Paper

Redshifted Sodium Transient near Exoplanet Transit

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

2024

Overview

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_ NaD =\\) +9.7 \\(\\) 1.6 km/s 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 Doppler redshift, we detect a transient sodium absorption event dF\\(_NaD\\)/F\\(_\\) = 3.6 \\(\\) 1 % at a relative difference of \\( F_NaD (t) \\) 4.4 \\(\\) 1 %, enduring \\( 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, the radial velocity is rather at +15.4 km/s, far larger than any known exoplanet system. Given that the redshift magnitude v\\(_\\) 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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Absorption cross sections / Alkali metals / Dynamic stability / Extrasolar planets / Interstellar matter / Natural satellites / Night / Radial velocity / Radiation pressure / Red shift / Roche limit / Satellite orbits / Sodium / Stellar activity / Transients (astronomy) / Transit / Very Large Telescope