Ultraviolet C ii and Si iii Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b
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Univ Arizona, Lunar & Planetary LabIssue Date
2017-01-12Keywords
planet-star interactionsplanets and satellites: atmospheres
planets and satellites: individual (GJ436b)
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IOP PUBLISHING LTDCitation
Ultraviolet C ii and Si iii Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b 2017, 834 (2):L17 The Astrophysical JournalRights
© 2017. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
Hydrogen gas evaporating from the atmosphere of the hot-Neptune GJ436b absorbs over 50% of the stellar Lya emission during transit. Given the planet's atmospheric composition and energy-limited escape rate, this hydrogen outflow is expected to entrain heavier atoms such as C and O. We searched for C and Si in the escaping atmosphere of GJ436b using far-ultraviolet Hubble Space Telescope COS G130M observations made during the planet's extended H I transit. These observations show no transit absorption in the C II 1334,1335 angstrom and Si III 1206 angstrom lines integrated over [-100, 100] km s(-1), imposing 95% (2 sigma) upper limits of 14% (C II) and 60% (Si III) depth on the transit of an opaque disk and 22% (C II) and 49% (Si III) depth on an extended highly asymmetric transit similar to that of H I Ly alpha. C+ is likely present in the outflow according to a simulation we carried out using a spherically symmetric photochemical-hydrodynamical model. This simulation predicts an similar to 2% transit over the integrated bandpass, consistent with the data. At line center, we predict the C II transit depth to be as high as 19%. Our model predicts a neutral hydrogen escape rate of 1.6 x 10(9) g s(-1) (3.1 x 10(9) g s(-1) for all species) for an upper atmosphere composed of hydrogen and helium.ISSN
2041-8213Version
Final published versionSponsors
HST Guest Observing program [13650]; NASA [HST-GO-13650.01]Additional Links
http://stacks.iop.org/2041-8205/834/i=2/a=L17?key=crossref.4749d6350936c02420fc7d0f62c34c9dae974a485f413a2113503eed53cd6c53
10.3847/2041-8213/834/2/L17