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The Maximum Mass-loss Efficiency for a Photoionization-driven Isothermal Parker Wind

Vissapragada, Shreyas and Knutson, Heather A. and dos Santos, Leonardo A. and Wang, Lile and Dai, Fei (2022) The Maximum Mass-loss Efficiency for a Photoionization-driven Isothermal Parker Wind. Astrophysical Journal, 927 (1). Art. No. 96. ISSN 0004-637X. doi:10.3847/1538-4357/ac4e8a.

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Observations of present-day mass-loss rates for close-in transiting exoplanets provide a crucial check on models of planetary evolution. One common approach is to model the planetary absorption signal during the transit in lines like He I 10830 with an isothermal Parker wind, but this leads to a degeneracy between the assumed outflow temperature T₀ and the mass-loss rate Ṁ that can span orders of magnitude in Ṁ. In this study, we re-examine the isothermal Parker wind model using an energy-limited framework. We show that in cases where photoionization is the only heat source, there is a physical upper limit to the efficiency parameter ε corresponding to the maximal amount of heating. This allows us to rule out a subset of winds with high temperatures and large mass-loss rates as they do not generate enough heat to remain self-consistent. To demonstrate the utility of this framework, we consider spectrally unresolved metastable helium observations of HAT-P-11b, WASP-69b, and HAT-P-18b. For the former two planets, we find that only relatively weak (Ṁ ≲ 10^(11.5 g s⁻¹) outflows can match the metastable helium observations while remaining energetically self-consistent, while for HAT-P-18b all of the Parker wind models matching the helium data are self-consistent. Our results are in good agreement with more detailed self-consistent simulations and constraints from high-resolution transit spectra.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Vissapragada, Shreyas0000-0003-2527-1475
Knutson, Heather A.0000-0002-0822-3095
dos Santos, Leonardo A.0000-0002-2248-3838
Wang, Lile0000-0002-6540-7042
Dai, Fei0000-0002-8958-0683
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 October 22; revised 2022 January 7; accepted 2022 January 23; published 2022 March 8. We thank the anonymous referee for improving the quality of this paper and Antonija Oklopčić Yayaati Chachan, Konstantin Batygin, and Howard Isaacson for helpful conversations. S.V. is supported by an NSF Graduate Research Fellowship. H.A.K. acknowledges support from NSF CAREER grant 1555095. L.A.d.S. acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 724427, project Four Aces) and from the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation (SNSF). Facilities: ADS - , NASA Exoplanet Archive. - Software: numpy (Harris et al. 2020), scipy (Virtanen et al. 2020), astropy (Astropy Collaboration et al. 2013, 2018), matplotlib (Hunter 2007), p-winds (dos Santos et al. 2021).
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
European Research Council (ERC)724427
Swiss National Science Foundation (SNSF)UNSPECIFIED
Subject Keywords:Exoplanet atmospheres; Planetary atmospheres; Exoplanet astronomy; Exoplanet evolution
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Planetary atmospheres (1244); Exoplanet astronomy (486); Exoplanet evolution (491)
Record Number:CaltechAUTHORS:20220228-183329554
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Official Citation:Shreyas Vissapragada et al 2022 ApJ 927 96
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113656
Deposited By: George Porter
Deposited On:28 Feb 2022 21:46
Last Modified:17 Mar 2022 18:18

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