First exoplanet transit observation with the Stratospheric Observatory for Infrared Astronomy: confirmation of Rayleigh scattering in HD 189733 b with the High-Speed Imaging Photometer for Occultations

Here, we report on the first successful exoplanettransit observation with the Stratospheric Observatoryfor Infrared Astronomy(SOFIA). We observed a single transit of the hot JupiterHD 189733 b, obtaining two simultaneous primary transit lightcurves in the B and z ′ bands as a demonstration of SOFIA’s capability to perform absolute transit photometry. We present a detailed description of our data reduction, in particular, the correlation of photometric systematics with various in-flight parameters unique to the airborne observing environment. The derived transit depths at B and z ′ wavelengths confirm a previously reported slope in the optical transmission spectrum of HD 189733 b. Our results give new insights to the current discussion about the source of this Rayleigh scatteringin the upper atmosphere and the question of fixed limb darkeningcoefficients in fitting routines.