TY - JOUR
T1 - The Hubble Space Telescope PanCET Program
T2 - Exospheric Mg ii and Fe ii in the Near-ultraviolet Transmission Spectrum of WASP-121b Using Jitter Decorrelation
AU - Sing, David K.
AU - Lavvas, Panayotis
AU - Ballester, Gilda E.
AU - Lecavelier Des Etangs, Alain
AU - Marley, Mark S.
AU - Nikolov, Nikolay
AU - Ben-Jaffel, Lotfi
AU - Bourrier, Vincent
AU - Buchhave, Lars A.
AU - Deming, Drake L.
AU - Ehrenreich, David
AU - Mikal-Evans, Thomas
AU - Kataria, Tiffany
AU - Lewis, Nikole K.
AU - López-Morales, Mercedes
AU - García Muñoz, Antonio
AU - Henry, Gregory W.
AU - Sanz-Forcada, Jorge
AU - Spake, Jessica J.
AU - Wakeford, Hannah R.
N1 - Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.
PY - 2019
Y1 - 2019
N2 - We 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.
AB - We 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.
KW - planets and satellites: atmospheres
KW - stars: individual (WASP-121)
KW - techniques: photometric
KW - techniques: spectroscopic
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U2 - 10.3847/1538-3881/ab2986
DO - 10.3847/1538-3881/ab2986
M3 - Article
AN - SCOPUS:85072325683
SN - 0004-6256
VL - 158
JO - Astronomical Journal
JF - Astronomical Journal
IS - 2
M1 - 91
ER -