The wind-driven halo in high-contrast images I: analysis from the focal plane images of SPHERE

Faustine Cantalloube (1) , Ollie J. D. Farley (2) , Julien Milli (3, 4) , Nazim Ali Bharmal (2) , Wolfgang Brandner (1) , Carlos Correia (5, 6) , Kjetil Dohlen (5) , Thomas Henning (1) , James Osborn (2) , Emiel Por (7) , Marcos Suárez (8) , Arthur Vigan (5)

1 MPIA - Max-Planck-Institut für Astronomie
2 Department of Physics [Durham]
3 ESO - European Southern Observatory [Santiago]
4 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
5 LAM - Laboratoire d'Astrophysique de Marseille
6 W.M. Keck Observatory
7 Leiden Observatory [Leiden]
8 ESO - European Southern Observatory

Context. The wind driven halo is a feature observed within the images delivered by the latest generation of ground-based instruments equipped with an extreme adaptive optics system and a coronagraphic device, such as SPHERE at the VLT. This signature appears when the atmospheric turbulence conditions are varying faster than the adaptive optics loop can correct. The wind driven halo shows as a radial extension of the point spread function along a distinct direction (sometimes referred to as the butterfly pattern). When present, it significantly limits the contrast capabilities of the instrument and prevents the extraction of signals at close separation or extended signals such as circumstellar disks. This limitation is consequential because it contaminates the data a substantial fraction of the time: about 30% of the data produced by the VLT/SPHERE instrument are affected by the wind driven halo. Aims. This paper reviews the causes of the wind driven halo and presents a method to analyze its contribution directly from the scientific images. Its effect on the raw contrast and on the final contrast after post-processing is demonstrated. Methods. We used simulations and on-sky SPHERE data to verify that the parameters extracted with our method are capable of describing the wind driven halo present in the images. We studied the temporal, spatial and spectral variation of these parameters to point out its deleterious effect on the final contrast. Results. The data driven analysis we propose does provide information to accurately describe the wind driven halo contribution in the images. This analysis justifies why this is a fundamental limitation to the final contrast performance reached. Conclusions. With the established procedure, we will analyze a large sample of data delivered by SPHERE in order to propose, in the future, post-processing techniques tailored to remove the wind driven halo.

Mots clés: Atmospheric effects; Planet-disk interactions; Instrumentation: adaptive optics; Instrumentation: high angular resolution; Infrared: planetary systems; Techniques: image processing

Domaines: Instrumentation et méthodes pour l'astrophysique [astro-ph.IM]

Faustine Cantalloube, Ollie J. D. Farley, Julien Milli, Nazim Ali Bharmal, Wolfgang Brandner, et al.. The wind-driven halo in high-contrast images I: analysis from the focal plane images of SPHERE. Astronomy and Astrophysics - A&A, 2020, ⟨10.1051/0004-6361/201937397⟩. ⟨hal-02504683⟩