Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet. (arXiv:1812.02189v1 [astro-ph.EP])

Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet. (arXiv:1812.02189v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Allart_R/0/1/0/all/0/1">R. Allart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourrier_V/0/1/0/all/0/1">V. Bourrier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovis_C/0/1/0/all/0/1">C. Lovis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ehrenreich_D/0/1/0/all/0/1">D. Ehrenreich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spake_J/0/1/0/all/0/1">J.J. Spake</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wyttenbach_A/0/1/0/all/0/1">A. Wyttenbach</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pino_L/0/1/0/all/0/1">L. Pino</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pepe_F/0/1/0/all/0/1">F. Pepe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sing_D/0/1/0/all/0/1">D.K. Sing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Etangs_A/0/1/0/all/0/1">A. Lecavelier des Etangs</a>

Stellar heating causes atmospheres of close-in exoplanets to expand and
escape. These extended atmospheres are difficult to observe because their main
spectral signature – neutral hydrogen at ultraviolet wavelengths – is strongly
absorbed by interstellar medium. We report the detection of the near-infrared
triplet of neutral helium in the transiting warm Neptune-mass exoplanet
HAT-P-11b using ground-based, high-resolution observations. The helium feature
is repeatable over two independent transits, with an average absorption depth
of 1.08+/-0.05%. Interpreting absorption spectra with 3D simulations of the
planet’s upper atmosphere suggests it extends beyond 5 planetary radii, with a
large scale height and a helium mass loss rate =< 3x10^5 g/s. A net blue-shift of the absorption might be explained by high-altitude winds flowing at 3 km/s from day to night-side.

Stellar heating causes atmospheres of close-in exoplanets to expand and
escape. These extended atmospheres are difficult to observe because their main
spectral signature – neutral hydrogen at ultraviolet wavelengths – is strongly
absorbed by interstellar medium. We report the detection of the near-infrared
triplet of neutral helium in the transiting warm Neptune-mass exoplanet
HAT-P-11b using ground-based, high-resolution observations. The helium feature
is repeatable over two independent transits, with an average absorption depth
of 1.08+/-0.05%. Interpreting absorption spectra with 3D simulations of the
planet’s upper atmosphere suggests it extends beyond 5 planetary radii, with a
large scale height and a helium mass loss rate =< 3×10^5 g/s. A net blue-shift
of the absorption might be explained by high-altitude winds flowing at 3 km/s
from day to night-side.

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