Variable and Supersonic Winds in the Atmosphere of anUltrahot Giant Planet

Hot Jupiters receive intense irradiation from their stellar hosts. The resulting extreme environments in their atmospheres allow us to study the conditions that drive planetary atmospheric dynamics, e.g., globalscale winds. General circulation models predict daytonightside winds and equatorial jets with speeds of the order of a few km s1. To test these models, we apply highresolution transmission spectroscopy using the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) spectrograph on the Large Binocular Telescope to study the atmosphere of KELT9 b, an ultrahot Jupiter and currently the hottest known planet. We measure ~10 km s1 daytonightside winds traced by Fe II features in the planet’s atmosphere. This is at odds with previous literature (including data taken with PEPSI), which report no significant daytonightside winds on KELT9 b. We identify the cause of this discrepancy as due to an inaccurate ephemeris for KELT9 b in previous literature.

2D maps of transmission spectra, focusing on the six Fe II absorption lines in the PEPSI 2018 data set chosen for fitting Kp and v_wind. The blue track is the planet’s atmospheric absorption while the red track is the Doppler shadow from the RME; both tracks only form during a transit. Top panel displays fully in-transit observations. Middle panel shows the best-fit model from MCMC sampling. The bottom panel presents the residuals (data-model).

Read more: Pai Asnodkar et al. 2022, AJ, 163, 155