Redshifted Sodium Transient near Exoplanet Transit

Summary, in English

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.

• Author: Apurva V. Oza; Julia V. Seidel; H. Jens Hoeijmakers; Athira Unni; Aurora Y. Kesseli; Carl A. Schmidt; Thirupathi Sivarani; Aaron Bello-Arufe; Andrea Gebek; Moritz Meyer zu Westram; Sérgio G. Sousa; Rosaly M.C. Lopes; Renyu Hu; Katherine de Kleer; Chloe Fisher; Sébastien Charnoz; Ashley D. Baker; Samuel P. Halverson; Nick M. Schneider; Angelica Psaridi; Aurélien Wyttenbach; Santiago Torres; Ishita Bhatnagar; Robert E. Johnson
• Department/s: eSSENCE: The e-Science Collaboration; Astrophysics
• Publishing year: 2024-10-01
• Language: English
• Publication/Series: Astrophysical Journal Letters
• Volume: 973
• Issue: 2
• Links: http://dx.doi.org/10.3847/2041-8213/ad6b29
• Document type: Journal article
• Publisher: IOP Publishing
• Topic: Astronomy, Astrophysics and Cosmology
• Status: Published
• ISBN/ISSN/Other: ISSN: 2041-8205