Transmission spectroscopy during planetary transits is a powerful technique to explore exoplanetary atmospheres. It consists in measuring the variations of the planet-to-star radius ratio as a function of wavelength. One of the main limitation of this technique is stellar activity, which is usually taken into account only by assessing the effect of non-occulted stellar spots on the planet-to-star radius estimation. In this talk, I present our recent study on the impact of the occultation of stellar active regions, such as spots and plages, on the transmission spectra of transiting exoplanets. We found that the anomalies inside the transit light curve can lead to a significant underestimation or overestimation of the planet-to-star radius ratio as a function of wavelength. At short wavelengths, the effect can reach up to a maximum difference of 10% in the planet-to-star radius ratio, mimicking the signature of light scattering in the planetary atmosphere. Atmospheric scattering has been proposed to interpret the increasing slopes of transmission spectra toward the blue for exoplanets HD 189733b and GJ 3470b. We showed that these signatures can be alternatively interpreted by stellar activity, if the planets transit across stellar plages with sun-like properties.
2014 May 15, 13:30
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto