Photometric characterization of exoplanet using angular and spectral differential imaging in SPHERE/IRDIS


A. Vigan (1), C. Moutou (1), M. Langlois (2), F. Allard (2), A. Boccaletti (3), M. Carbillet (4), D. Mouillet (5), I. Smith (4)


(1) Laboratoire d’Astrophysique de Marseille; (2) Centre de Recherche Astrophysique de Lyon; (3) Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique; (4) Laboratoire Fizeau; (5) Laboratoire d’Astrophysique de l’Observatoire de Grenoble


Direct detection and characterization of exoplanets with ground based telescope is one of the next important steps for a better understanding the formation and evolution of planetary systems, as well as the internal structure of large gaseous planets. Several instruments are currently being built to perform high angular and high contrast imaging from the ground thanks to the use of extreme AO systems and efficient coronagraphs. The data obtained with these future instruments optimized for direct detections will be strongly limited by the speckle noise. Specific observing strategies and data analysis methods, such as angular and spectral differential imaging, will be 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 still dominated by the speckle residuals. The determination of the physical parameters of the detected planets such as effective temperature (Teff) and surface gravity (log g) by comparison of photometric measurements to planetary atmosphere models is then limited by the photometric error on the planet flux. In the context of the preparation of SPHERE, the planet finder for the VLT, and its dual-band imager IRDIS, we have investigated this photometric error and the impact on the determination of the detected planets physical parameters. We present here the detailed end-to-end simulations that were performed with the CAOS-based Software Package for SPHERE to obtain realistic data representing typical observations with IRDIS. The simulated data are used to measure the photometric accuracy as a function of contrast and wavelength for planets detected with angular and spectral+angular differential methods. We then used this empirical accuracy to study the characterization capabilities of IRDIS in Dual Band Imaging mode. 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.

Attached documents

Lyot2010proc s7 talk ViganA.pdf
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