---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
_id: '18306'
abstract:
- lang: eng
  text: 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 vΓ,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 dFNaD/F⋆
    = 3.6% ± 1% at a relative difference of ΔFNaD(t) ∼ 4.4% ± 1%, lasting ΔtNaD ≳
    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 vΓ 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.
acknowledgement: The research described in this Letter was carried out in part at
  the Jet Propulsion Laboratory, California Institute of Technology, under a contract
  with the National Aeronautics Space Administration, © 2024. California Institute
  of Technology. Government sponsorship acknowledged. A.V.O. and J.V.S. thank M. Lendl
  for constraints and discussions on the mass of WASP-49 A b. S.G.S acknowledges the
  support from FCT through Investigador FCT contract nr. CEECIND/00826/2018 and POPH/FSE
  (EC).
article_number: L53
article_processing_charge: Yes
article_type: original
arxiv: 1
author:
- first_name: Apurva V.
  full_name: Oza, Apurva V.
  last_name: Oza
- first_name: Julia V.
  full_name: Seidel, Julia V.
  last_name: Seidel
- first_name: H. Jens
  full_name: Hoeijmakers, H. Jens
  last_name: Hoeijmakers
- first_name: Athira
  full_name: Unni, Athira
  last_name: Unni
- first_name: Aurora Y.
  full_name: Kesseli, Aurora Y.
  last_name: Kesseli
- first_name: Carl A.
  full_name: Schmidt, Carl A.
  last_name: Schmidt
- first_name: Thirupathi
  full_name: Sivarani, Thirupathi
  last_name: Sivarani
- first_name: Aaron
  full_name: Bello-Arufe, Aaron
  last_name: Bello-Arufe
- first_name: Andrea
  full_name: Gebek, Andrea
  last_name: Gebek
- first_name: Moritz
  full_name: Meyer Zu Westram, Moritz
  last_name: Meyer Zu Westram
- first_name: Sérgio G.
  full_name: Sousa, Sérgio G.
  last_name: Sousa
- first_name: Rosaly M.C.
  full_name: Lopes, Rosaly M.C.
  last_name: Lopes
- first_name: Renyu
  full_name: Hu, Renyu
  last_name: Hu
- first_name: Katherine
  full_name: De Kleer, Katherine
  last_name: De Kleer
- first_name: Chloe
  full_name: Fisher, Chloe
  last_name: Fisher
- first_name: Sébastien
  full_name: Charnoz, Sébastien
  last_name: Charnoz
- first_name: Ashley D.
  full_name: Baker, Ashley D.
  last_name: Baker
- first_name: Samuel P.
  full_name: Halverson, Samuel P.
  last_name: Halverson
- first_name: Nick M.
  full_name: Schneider, Nick M.
  last_name: Schneider
- first_name: Angelica
  full_name: Psaridi, Angelica
  last_name: Psaridi
- first_name: Aurélien
  full_name: Wyttenbach, Aurélien
  last_name: Wyttenbach
- first_name: Santiago
  full_name: Torres Rodriguez, Santiago
  id: a8df4360-4328-11ee-8f1a-e502d0c83fc2
  last_name: Torres Rodriguez
  orcid: 0000-0002-3150-8988
- first_name: Ishita
  full_name: Bhatnagar, Ishita
  last_name: Bhatnagar
- first_name: Robert E.
  full_name: Johnson, Robert E.
  last_name: Johnson
citation:
  ama: Oza AV, Seidel JV, Hoeijmakers HJ, et al. Redshifted sodium transient near
    exoplanet transit. <i>Astrophysical Journal Letters</i>. 2024;973(2). doi:<a href="https://doi.org/10.3847/2041-8213/ad6b29">10.3847/2041-8213/ad6b29</a>
  apa: Oza, A. V., Seidel, J. V., Hoeijmakers, H. J., Unni, A., Kesseli, A. Y., Schmidt,
    C. A., … Johnson, R. E. (2024). Redshifted sodium transient near exoplanet transit.
    <i>Astrophysical Journal Letters</i>. IOP Publishing. <a href="https://doi.org/10.3847/2041-8213/ad6b29">https://doi.org/10.3847/2041-8213/ad6b29</a>
  chicago: Oza, Apurva V., Julia V. Seidel, H. Jens Hoeijmakers, Athira Unni, Aurora
    Y. Kesseli, Carl A. Schmidt, Thirupathi Sivarani, et al. “Redshifted Sodium Transient
    near Exoplanet Transit.” <i>Astrophysical Journal Letters</i>. IOP Publishing,
    2024. <a href="https://doi.org/10.3847/2041-8213/ad6b29">https://doi.org/10.3847/2041-8213/ad6b29</a>.
  ieee: A. V. Oza <i>et al.</i>, “Redshifted sodium transient near exoplanet transit,”
    <i>Astrophysical Journal Letters</i>, vol. 973, no. 2. IOP Publishing, 2024.
  ista: Oza AV, Seidel JV, Hoeijmakers HJ, Unni A, Kesseli AY, Schmidt CA, Sivarani
    T, Bello-Arufe A, Gebek A, Meyer Zu Westram M, Sousa SG, Lopes RMC, Hu R, De Kleer
    K, Fisher C, Charnoz S, Baker AD, Halverson SP, Schneider NM, Psaridi A, Wyttenbach
    A, Torres Rodriguez S, Bhatnagar I, Johnson RE. 2024. Redshifted sodium transient
    near exoplanet transit. Astrophysical Journal Letters. 973(2), L53.
  mla: Oza, Apurva V., et al. “Redshifted Sodium Transient near Exoplanet Transit.”
    <i>Astrophysical Journal Letters</i>, vol. 973, no. 2, L53, IOP Publishing, 2024,
    doi:<a href="https://doi.org/10.3847/2041-8213/ad6b29">10.3847/2041-8213/ad6b29</a>.
  short: A.V. Oza, J.V. Seidel, H.J. Hoeijmakers, A. Unni, A.Y. Kesseli, C.A. Schmidt,
    T. Sivarani, A. Bello-Arufe, A. Gebek, M. Meyer Zu Westram, S.G. Sousa, R.M.C.
    Lopes, R. Hu, K. De Kleer, C. Fisher, S. Charnoz, A.D. Baker, S.P. Halverson,
    N.M. Schneider, A. Psaridi, A. Wyttenbach, S. Torres Rodriguez, I. Bhatnagar,
    R.E. Johnson, Astrophysical Journal Letters 973 (2024).
date_created: 2024-10-13T22:01:49Z
date_published: 2024-10-01T00:00:00Z
date_updated: 2025-09-08T14:18:18Z
day: '01'
ddc:
- '520'
department:
- _id: LiBu
doi: 10.3847/2041-8213/ad6b29
external_id:
  arxiv:
  - '2409.19844'
  isi:
  - '001322169500001'
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intvolume: '       973'
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language:
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month: '10'
oa: 1
oa_version: Published Version
publication: Astrophysical Journal Letters
publication_identifier:
  eissn:
  - 2041-8213
  issn:
  - 2041-8205
publication_status: published
publisher: IOP Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: Redshifted sodium transient near exoplanet transit
tmp:
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  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
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