Expected performances of the PROBA-3/ASPIICS solar coronagraph: Simulated data

Abstract

Context. The Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun (ASPIICS) is a novel externally occulted solar coronagraph that will be launched on board the Project for On-Board Autonomy (PROBA-3) mission in 2023. The external occulter will be placed on the first satellite ∼ 150 m ahead of the second satellite, which will carry an optical instrument. During 6 hours per orbit, the satellites will fly in a precise formation and will constitute a giant externally occulted coronagraph. The large distance between the external occulter and the primary objective will allow observations of the white-light solar corona starting from extremely low heights of ∼ 1.1R ⊙ . Aims. Developing and testing of algorithms for the scientific image processing requires understanding of all the optics-related and detector-related effects of the coronagraph, development of appropriate physical and numerical models, and preparation of simulated images that include all these effects. At the same time, an analysis of the simulated data gives valuable information about the performance of the instrument, the suitable observation regime, and the amount of telemetry. Methods. We used available physical models of the instrument and implemented them as a software to generate simulated data. We analyzed intermediate and complete simulated images to obtain a better understanding of the performance of ASPIICS, in particular, to predict its photometric sensitivity, effect of noise, suitable exposure times, etc. Results. The proposed models and algorithms are used not only to create the simulated data, but also to form the basis for the scientific processing algorithms to be applied during on-ground ASPIICS data processing. We discuss the possible effect of noise and the uncertainty of the calibration factors on the accuracy of final data, and propose suitable exposure times.

Simulation of inverse Fredholm reconstruction in a vignetting zone: application to ASPIICS

“…In order to derive the values of the matrix H and the straylight b for ASPIICS, we made use of the numerical model developed by Rougeot et al (2017). This approach was further used as a starting point for studies including optical defects of the coronagraph (Rougeot et al (2017); Shestov & Zhukov (2018); Rougeot et al (2019); Shestov et al (2021)).…”

“…The inversion of the Fredholm transformation has to be verified on a realistic representation of the solar corona near the limb. In their recent study, Shestov et al (2021) based their simulation on a direct image obtained during a real solar eclipse and synthetic object that present finer details than the eclipse image, Shestov et al (2019). The object used in the present study lies halfway between these two objects.…”

“…We used a solar corona picture obtained by D. Sabers, R. Royer and M. Druckmüller during the total solar eclipse of March 9, 2016 in Indonesia, where the fine details of the coronal structure have been enhanced by image processing. We impose the synthetic object to follow the dynamic range and radial decrease of intensity of the true corona, as done by Shestov et al (2021) on their synthetic image. An illustration of this object is given in Fig.…”

“…To discuss further, we now consider some "defaults" from the optics or the satellite flying formation. These aspects have been analysed by Shestov et al (2021) and Rougeot (2020). We limit here our analysis to formation flying errors and the effect of inevitable residual roughness of the optical surface of the telescope of the coronagraph.…”

“…The drawback is that this increases the blind area near the solar limb. Recent studies have envisaged observations starting at no sooner than 1.05 R or even 1.1 R , depending on the experimental parameters used, Shestov et al (2021), Rougeot (2020).…”