The Spectral Imaging CoronaGraph (SICG) obtained its first coronal image on October 25, 2023, marking the successful completion of China's first independently developed normalized operational ground-based coronagraph.

SICG, located at the Lijiang Yulong Astronomical Observatory of the Chinese Academy of Sciences with an altitude of 3200 meters, is part of the National Major Science and Technology Infrastructure “Meridian Space Weather Monitoring Project” (Chinese Meridian Project). It is jointly developed by Shandong University, Changchun Institute of Optics, Fin Mechanics and Physics, Chinese Academy of Sciences (CAS), Nanjing Institute of Astronomical Optics and Technology, CAS and Yunnan Observatory of CAS.

SICG adopts an internally occulting refractive optical system with an objective aperture of 220 mm and an observation field of 1.05 Rs to 2.00 Rs (Rs is the solar radius). It can provides observations of the coronal red line (Fe X 6374 Angstrom) and green line (Fe XIV 5303 Angstrom). After expert evaluation, the quality of scientific data obtained by SICG is of world-class standard, making it the best ground-based coronagraph currently working in this band in the entire world.

A research team led by Zhang Hongxin from Changchun Institute of Optics, Precision Mechanics and Physics has undertaken the development of the SICG coronagraph optical imaging system. This team is the first scientific research team in China to conduct coronagraph research. Due to the weak detection signal of the coronal instrument (the coronal signal intensity is one millionth of that of the sun) and the difficulty in suppressing stray light, the development of optical and mechanical systems is extremely difficult. Over the past four years, the research group has overcome numerous difficulties and ultimately complete the system development on time.

SICG is the first ground-based coronagraph in China. This achievement has successfully filled the gap in the development of coronagraphs in China and laid the foundation for the development of Solar Polar orbit space coronagraphs and L5 orbit space coronagraphs that Changchun Institute of Optics and Mechanics is striving for.

Coronal images taken on October 9 and October 23, 2023 (Image by ZHANG)

Installation and testing of SICG (Image by ZHANG)