Doppler shifted transient sodium detection by KECK/HIRES
Creators
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1.
University of California, Santa Cruz
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2.
Indian Institute of Astrophysics
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3.
California Institute of Technology
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4.
Jet Propulsion Lab
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5.
Lund University
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6.
European Southern Observatory
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7.
Boston University
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8.
NASA Exoplanet Science Institute
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9.
Ghent University
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10.
University of Bern
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11.
University of Oxford
Abstract
We carried out the first high-resolution transit observations of the exoplanet WASP-49 Ab with Keck/HIRES. Upon custom wavelength calibration we achieve a Doppler RV precision of < 60 m s⁻¹. This is an improvement in RV stability of roughly 240 m s⁻¹ with respect to the instrument standard. We report an average sodium flux residual of ΔF_(NaD)/F*(λ) ~3.2 ± 0.4 per cent (8.0σ) comparable to previous studies. Interestingly, an average Doppler shift of −6.2 ± 0.5 km s⁻¹ (12.4σ) is identified offset from the exoplanet rest frame. The velocity residuals in time trace a blueshift (vΓ,ingress ~ −10.3 ± 1.9 km s⁻¹) to redshift (vΓ,egress ~ + 4.1 ± 1.5 km s⁻¹) suggesting the origin of the observed sodium is unlikely from the atmosphere of the planet. The average Na light curves indicate a depth of ΔF_(NaD)/F*(t) ~0.47 ± 0.04 per cent (11.7σ) enduring ≤ 90 min with a half-max duration of ~40.1 min. Frequent high-resolution spectroscopic observations will be able to characterize the periodicity of the observed Doppler shifts. Considering the origin of the transient sodium gas is of unknown geometry, a co-orbiting natural satellite may be a likely source.
Copyright and License
Acknowledgement
We acknowledge the Keck telescope facility and archive facility for providing the observation time and reduced data. We would like to acknowledge the Exo-Io team for all the support and help. The research described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics Space Administration ©2025. All rights reserved. Some of the data presented herein were obtained at 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 William. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Data Availability
The observed Keck/HIRES data is available on the Keck Observatory Archive (KOA). The wavelength recalibrated data will be provided by the corresponding author upon reasonable request.
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2504.03974 (arXiv)
Funding
- W. M. Keck Foundation
Dates
- Accepted
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2025-04-02
- Available
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2025-04-07Published
- Available
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2025-04-23Corrected and typeset