Redshifted Sodium Transient near Exoplanet Transit

October 2024 • 2024ApJ...973L..53O

Authors • Oza, Apurva V. • Seidel, Julia V. • Hoeijmakers, H. Jens • Unni, Athira • Kesseli, Aurora Y. • Schmidt, Carl A. • Sivarani, Thirupathi • Bello-Arufe, Aaron • Gebek, Andrea • Meyer zu Westram, Moritz • Sousa, Sérgio G. • Lopes, Rosaly M. C. • Hu, Renyu • de Kleer, Katherine • Fisher, Chloe • Charnoz, Sébastien • Baker, Ashley D. • Halverson, Samuel P. • Schneider, Nick M. • Psaridi, Angelica • Wyttenbach, Aurélien • Torres, Santiago • Bhatnagar, Ishita • Johnson, Robert E.

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 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2024ApJ...973L..53O
• PREPRINT http://arxiv.org/abs/2409.19844
• DATA http://archive.eso.org/bin/ads2eso?2024ApJ...973L..53O
• ELECTR https://doi.org/10.3847%2F2041-8213%2Fad6b29