Optimal stereoscopic angle for 3D reconstruction of synthetic small-scale coronal transients using the CORAR technique

Context. In previous studies, we applied the CORrelation-Aided Reconstruction (CORAR) technique to reconstruct three-dimensional (3D) structures of transients in the field of view (FOV) of Heliospheric Imager-1 (HI-1) on board the spacecraft STEREO-A/B. The reconstruction quality depends on the stereoscopic angle ( θ Sun ), that is, the angle between the lines connecting the Sun and two spacecraft. Aims. To apply the CORAR technique on images from the coronagraphs COR-2 on board STEREO, the impact of θ Sun on the reconstruction of coronal transients should be explored, and the optimal θ Sun for reconstruction should be found. Methods. We apply the CORAR method on synthetic COR-2 images containing the small-scale transient, namely the blob, in the case of various θ Sun . Based on a comparison of the synthetic blob and the corresponding reconstructed structure in location and 3D shape, we assess its level of reconstruction quality. According to the reconstruction-quality levels of blobs in various positions with various attributes, we evaluate the overall performance of reconstruction in the COR-2 FOV to determine the optimal θ Sun for reconstruction. Results. In the case of θ Sun > 90°, we find that the range of suitable θ Sun , in which the small-scale transients in the COR-2 FOV typically have high reconstruction quality, is between 120° and 150°, and the optimal θ Sun for reconstruction is close to 135°. In the case of θ Sun < 90°, the global reconstruction performance is similar to that of (180° − θ Sun ). We also discuss the spatial factors in determining the range of suitable θ Sun , and study the influence of blob properties on the reconstruction. Our work can serve as a foundation for the design of future missions containing coronagraphs from multiple perspectives, such as the newly proposed SOlar Ring mission (SOR).