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.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/624389 |
| Date | 12 January 2017 |
| Creators | Loyd, R. O. Parke, Koskinen, T. T., France, Kevin, Schneider, Christian, Redfield, Seth |
| Contributors | Univ Arizona, Lunar & Planetary Lab |
| Publisher | IOP PUBLISHING LTD |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | © 2017. The American Astronomical Society. All rights reserved. |
| Relation | http://stacks.iop.org/2041-8205/834/i=2/a=L17?key=crossref.4749d6350936c02420fc7d0f62c34c9d |
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