@article{f085498429e74680b062641c858253d6,
title = "Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b",
abstract = "The helium absorption triplet at a wavelength of 10833 a has been proposed as a way to probe the escaping atmospheres of exoplanets. Recently this feature was detected for the first time using Hubble Space Telescope (HST) WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3 observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at the 4σ confidence level. We compare our observations to a grid of 1D models of hydrodynamic escape to constrain the thermospheric temperatures and mass loss rate. We find that our data are best fit by models with high mass loss rates of g s-1. Although we do not detect the planetary wind directly, our data are consistent with the prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape. Nevertheless, the mass loss rate is low enough that the planet has only lost up to a few percent of its mass over its history, leaving its bulk composition largely unaffected. This matches the expectation from population statistics, which indicate that close-in planets with radii greater than 2 R ⊕ form and retain H/He-dominated atmospheres. We also confirm the independent detection of helium in HAT-P-11b obtained with the CARMENES instrument, making this the first exoplanet with the detection of the same signature of photoevaporation from both ground- and space-based facilities.",
keywords = "planets and satellites: atmospheres, planets and satellites: individual (HAT-P-11b)",
author = "Megan Mansfield and Bean, {Jacob L.} and Antonija Oklop{\v c}i{\'c} and Laura Kreidberg and D{\'e}sert, {Jean Michel} and Kempton, {Eliza M.R.} and Line, {Michael R.} and Fortney, {Jonathan J.} and Henry, {Gregory W.} and Matthias Mallonn and Stevenson, {Kevin B.} and Diana Dragomir and Romain Allart and Vincent Bourrier",
note = "Funding Information: We thank David Ehrenreich and Christophe Lovis for discussion of the CARMENES data. Support for program GO-14793 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. J.L.B. acknowledges support from the David and Lucile Packard Foundation. D.D. acknowledges support provided by NASA through Hubble Fellowship grant HSTHF2-51372.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. The work of R.A. and V.B. has been carried out in the framework of the National Centre for Competence in Research “PlanetS” supported by the Swiss National Science Foundation (SNSF). R.A. and V.B. acknowledge the financial support of the SNSF. This project has received funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (project FOUR ACES; grant agreement No. 724427). Based partly on data obtained with the STELLA robotic telescopes in Tenerife, an AIP facility jointly operated by AIP and IAC. Publisher Copyright: {\textcopyright} 2018. The American Astronomical Society. All rights reserved.",
year = "2018",
month = dec,
day = "1",
doi = "10.3847/2041-8213/aaf166",
language = "English (US)",
volume = "868",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "2",
}