deep PACO: Combining statistical models with deep learning for exoplanet detection and characterization in direct imaging at high contrast

International audienceDirect imaging is an active research topic in astronomy for the detection and the characterization of young sub-stellar objects. The very high contrast between the host star and its companions makes the observations particularly challenging. In this context, post-processing methods combining several images recorded with the pupil tracking mode of telescope are needed. In previous works, we have presented a data-driven algorithm, PACO, capturing locally the spatial correlations of the data with a multivariate Gaussian model. PACO delivers improved detection sensitivity and confidence, as well as more accurate astro-photometric estimates than the standard post-processing methods of the field. However, there is room for improvement due to the approximate fidelity of the PACO statistical model to the time evolving observations. In this paper, we propose to combine the statistical model of PACO with supervised deep learning. The data are first pre-processed with the PACO framework to improve the stationarity and the contrast. A convolutional neural network (CNN) is then trained in a supervised fashion to detect the residual signature of synthetic sources. Finally, the trained network delivers a detection map. The photometry of detected sources is estimated by a second CNN. Both models are trained from scratch with custom data augmentation strategies allowing the creation of large training sets from a single spatio-temporal dataset. We apply the proposed approach to several datasets from the infrared imager of the VLT/SPHERE instrument. Our results show that its detection stage performs significantly better than baseline methods of the fields (cADI, PCA), and leads to a contrast improvement up to half a magnitude compared to PACO. The characterization stage of the proposed method performs on average on par with or better than the comparative algorithms (PCA, PACO) for angular separation above 0.5 arcsec. A typical reduction of the absolute error of photometric estimation by a factor two is obtained for sources of contrast up to 10 −6. Closer to the star, PCA and PACO remain slightly better. For both stages, controlling the uncertainty and the data-dependence of the current models remains an important avenue for improvement