Aeronomy, the study of Earth's upper atmosphere and its interaction with the local space environment, has long traced changes in the thermospheres of Earth and other solar system planets to solar variability in the X-ray and extreme-ultraviolet (collectively, XUV) bands. Extending comparative aeronomy to the short-period extrasolar planets may illuminate whether stellar XUV irradiation powers atmospheric outflows that change planetary radii on astronomical timescales. In recent years, near-IR transit spectroscopy of metastable Hei has been a prolific tracer of high-altitude planetary gas. We present a case study of exoplanet aeronomy using metastable Hei transit observations from Palomar Observatory's Wide Field InfraRed Camera and follow-up high-energy data from the Neil Gehrels Swift Observatory that were taken within 1 month of the WASP-69 system, a K-type main-sequence star with a well-studied hot Jupiter companion. Supplemented by archival data, we find that WASP-69's X-ray flux in 2023 was less than 50% of what was recorded in 2016 and that the metastable Hei absorption from WASP-69 b was lower in 2023 versus past epochs from 2017 to 2019. Via atmospheric modeling, we show that this time-variable metastable Hei signal is in the expected direction given the observed change in stellar XUV, possibly stemming from WASP-69's magnetic activity cycle. Our results underscore the ability of multiepoch, multiwavelength observations to paint a cohesive picture of the interaction between an exoplanet's atmosphere and its host star.
Exoplanet Aeronomy: A Case Study of WASP-69 b's Variable Thermosphere
Abstract
Copyright and License
© 2024. 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.
Acknowledgement
We appreciate the detailed peer-reviewing efforts from Gloria Guilluy and a second anonymous referee—their insightful reports helped us to improve the scientific content of this manuscript. We thank the Palomar Observatory telescope operators, support astronomers, hospitality and administrative staff, and directorate for their support. We are especially grateful to Tom Barlow, Carolyn Heffner, Diana Roderick, Kathleen Koviak, Isaac Wilson, Jennifer Milburn, and Andy Boden.
We are grateful to the Swift team for an expedient approval of our ToO request and for executing the observations. We acknowledge the use of public data from the Swift data archive. Parts of the results shown are based on archival observations obtained by XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This work has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) under the Exoplanet Exploration Program.
We appreciate that Romain Allart, Lisa Nortmann, Dakotah Tyler, and Gloria Guilluy shared their reduced spectra for WASP-69 b from SPIRou, CARMENES, and Keck, respectively—having these data allowed us to compare WIRC light curves to spectrally resolved results.
We benefited from useful conversations with Greg Laughlin, Sarbani Basu, Emma Louden, Christopher Lindsay, Earl Bellinger, Sam Cabot, Darryl Seligman, Quang Tran, Leonardo dos Santos, Fei Dai, Raissa Estrela, Jessie Christiansen, Elena Gallo, Parke Lloyd, Ethan Schreyer, Morgan Saidel, Kim Paragas, and Jonathan Gomez-Barrientos. Parts of this manuscript were checked for typographical errors and edited for clarity with assistance from OpenAI's GPT-4.
W.G.L. gratefully acknowledges support from the Department of Defense's National Defense Science & Engineering Graduate (NDSEG) Fellowship and Yale University's John F. Enders Fellowship for dissertation research travel. W.G.L. also thanks the LSST-DA Data Science Fellowship Program, which is funded by LSST-DA, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. A.D.F. acknowledges funding from NASA through the NASA Hubble Fellowship grant No. HST-HF2-51530.001-A awarded by STScI.
Software References
numpy (Harris et al. 2020), pandas (McKinney et al. 2011), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), astropy (Astropy Collaboration et al. 2013, 2018, 2022), photutils (Bradley et al. 2023), pymc3 (Salvatier et al. 2016), theano (Theano Development Team 2016), arviz (Kumar et al. 2019), exoplanet (Foreman-Mackey et al. 2021a, 2021b), ldtk (Husser et al. 2013; Parviainen & Aigrain 2015), starry (Luger et al. 2019), celerite2 (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), pymc3 (Salvatier et al. 2016), corner (Foreman-Mackey 2016), p-winds (dos Santos et al. 2022), HEASoft (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc), 2014), Xspec (Arnaud 1996)
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Additional details
- ISSN
- 1538-3881
- United States Department of Defense
- National Defense Science and Engineering Graduate (NDSEG) Fellowship
- Yale University
- Large Synoptic Survey Telescope Corporation
- Brinson Foundation
- Gordon and Betty Moore Foundation
- National Aeronautics and Space Administration
- NASA Hubble Fellowship HST-HF2-51530.001-A
- Caltech groups
- Division of Geological and Planetary Sciences, Thirty Meter Telescope