Vol. 554
In section 10. Planets and planetary systems

Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b

by R.J. de Kok, M. Brogi, I.A.G. Snellen, J. Birkby, S. Albrecht, and E.J.W. de Mooij A&A 554, A82


Because it transits its very bright parent star, HD 189733b is one of the most studied exoplanets. Using the CRIRES infrared spectrograph on the VLT at 2.0 and 2.3 microns, de Kok et al. searched for the Doppler-shifted signatures of CO, H2O, CH4, and CO2 absorption in the tiny planetary contribution to the integrated light of the HD 189733 system. They did not find any sign of H2O, CH4, or CO2, but a significant 5-sigma absorption signal from CO. CO must be present above the haze that has been proposed to explain the visible and infrared spectrum of the planet, either because CO is abundant or because the haze is optically thin at normal incidence. The Doppler-shift of the CO line provides a model-independent measurement of the stellar and planetary masses. The technique thus powerfully characterizes the atmosphere of the planet and constrains the masses of the planet and its star.