Preprint article · Journal article
The Hubble Space Telescope PanCET Program: Exospheric Mg II and Fe II in the Near-ultraviolet Transmission Spectrum of WASP-121b Using Jitter Decorrelation
Johns Hopkins University1
Cornell University2
Harvard-Smithsonian Center for Astrophysics3
Technical University of Berlin4
Tennessee State University5
CSIC6
University of Exeter7
Space Telescope Science Institute8
CNRS9
University of Arizona10
National Aeronautics and Space Administration11
University of Geneva12
Astrophysics and Atmospheric Physics, National Space Institute, Technical University of Denmark13
National Space Institute, Technical University of Denmark14
University of Maryland, College Park15
Massachusetts Institute of Technology16
...and 6 moreWe present Hubble Space Telescope (HST) near-ultraviolet (NUV) transits of the hot Jupiter WASP-121b, acquired as part of the PanCET program. Time-series spectra during two transit events were used to measure the transmission spectra between 2280 and 3070 Å at a resolution of 30,000. Using HST data from 61 Space Telescope Imaging Spectrograph visits, we show that data from HST's Pointing Control System can be used to decorrelate the instrument systematic errors (jitter decorrelation), which we used to fit the WASP-121b light curves.
The NUV spectra show very strong absorption features, with the NUV white light curve found to be larger than the average optical and near-infrared value at 6σ confidence. We identify and spectrally resolve absorption from the Mg ii doublet in the planetary exosphere at a 5.9σ confidence level. The Mg ii doublet is observed to reach altitudes of R pl/R star = 0.284 ± 0.037 for the 2796 Å line and 0.242 ± 0.0431 for the 2804 Å line, which exceeds the Roche lobe size as viewed in transit geometry (R eqRL/R star = 0.158).
We also detect and resolve strong features of the Fe ii UV1 and UV2 multiplets, and observe the lines reaching altitudes of R pl/R star ≈ 0.3. At these high altitudes, the atmospheric Mg ii and Fe ii gas is not gravitationally bound to the planet, and these ionized species may be hydrodynamically escaping or could be magnetically confined.
Refractory Mg and Fe atoms at high altitudes also indicate that these species are not trapped into condensate clouds at depth, which places constraints on the deep interior temperature.
Language: | English |
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Year: | 2019 |
Pages: | 91 |
ISSN: | 15383881 and 00046256 |
Types: | Preprint article and Journal article |
DOI: | 10.3847/1538-3881/ab2986 |
ORCIDs: | Buchhave, Lars A. , 0000-0001-6050-7645 , 0000-0002-5360-3660 , 0000-0002-5251-2943 , 0000-0002-6500-3574 , 0000-0003-4047-2793 , 0000-0002-9148-034X , 0000-0001-9704-5405 , 0000-0001-5442-1300 , 0000-0003-3759-9080 , 0000-0002-8507-1304 , 0000-0003-3204-8183 , 0000-0003-1756-4825 , 0000-0003-4155-8513 , 0000-0002-1600-7835 and 0000-0003-4328-3867 |
Planets and satellites: atmospheres Stars: individual (WASP-121) Techniques: photometric Techniques: spectroscopic