Author/s: G. Chen, E. Pallé, L. Nortmann, F. Murgas, H. Parviainen, G. Nowak
Reference: 2017 A&A 600 L11 | Link
The atmospheres of exoplanets is a unique window to reveal the nature of alien worlds. When a planet transits its host star, transmission spectroscopy can be employed to know the composition of planetary atmospheres by measuring the planet size at different wavelengths. In the optical wavelengths, the sodium (Na) doublet at 589 nm and the potassium (K) doublet at 768 nm are two of the most important opacity sources for such kind of atmospheric characterization; e.g., they provide important information of the temperature profile. We report the first detection of sodium absorption in the atmosphere of the hot Jupiter WASP-52b. We observed one transit of WASP-52b with the low-resolution Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the 10.4 m Gran Telescopio Canarias (GTC). The resulting transmission spectrum, covering the wavelength range from 522 nm to 903 nm, is flat and featureless, except for the significant narrow absorption signature at the sodium doublet, which can be explained by an atmosphere in solar composition with clouds at 1 mbar. A cloud-free atmosphere is stringently ruled out. By assessing the absorption depths of sodium in various bin widths, we find that temperature increases towards lower atmospheric pressure levels, with a positive temperature gradient of 0.88 ± 0.65 K/km. This possibly indicates that heating processes and a temperature inversion exist in the upper atmosphere.