Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published March 1, 2022 | Accepted Version + Published
Journal Article Open

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

Abstract

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.

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).

Attached Files

Published - Vissapragada_2022_ApJ_927_96.pdf

Accepted Version - 2201.09889.pdf

Files

2201.09889.pdf
Files (1.6 MB)
Name Size Download all
md5:601a88e84ea6989f536b6e15330ed161
767.6 kB Preview Download
md5:5b6d147159a43498efdfc381369e0f15
836.4 kB Preview Download

Additional details

Created:
August 22, 2023
Modified:
February 2, 2024