The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

Vidal‐Madjar, A.; Sing, David K.; Étangs, A. Lecavelier des; Ferlet, R.; Désert, Jean Michel; Hébrard, G.; Boisse, I.; Ehrenreich, D.; Moutou, C.

doi:10.1051/0004-6361/201015698

Cited by 72 publications

(68 citation statements)

References 43 publications

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“…In this N-body simulation, hydrogen atoms are released from GJ 436b's upper atmosphere as particles with a random initial velocity corresponding to a 10 000-K exobase. This temperature corresponds to the temperature expected in the upper atmospheres of hot jupiters (e.g., Lecavelier des Stone & Proga 2009) and was inferred from observations (Ballester et al 2007;Vidal-Madjar et al 2011). In any case, our results do not depend on this assumption because atoms are rapidly accelerated by the radiation pressure to velocities several times higher than their initial velocities.…”

Section: Observable Signature Of the Evaporating Atmospheresupporting

confidence: 83%

HST/STIS Lyman-αobservations of the quiet M dwarf GJ 436

Ehrenreich

Étangs

Delfosse

2011

A&A

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Lyman-α (Lyα) emission of neutral hydrogen (λ1215.67 Å) is the main contributor to the ultraviolet flux of low-mass stars such as M dwarfs. It is also the main light source used in studies of the evaporating upper atmospheres of transiting extrasolar planets with ultraviolet transmission spectroscopy. However, there are very few observations of the Lyα emissions of quiet M dwarfs, and none exist for those hosting exoplanets. Here, we present Lyα observations of the hot-Neptune host star GJ 436 with the Hubble Space Telescope Imaging Spectrograph (HST/STIS). We detect bright emission in the first resolved and high quality spectrum of a quiet M dwarf at Lyα. Using an energy diagram for exoplanets and an N-body particle simulation, this detection enables the possible exospheric signature of the hot Neptune to be estimated as a ∼11% absorption in the Lyα stellar emission, for a typical mass-loss rate of 10 10 g s −1 . The atmosphere of the planet GJ 436b is found to be stable to evaporation, and should be readily observable with HST. We also derive a correlation between X-ray and Lyα emissions for M dwarfs. This correlation will be useful for predicting the evaporation signatures of planets transiting other quiet M dwarfs.

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Section: Observable Signature Of the Evaporating Atmospheresupporting

confidence: 83%

HST/STIS Lyman-αobservations of the quiet M dwarf GJ 436

Ehrenreich

Étangs

Delfosse

2011

A&A

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“…of 10 −7 −10 −9 bar) above the result previously obtained at lower resolution . Our results suggest that a part of the sodium absorption occurs in the (lower) thermosphere, where heating by the stellar X/EUV photons occurs (Lammer et al 2003;Yelle 2004;Vidal-Madjar et al 2011;Koskinen et al 2013). Our interpretation relies on hydrostatic models, however, which might be questionable at very high altitudes.…”

Section: Na I D Doublet As a Probe Of The Upper Atmospherementioning

confidence: 52%

“…The Na  doublet was detected for the first time in HD 189733b with the High Resolution Spectrograph (HRS; R ∼ 60 000) mounted on the 9 m Hobby-Eberly Telescope and was confirmed in HD 209458b using the High Dispersion Spectrograph (HDS; R ∼ 45 000) on the 8 m Subaru telescope. Furthermore, the analysis of the spacebased detection of the sodium signature of these two planets by Sing et al (2008b), Vidal-Madjar et al (2011), and Huitson et al (2012), demonstrated the potential of resolving the transmitted stellar light by the planet atmosphere. Despite these encouraging works, the presence of scattering hazes and clouds (Lecavelier Des Etangs et al 2008a,b;Pont et al 2013) in several exoplanets prevented the detection of major chemical constituents at low to medium resolution even from space (e.g., Kreidberg et al 2014;Sing et al 2015).…”

