Redshifted Sodium Transient near Exoplanet Transit

Abstract Neutral sodium (Na i ) is an alkali metal with a favorable absorption cross section such that tenuous gases are easily illuminated at select transiting exoplanet systems. We examine both the time-averaged and time-series alkali spectral flux individually, over 4 nights at a hot Saturn system on a ∼2.8 day orbit about a Sun-like star WASP-49 A. Very Large Telescope/ESPRESSO observations are analyzed, providing new constraints. We recover the previously confirmed residual sodium flux uniquely when averaged, whereas night-to-night Na i varies by more than an order of magnitude. On HARPS/3.6 m Epoch II, we report a Doppler redshift at v Γ,NaD = + 9.7 ± 1.6 km s −1 with respect to the planet’s rest frame. Upon examining the lightcurves, we confirm night-to-night variability, on the order of ∼1%–4% in NaD, rarely coinciding with exoplanet transit, not readily explained by stellar activity, starspots, tellurics, or the interstellar medium. Coincident with the ∼+10 km s −1 Doppler redshift, we detect a transient sodium absorption event dF NaD / F ⋆ = 3.6% ± 1% at a relative difference of Δ F NaD ( t ) ∼ 4.4% ± 1%, lasting Δ t NaD ≳ 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly ∼−5.7 km s −1 , the radial velocity is rather at +15.4 km s −1 , far larger than any known exoplanet system. Given that the redshift magnitude v Γ is in between the Roche limit and dynamically stable satellite orbits, the transient sodium may be a putative indication of a natural satellite orbiting WASP-49 A b.

Authors

Publication Details

Journal
The Astrophysical Journal Letters
Published
2024-09-30
DOI
https://doi.org/10.3847/2041-8213/ad6b29
Citations
5
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
1.66

Funders

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article

Redshifted Sodium Transient near Exoplanet Transit

Santiago Torres, J. V. Seidel, Samuel Halverson, S. Charnoz et al.
5 citations
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Stellar, planetary, and galactic studies
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article

Redshifted Sodium Transient near Exoplanet Transit

Santiago Torres, J. V. Seidel, Samuel Halverson, S. Charnoz, H. J. Hoeijmakers, R. M. C. Lopes, Carl Schmidt, Angelica Psaridi, Andrea Gebek, Moritz Meyer zu Westram, A. Oza, Chloe Fisher, Renyu Hu, A. Wyttenbach, Katherine de Kleer, R. E. Johnson, Ashley Baker, Aurora Y. Kesseli, Aaron Bello-Arufe, N. M. Schneider, Athira Unni, S. G. Sousa, T. Sivarani, Ishita Bhatnagar
article en
5 citations

Abstract

Abstract Neutral sodium (Na i ) is an alkali metal with a favorable absorption cross section such that tenuous gases are easily illuminated at select transiting exoplanet systems. We examine both the time-averaged and time-series alkali spectral flux individually, over 4 nights at a hot Saturn system on a ∼2.8 day orbit about a Sun-like star WASP-49 A. Very Large Telescope/ESPRESSO observations are analyzed, providing new constraints. We recover the previously confirmed residual sodium flux uniquely when averaged, whereas night-to-night Na i varies by more than an order of magnitude. On HARPS/3.6 m Epoch II, we report a Doppler redshift at v Γ,NaD = + 9.7 ± 1.6 km s −1 with respect to the planet’s rest frame. Upon examining the lightcurves, we confirm night-to-night variability, on the order of ∼1%–4% in NaD, rarely coinciding with exoplanet transit, not readily explained by stellar activity, starspots, tellurics, or the interstellar medium. Coincident with the ∼+10 km s −1 Doppler redshift, we detect a transient sodium absorption event dF NaD / F ⋆ = 3.6% ± 1% at a relative difference of Δ F NaD ( t ) ∼ 4.4% ± 1%, lasting Δ t NaD ≳ 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly ∼−5.7 km s −1 , the radial velocity is rather at +15.4 km s −1 , far larger than any known exoplanet system. Given that the redshift magnitude v Γ is in between the Roche limit and dynamically stable satellite orbits, the transient sodium may be a putative indication of a natural satellite orbiting WASP-49 A b.

The Astrophysical Journal LettersVol. 973(2)
California Institute of Technology, Jet Propulsion Laboratory, Fundação para a Ciência e a Tecnologia
Openalex Percentile: Top 16%
Stellar, planetary, and galactic studies
1.66
DOIOpen Access PDFOpenAlex
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