Exoplanet characterization using angular and spectral differential imaging

In the near future, new high-contrast imaging instruments dedicated to the direct detection of exoplanets at large orbital separations will be installed at the focus of large ground-based telescopes. Data obtained with these instruments optimized for very high contrast are strongly limited by the speckle noise. Specific observing strategies and data analysis methods, such as angular and spectral differential imaging, are required to attenuate the noise level and possibly detect the faint planet flux. Even though these methods are very efficient at suppressing the speckles, the photometry of the faint planets is dominated by the speckle residuals and it has a direct impact on the determination of the physical parameters of the detected planets. We present here the simulations that have been performed in the context of IRDIS, the dual-band imager of VLT-SPHERE, to estimate the influence of the photometric error on exoplanet characterization. In particular we show that the expected photometric performances will allow the detection and characterization of exoplanets down to the Jupiter mass at angular separations of 1.0” and 0.2” respectively around high mass and low mass stars with 2 observations in different filter pairs. We also show that the determination of the planets physical parameters from photometric measurements in different filter pairs is essentially limited by the error on the determination of the surface gravity.