The Co-alignment of Winged Hα Data Observed by the New Vacuum Solar Telescope* *Supported by the National Natural Science Foundation of China.

Abstract

The New Vacuum Solar Telescope (NVST) has been releasing its novel winged Hα data (WHD) since 2021 April, namely the Hα imaging spectroscopic data. Compared with the prior released version, the new data are further co-aligned among the off-band images and packaged into a standard solar physics community format. In this study, we illustrate the alignment algorithm used by the novel WHD, which is mainly based on the optical flow method to obtain the translation offset between the winged images. To quantitatively evaluate the alignment results of two images with different similarities, we calculate the alignment accuracies between the images of different off-band and line center, respectively. The result shows that our alignment algorithm could reach up to the accuracy of about 0.″1 when the off-band of winged image is lower than 0.6 Å. In addition, we introduce the final product of the WHD in detail, which can provide convenience for the solar physicists to use high-resolution Hα imaging spectroscopic data of NVST.