Séminaire, par Nicolas Crouzet
Vendredi 19 décembre 2014, 14:30, salle des séminaires
Spectroscopic observations of exoplanets are crucial to infer the chemical compositions and physical properties of their atmospheres. In particular, spectral features can reveal the presence of molecular species and their amplitudes may constrain the presence of clouds and hazes. Some of the very first exoplanet spectra were obtained using NICMOS on board HST, and led to strong controversy in the exoplanet community. I will summarize the analysis of the gas giant planets XO-2b and XO-1b observed with NICMOS. The Wide Field Camera 3 (WFC3) on board HST now delivers hot Jupiter spectra with much higher fidelity than NICMOS had in the past. I will present near infrared observations of the canonical hot Jupiter HD 189733b obtained during a transit and during an eclipse, using the newly implemented spatial scanning mode on WFC3. Water vapor is clearly detected in the atmosphere of the planet. Consequently, we rule out an atmosphere fully obscured by high altitude clouds or hazes, and constrain the water abundance in the planet's atmosphere. A comparison with recent results obtained for other hot Jupiters using similar WFC3 data reveals that water abundances are significantly lower than predicted by planetary atmosphere models. This raises important questions on the processes involved in planet formation.
Characterizing hot Jupiter atmospheres with the Hubble Space Telescope
Spectroscopic observations of exoplanets are crucial to infer the chemical compositions and physical properties of their atmospheres. In particular, spectral features can reveal the presence of molecular species and their amplitudes may constrain the presence of clouds and hazes. Some of the very first exoplanet spectra were obtained using NICMOS on board HST, and led to strong controversy in the exoplanet community. I will summarize the analysis of the gas giant planets XO-2b and XO-1b observed with NICMOS. The Wide Field Camera 3 (WFC3) on board HST now delivers hot Jupiter spectra with much higher fidelity than NICMOS had in the past. I will present near infrared observations of the canonical hot Jupiter HD 189733b obtained during a transit and during an eclipse, using the newly implemented spatial scanning mode on WFC3. Water vapor is clearly detected in the atmosphere of the planet. Consequently, we rule out an atmosphere fully obscured by high altitude clouds or hazes, and constrain the water abundance in the planet's atmosphere. A comparison with recent results obtained for other hot Jupiters using similar WFC3 data reveals that water abundances are significantly lower than predicted by planetary atmosphere models. This raises important questions on the processes involved in planet formation.