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arXiv · 2201.04154

Variable and super-sonic winds in the atmosphere of an ultra-hot giant planet

Anusha Pai Asnodkar·Ji Wang·Jason D. Eastman·P. Wilson Cauley·B. Scott Gaudi·Ilya Ilyin·Klaus Strassmeier
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Abstract

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., global-scale winds. General circulation models predict day-to-nightside winds and equatorial jets with speeds on the order of a few km $\mathrm{s^{-1}}$. To test these models, we apply high-resolution transmission spectroscopy using the PEPSI spectrograph on the Large Binocular Telescope to study the atmosphere of KELT-9 b, an ultra-hot Jupiter and currently the hottest known planet. We measure $\sim$10 km $\mathrm{s^{-1}}$ day-to-nightside 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 day-to-nightside winds on KELT-9 b. We identify the cause of this discrepancy as due to an inaccurate ephemeris for KELT-9 b in previous literature. We update the ephemeris, which shifts the mid-transit time by up to 10 minutes for previous datasets, resulting in consistent detections of blueshifts in all the datasets analyzed here. Furthermore, a comparison with archival HARPS-N datasets suggests temporal wind variability $\sim$5-8 km $\mathrm{s^{-1}}$ over timescales between weeks to years. Temporal variability of atmospheric dynamics on hot Jupiters is a phenomenon anticipated by certain general circulation models that has not been observed over these timescales until now. However, such large variability as we measure on KELT-9 b challenges general circulation models, which predict much lower amplitudes of wind variability over timescales between days to weeks.

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Anusha Pai Asnodkar, Ji Wang, Jason D. Eastman, P. Wilson Cauley, B. Scott Gaudi, Ilya Ilyin, Klaus Strassmeier. 2022-01-25. Variable and super-sonic winds in the atmosphere of an ultra-hot giant planet. https://doi.org/10.3847/1538-3881%2Fac51d2

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