Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey [...] (D. K. Sing et al.)

Vol. 527
In section 10. Planets and planetary systems

Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey: detection of potassium in XO-2b from narrowband spectrophotometry

by D. K. Sing, J.-M. Désert, J. J. Fortney, et al., A&A 527, A73 alt

Spectroscopic observations of planetary transits are now almost routinely used to probe the composition of exoplanetary atmospheres: A planet appears larger at wavelengths that are more opaque to the stellar light because of the presence of an absorber in its atmosphere. Sodium was previously detected using this technique in 2002. Sing et al. present ground-based observations from the Gran Telescopio Canarias of three transits of exoplanet XO-2b to detect another alkali metal, potassium, long hypothesized to be among the most dominant of absorption sources at visible wavelengths. For the first time, they find convincing evidence of this element in the atmosphere of XO-2b, in agreement with theoretical expectations. Additional observations will be required to exclude the possibility that there were higher-than-usual activity levels during the observations. These might have affected both the inferred radii and spectroscopic interpretation because the measurements were not simultaneous, but this is unlikely given the very low activity level of star XO-2.