The Atmosphere of HAT-P-11 b

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The Atmosphere of HAT-P-11 b

Post by Sirius_Alpha on 24th September 2014, 2:26 pm

http://www.spacetelescope.org/news/heic1420/

Astronomers using data from the NASA/ESA Hubble Space Telescope, the Spitzer Space Telescope, and the Kepler Space Telescope have discovered clear skies and steamy water vapour on a planet outside our Solar System. The planet, known as HAT-P-11b, is about the size of Neptune, making it the smallest exoplanet ever on which water vapour has been detected. The results will appear in the online version of the journal Nature on 24 September 2014.

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Re: The Atmosphere of HAT-P-11 b

Post by Sirius_Alpha on 30th September 2014, 9:10 pm

Now on arXiv.

Water Vapour Absorption in the Clear Atmosphere of an exo-Neptune
http://arxiv.org/abs/1409.8349

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Re: The Atmosphere of HAT-P-11 b

Post by Sirius_Alpha on 1st November 2016, 8:21 pm

Discovery of the secondary eclipse of HAT-P-11 b
https://arxiv.org/abs/1611.00153

We report the detection of the secondary eclipse of HAT-P-11 b, a Neptune-sized planet orbiting an active K4 dwarf. Using all available short-cadence data of the Kepler mission, we derive refined planetary ephemeris increasing their precision by more than an order of magnitude. Our simultaneous primary and secondary transit modeling results in improved transit and orbital parameters. In particular, the precise timing of the secondary eclipse allows to pin down the orbital eccentricity to 0.26459+0.00069−0.00048. The secondary eclipse depth of 6.09+1.12−1.11 ppm corresponds to a 5.5σ detection and results in a geometric albedo of 0.390.07 for HAT-P-11 b, close to Neptune's value, which may indicate further resemblances between these two bodies. Due to the substantial orbital eccentricity, the planetary equilibrium temperature is expected to change significantly with orbital position and ought to vary between 630∘ K and 950∘ K, depending on the details of heat redistribution in the atmosphere of HAT-P-11 b.

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Re: The Atmosphere of HAT-P-11 b

Post by Sirius_Alpha on 6th December 2018, 9:39 pm

Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b
https://arxiv.org/abs/1812.02214

The helium absorption triplet at a wavelength of 10,833 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 M˙≈10^9 - 10^11 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.

Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet
https://arxiv.org/abs/1812.02189

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.

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