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Redshifted Sodium Transient near Exoplanet Transit

Oza, Apurva V. ; Seidel, Julia V. ; Hoeijmakers, H. Jens LU orcid ; Unni, Athira ; Kesseli, Aurora Y. ; Schmidt, Carl A. ; Sivarani, Thirupathi ; Bello-Arufe, Aaron ; Gebek, Andrea and Meyer zu Westram, Moritz , et al. (2024) In Astrophysical Journal Letters 973(2).
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... (More)

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 ΔF NaD(t) ∼ 4.4% ± 1%, lasting Δt 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.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Astrophysical Journal Letters
volume
973
issue
2
article number
L53
publisher
IOP Publishing
external identifiers
  • scopus:85205549504
ISSN
2041-8205
DOI
10.3847/2041-8213/ad6b29
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2024. The Author(s).
id
98d9355a-04aa-4b8b-a506-c31618473f2b
date added to LUP
2024-12-18 11:19:42
date last changed
2025-05-22 00:06:10
@article{98d9355a-04aa-4b8b-a506-c31618473f2b,
  abstract     = {{<p>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 <sub>Γ,NaD</sub> = + 9.7 ± 1.6 km s<sup>−1</sup> 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<sup>−1</sup> Doppler redshift, we detect a transient sodium absorption event dF <sub>NaD</sub>/F <sub>⋆</sub> = 3.6% ± 1% at a relative difference of ΔF <sub>NaD</sub>(t) ∼ 4.4% ± 1%, lasting Δt <sub>NaD</sub> ≳ 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly ∼−5.7 km s<sup>−1</sup>, the radial velocity is rather at +15.4 km s<sup>−1</sup>, far larger than any known exoplanet system. Given that the redshift magnitude v <sub>Γ</sub> 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.</p>}},
  author       = {{Oza, Apurva V. and Seidel, Julia V. and Hoeijmakers, H. Jens and Unni, Athira and Kesseli, Aurora Y. and Schmidt, Carl A. and Sivarani, Thirupathi and Bello-Arufe, Aaron and Gebek, Andrea and Meyer zu Westram, Moritz and Sousa, Sérgio G. and Lopes, Rosaly M.C. and Hu, Renyu and de Kleer, Katherine and Fisher, Chloe and Charnoz, Sébastien and Baker, Ashley D. and Halverson, Samuel P. and Schneider, Nick M. and Psaridi, Angelica and Wyttenbach, Aurélien and Torres, Santiago and Bhatnagar, Ishita and Johnson, Robert E.}},
  issn         = {{2041-8205}},
  language     = {{eng}},
  month        = {{10}},
  number       = {{2}},
  publisher    = {{IOP Publishing}},
  series       = {{Astrophysical Journal Letters}},
  title        = {{Redshifted Sodium Transient near Exoplanet Transit}},
  url          = {{http://dx.doi.org/10.3847/2041-8213/ad6b29}},
  doi          = {{10.3847/2041-8213/ad6b29}},
  volume       = {{973}},
  year         = {{2024}},
}