ENERGETIC NEUTRAL ATOMS AROUND HD 209458b: ESTIMATIONS OF MAGNETOSPHERIC PROPERTIES

Ekenbäck, A.; Holmström, Mats; Würz, Peter; Grießmeier, Jean-Mathias; Lämmer, H.; Selsis, F.; Penz, T.

doi:10.1088/0004-637x/709/2/670

Cited by 122 publications

(131 citation statements)

References 46 publications

Supporting

Mentioning

127

Contrasting

Order By: Relevance

“…2.4), and absorption arising mainly from hydrogen in the Roche lobe. Energetic neutral atoms have also been proposed as the source for the absorption signatures of HD 209458b (Holmström et al 2008;Ekenbäck et al 2010;Tremblin & Chiang 2013). Although interactions with stellar wind protons cannot be excluded, our results show that radiation pressure alone, with its strength directly constrained by the observations, is enough to explain the data, without the need for additional acceleration mechanisms and additional degrees of freedom in the model.…”

Section: Ionization Lifetimementioning

confidence: 64%

“…Schneiter et al (2007) developed a 3D model of the hydrodynamical interaction between the gas escaping from HD 209458b and the stellar wind, neglecting the photoionization A&A 557, A124 (2013) of the neutral hydrogen. Alternatively, in the 3D model developed by Holmström et al (2008) and Ekenbäck et al (2010) the production of energetic neutral atoms through the interaction of the planetary and stellar winds at high altitude from the planet is presented as the source for the observed hydrogen. In these 3D models the escaping gas is shaped into a cometary cloud.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

3D model of hydrogen atmospheric escape from HD 209458b and HD 189733b: radiative blow-out and stellar wind interactions

Bourrier

Étangs

2013

A&A

149

View full text Add to dashboard Cite

Transit observations in the Lyman-α line of the hot-Jupiters HD 209458b and HD 189733b revealed strong signatures of neutral hydrogen escaping the planets' upper atmospheres. Here we present a 3D particle model of the dynamics of the escaping atoms. This model is used to calculate theoretical Lyman-α absorption line profiles, which can be directly compared with the absorption observed in the blue wing of the line during the planets' transit. For HD 209458b, the observed velocities of the planet-escaping atoms up to −130 km s −1 are naturally explained by radiation-pressure acceleration. The observations are well-fitted with an ionizing flux of about 3−4 times the solar value and a hydrogen escape rate in the range 10 9 −10 11 g s −1 , in agreement with theoretical predictions. For HD 189733b, absorption by neutral hydrogen has been observed in September 2011 in the velocity range −230 to −140 km s −1 . These velocities are higher than for HD 209458b and require an additional acceleration mechanism for the escaping hydrogen atoms, which could be interactions with stellar wind protons. We constrain the stellar wind (temperature ∼3 × 10 4 K, velocity 200 ± 20 km s −1 and density in the range 10 3 −10 7 cm −3 ) as well as the escape rate (4 × 10 8 −10 11 g s −1 ) and ionizing flux (6−23 times the solar value). We also reveal the existence of an "escape-limited" saturation regime in which most of the gas escaping the planet interacts with the stellar protons. In this regime, which occurs at proton densities above ∼3 × 10 5 cm −3 , the amplitude of the absorption signature is limited by the escape rate and does not depend on the wind density. The non-detection of escaping hydrogen in earlier observations in April 2010 can be explained by the suppression of the stellar wind at that time, or an escape rate of about an order of magnitude lower than in 2011. For both planets, best-fit simulations show that the escaping atmosphere has the shape of a cometary tail. Simulations also revealed that the radiative blow-out of the gas causes spectro-temporal variability of the absorption profile as a function of time during and after the planetary transit. Because no such variations are observed when the absorbing hydrogen atoms are accelerated through interactions with the stellar wind, this may be used to distinguish between the two scenarios.

show abstract

Section: Ionization Lifetimementioning

confidence: 64%

Section: Introductionmentioning

confidence: 99%

3D model of hydrogen atmospheric escape from HD 209458b and HD 189733b: radiative blow-out and stellar wind interactions

