Influence of stellar variability on the determination of the radius during a transit of an exoplanet

Abstract

Stellar variability can affect the estimate of an exoplanet radius measured during a transit. We developed a transit light curve model which includes stellar spots. It appears that, if spectro-photometric technique is used, spots and faculae have to be considered to conclude on atmospheric detection and characterization. When using a model including spots, characterization of Hot-Jupiter atmosphere around active stars is possible with this technique, provided a signal to noise ratio up to 105. For Earth-size planets a long-term parallel photometric follow up monitoring the stellar activity is required to compensate the error due to the stellar variability.