 1538-3881. doi:10.3847/1538-3881/abe382.

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We search for escaping helium from the hot super-Earth 55 Cnc e by taking high-resolution spectra of the 1083 nm line during two transits using Keck/NIRSPEC. We detect no helium absorption down to a 90% upper limit of 250 ppm in excess absorption or 0.27 mÅ in equivalent width. This corresponds to a mass-loss rate of less than ~10⁹ g s⁻¹ assuming a Parker wind model with a plausible exosphere temperature of 5000–6000 K, although the precise constraint is heavily dependent on model assumptions. We consider both hydrogen- and helium-dominated atmospheric compositions and find similar bounds on the mass-loss rate in both scenarios. Our hydrodynamical models indicate that if a lightweight atmosphere exists on 55 Cnc e, our observations would have easily detected it. Together with the nondetection of Lyα absorption by Ehrenreich et al., our helium nondetection indicates that 55 Cnc e either never accreted a primordial atmosphere in the first place or lost its primordial atmosphere shortly after the dissipation of the gas disk.

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
Oklopčić, Antonija0000-0002-9584-6476
Hu, Renyu0000-0003-2215-8485
Additional Information:© 2021 The American Astronomical Society. Received 2020 September 9; revised 2021 February 1; accepted 2021 February 3; published 2021 March 12. 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. M.Z. would like to acknowledge Joe Ninan, who was indispensable in deciphering the mysteries of NIRSPEC systematics. He also acknowledges Jacob Bean for sending most of the data plotted in Figure 8. Software: numpy (van der Walt et al. 2011), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), dynesty (Speagle 2020), corner (Foreman-Mackey 2016).
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:Exoplanet atmospheres; Exoplanet atmospheric composition; High resolution spectroscopy; Super Earths
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet atmospheric composition (2021); High resolution spectroscopy (2096); Super Earths (1655)
Record Number:CaltechAUTHORS:20210111-160832533
Persistent URL:
Official Citation:Michael Zhang et al 2021 AJ 161 181
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107403
Deposited By: George Porter
Deposited On:12 Jan 2021 16:34
Last Modified:16 Nov 2021 19:02

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