Bourrier

Étangs

2013

A&A

149

View full text Add to dashboard Cite

show abstract

“…In the models developed by Holmström et al (2008) and Ekenbäck et al (2010), the observed hydrogen is produced through charge exchange between the stellar wind and the planetary escaping exosphere. Even in these last models, neutral hydrogen escaping the planet is required for charge exchange with hot protons of the stellar wind.…”

Section: Evaporation Of Hot Jupitersmentioning

confidence: 99%

Atmospheric escape from HD 189733b observed in H I Lyman-α: detailed analysis of HST/STIS September 2011 observations

Bourrier

Étangs

Dupuy

et al. 2013

A&A

141

115

View full text Add to dashboard Cite

Observations of transits of the hot giant exoplanet HD 189733b in the unresolved H i Lyman-α line show signs of hydrogen escaping the upper atmosphere of the planet. New resolved Lyman-α observations obtained with the STIS spectrograph onboard the Hubble Space Telescope in April 2010 and September 2011 confirmed that the planet is evaporating, and furthermore discovered significant temporal variations in the physical conditions of its evaporating atmosphere. Here we present a detailed analysis of the September 2011 observations of HD 189733b, when an atmospheric signature was detected. We present specific methods to find and characterize this absorption signature of escaping hydrogen in the Lyman-α line, and to calculate its false-positive probability, found to be 3.6%. Taking advantage of the spectral resolution and high sensitivity of the STIS spectrograph, we also present new results on temporal and spectro-temporal variability of this absorption feature. We also report the observation of HD 189733b in other lines (Si iii at 1206.5 Å, N v at 1240 Å). Variations in these lines could be explained either by early occultation by a bow-shock rich in highly ionized species, or by stellar variations.

show abstract

“…3, we show two modeled hydrogen corona and ENAs as well as the attenuation spectra in comparison with the HST/STIS in and out off transit observations of Vidal-Madjar et al (2003). We apply the same plasma flow, exosphere, ENA production and Lyman-α attenuation model described in detail in Holmström et al (2008) and Ekenbäck et al (2010) to the planetary parameters favored by Koskinen et al (2010). The results shown in Fig.…”

Section: Characterization Of the Upper Atmosphere-magnetosphere Envirmentioning

confidence: 99%

“…Because of the steep decline of the number density of neutral H atoms, the optical depth in the wing of the line is very low. If the amount of atomic H is not adequate to fit the observations, the fact that the transits of HD 189733b in H Lyman−α have been observed imply that external processes, such as the production of energetic neutral atoms (ENAs) as suggested by Holmström et al (2008) and Ekenbäck et al (2010), play an important role. One should also note that even in case the assumption of Koskinen et al (2010) is right, ENAs will be produced if the upper atmosphere interacts with the stellar wind plasma.…”

Section: Characterization Of the Upper Atmosphere-magnetosphere Envirmentioning

confidence: 99%

Exoplanet Upper Atmosphere Environment Characterization

et al. 2011

View full text Add to dashboard Cite

Abstract. The intense stellar SXR and EUV radiation exposure at "Hot Jupiters" causes profound responses to their upper atmosphere structures. Thermospheric temperatures can reach several thousands of Kelvins, which result in dissociation of H2 to H and ionization of H to H + . Depending on the density and orbit location of the exoplanet, as a result of these high temperatures the thermosphere expands dynamically up to the Roche lobe, so that geometric blow-off with large mass loss rates and intense interaction with the stellar wind plasma can occur. UV transit observations together with advanced numerical models can be used to gain knowledge on stellar plasma and the planet's magnetic properties, as well as the upper atmosphere.

show abstract

ENERGETIC NEUTRAL ATOMS AROUND HD 209458b: ESTIMATIONS OF MAGNETOSPHERIC PROPERTIES

Cited by 122 publications

References 46 publications

3D model of hydrogen atmospheric escape from HD 209458b and HD 189733b: radiative blow-out and stellar wind interactions

3D model of hydrogen atmospheric escape from HD 209458b and HD 189733b: radiative blow-out and stellar wind interactions

Atmospheric escape from HD 189733b observed in H I Lyman-α: detailed analysis of HST/STIS September 2011 observations

Exoplanet Upper Atmosphere Environment Characterization

Contact Info

Product

Resources

About