Atmospheric Dynamics and the Variable Transit of KELT-9 b*

Abstract

We present a spectrally and temporally resolved detection of the optical Mg I triplet at 7.8σ in the extended atmosphere of the ultra-hot Jupiter KELT-9 b, adding to the list of detected metal species in the hottest gas giant currently known. Constraints are placed on the density and radial extent of the excited hydrogen envelope using simultaneous observations of Hα and Hβ under the assumption of a spherically symmetric atmosphere. We find that planetary rotational broadening of v rot = 8.2 +0.6 −0.7 km s −1 is necessary to reproduce the Balmer line transmission profile shapes, where the model including rotation is strongly preferred over the non-rotating model using a Bayesian information criterion comparison. The time-series of both metal line and hydrogen absorption show remarkable structure, suggesting that the atmosphere observed during this transit is dynamic rather than static. We detect a relative emission feature near the end of the transit which exhibits a P-Cygni-like shape, evidence of material moving at ≈ 50 − 100 km s −1 away from the planet. We hypothesize that the in-transit variability and subsequent P-Cygni-like profiles are due to a flaring event that caused the atmosphere to expand, resulting in unbound material being accelerated to high speeds by stellar radiation pressure. Further spectroscopic transit observations will help establish the frequency of such events.

Detection of Fe I and Fe II in the atmosphere of MASCARA-2b using a cross-correlation method

“…Moreover, Hoeijmakers et al (2018Hoeijmakers et al ( , 2019 reported the detection of Cr ii, Fe i, Fe ii, Mg ii, Na i, Sc ii, Ti ii and Y ii, as well as evidence of Ca i, Cr i, Co i and Sr ii in its atmosphere. Additionally Cauley et al (2019) detected in this planet H β and Mg i triplet. These atmospheric species have also been detected in the cooler UHJs WASP-18b (Arcangeli et al 2018), WASP-33b (von Essen et al 2018), WASP-12b (Jensen et al 2012), WASP-76b (Seidel et al 2019) and MASCARA-2b (Casasayas-Barris et al 2018.…”

“…Fe I and Fe II have been previously detected in the atmosphere of KELT-9b by Hoeijmakers et al (2018Hoeijmakers et al ( , 2019 using the cross-correlation method and by Cauley et al (2019) using transmission spectroscopy. KELT-9b, however, has an extremely high day-side equilibrium temperature (T eq = 3920 K), while MASCARA-2b's is much lower (T eq = 2260 K).…”

Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter KELT-9b

“…Also, Yan & Henning (2018) reported an extended hydrogen atmosphere (∼ 1.64 R p ) using Hα observations with the CARMENES spectrograph. The Hα detetion was confirmed by Cauley et al (2019), who observed variability in the in-transit absorption light curve suggesting that the transiting gas is not uniform. Using high-resolution optical spectra from HARPS-N during four separate KELT-9b transits Borsa et al (2019) observed the atmospheric Rossiter-McLaughlin effect.…”

Detection of Na, K, and Hαabsorption in the atmosphere of WASP-52b using ESPRESSO

“…For Hα, we have measured a line FWHM of 15.4 km s −1 , i.e., σ = FWHM/2.355 = 6.5 km s −1 . Assuming that Hα originates in a similar layer to the Na doublet and that its line width is set by thermal broadening and the maximum optical depth at line center, based on the equations (3) and (4) In addition to WASP-52b, five other planets have simultaneous detections of Na and Hα, including HD 189733b Jensen et al 2012;Cauley et al 2015Cauley et al , 2016Huang et al 2017), KELT-20b (Casasayas-Barris et al 2019), KELT-9b (Yan & Henning 2018;Cauley et al 2019), WASP-12b (Jensen et al 2018). and WASP-121b (Cabot et al 2020).…”