Section: C-0488(e) Nomentioning

confidence: 99%

Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

Wyttenbach

Ehrenreich

Lovis

et al. 2015

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297

487

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Context. Atmospheric properties of exoplanets can be constrained with transit spectroscopy. At low spectral resolution, this technique is limited by the presence of clouds. The signature of atomic sodium (Na ), known to be present above the clouds, is a powerful probe of the upper atmosphere, where it can be best detected and characterized at high spectral resolution. Aims. Our goal is to obtain a high-resolution transit spectrum of HD 189733b in the region around the resonance doublet of Na  at 589 nm, to characterize the absorption signature that was previously detected from space at low resolution.Methods. We analyzed archival transit data of HD 189733b obtained with the HARPS spectrograph (R = 115 000) at the ESO 3.6-m telescope. We performed differential spectroscopy to retrieve the transit spectrum and light curve of the planet, implementing corrections for telluric contamination and planetary orbital motion. We compared our results to synthetic transit spectra calculated from isothermal models of the planetary atmosphere.Results. We spectrally resolve the Na  D doublet and measure line contrasts of 0.64 ± 0.07% (D2) and 0.40 ± 0.07% (D1) and FWHMs of 0.52 ± 0.08 Å. This corresponds to a detection at the 10σ level of excess of absorption of 0.32 ± 0.03% in a passband of 2 × 0.75 Å centered on each line. We derive temperatures of 2600 ± 600 K and 3270 ± 330 K at altitudes of 9800 ± 2800 and 12 700 ± 2600 km in the Na  D1 and D2 line cores, respectively. We measure a temperature gradient of ∼0.2 K km −1 in the region where the sodium absorption dominates the haze absorption from a comparison with theoretical models. We also detect a blueshift of 0.16 ± 0.04 Å (4σ) in the line positions. This blueshift may be the result of winds blowing at 8 ± 2 km s −1 in the upper layers of the atmosphere. Conclusions. We demonstrate the relevance of studying exoplanet atmospheres with high-resolution spectrographs mounted on 4-m-class telescopes. Our results pave the way for an in-depth characterization of physical conditions in the atmospheres of many exoplanetary systems with future spectrographs such as ESPRESSO on the VLT or HiReS and METIS on the E-ELT.

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“…The onset of the temperature rise at the Simulated atmospheres are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A75 1 Hot atmospheric layers of a planet where (extreme) ultraviolet radiation is absorbed. base of the thermosphere was confirmed in several observational studies of HD 209458 b and HD 189733 b (Ballester et al 2007;Sing et al 2008;Vidal-Madjar et al 2011b;Huitson et al 2012). Even at 1 au the thermosphere of Earth is heated to up to 2000 K (e.g., Banks & Kockarts 1973).…”

Section: Introductionmentioning

confidence: 56%

Simulating the escaping atmospheres of hot gas planets in the solar neighborhood

Salz

Czesla

Schneider

et al. 2016

A&A

175

326

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Absorption of high-energy radiation in planetary thermospheres is generally believed to lead to the formation of planetary winds. The resulting mass-loss rates can affect the evolution, particularly of small gas planets. We present 1D, spherically symmetric hydrodynamic simulations of the escaping atmospheres of 18 hot gas planets in the solar neighborhood. Our sample only includes strongly irradiated planets, whose expanded atmospheres may be detectable via transit spectroscopy using current instrumentation. The simulations were performed with the PLUTO-CLOUDY interface, which couples a detailed photoionization and plasma simulation code with a general MHD code. We study the thermospheric escape and derive improved estimates for the planetary mass-loss rates. Our simulations reproduce the temperature-pressure profile measured via sodium D absorption in HD 189733 b, but show still unexplained differences in the case of HD 209458 b. In contrast to general assumptions, we find that the gravitationally more tightly bound thermospheres of massive and compact planets, such as HAT-P-2 b are hydrodynamically stable. Compact planets dispose of the radiative energy input through hydrogen Lyα and free-free emission. Radiative cooling is also important in HD 189733 b, but it decreases toward smaller planets like GJ 436 b. Computing the planetary Lyα absorption and emission signals from the simulations, we find that the strong and cool winds of smaller planets mainly cause strong Lyα absorption but little emission. Compact and massive planets with hot, stable thermospheres cause small absorption signals but are strong Lyα emitters, possibly detectable with the current instrumentation. The absorption and emission signals provide a possible distinction between these two classes of thermospheres in hot gas planets. According to our results, WASP-80 and GJ 3470 are currently the most promising targets for observational follow-up aimed at detecting atmospheric Lyα absorption signals.

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The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

Cited by 72 publications

References 43 publications

HST/STIS Lyman-αobservations of the quiet M dwarf GJ 436

HST/STIS Lyman-αobservations of the quiet M dwarf GJ 436

Spectrally resolved detection of sodium in the atmosphere of HD 189733b with the HARPS spectrograph

Simulating the escaping atmospheres of hot gas planets in the solar neighborhood

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