The Lyman-alpha Solar Telescope (LST) for the ASO-S mission – III. data and potential diagnostics

Abstract

The Lyman-alpha Solar Telescope (LST) is one of the three payloads onboard the Advanced Space-based Solar Observatory (ASO-S) mission. It aims at imaging the Sun from the disk center up to 2.5 R⊙ targeting solar eruptions, particularly coronal mass ejections (CMEs), solar flares, prominences/filaments and related phenomena, as well as the fast and slow solar wind. The most prominent speciality of LST is the simultaneous observation of the solar atmosphere in both Lyα and white light (WL) with high temporospatial resolution both on the solar disk and the inner corona. New observations in the Lyα line together with traditionalWL observations will provide us with many new insights into solar eruptions and solar wind. LST consists of a Solar Corona Imager (SCI) with a field of view (FOV) of 1.1 – 2.5R⊙, a Solar Disk Imager (SDI) and a full-disk White-light Solar Telescope (WST) with an identical FOV up to 1.2R⊙. SCI has a dual waveband in Lyα (121.6 ± 10 nm) and in WL (700 ± 40 nm), while SDI works in the Lyα waveband of 121.6 ± 7.5 nm and WST works in the violet narrow-band continuum of 360 ± 2.0 nm. To produce high quality science data, careful ground and in-flight calibrations are required. We present our methods for different calibrations including dark field correction, flat field correction, radiometry, instrumental polarization and optical geometry. Based on the data calibration, definitions of the data levels and processing procedures for the defined levels from raw data are described. Plasma physical diagnostics offer key ingredients to understand ejecta and plasma flows in the inner corona, as well as different features on the solar disk including flares, filaments, etc. Therefore, we are making efforts to develop various tools to detect the different features observed by LST, and then to derive their physical parameters, for example, the electron density and temperature of CMEs, the outflow velocity of the solar wind, and the hydrogen density and mass flows of prominences. Coordinated observations and data analyses with the coronagraphs onboard Solar Orbiter, PROBA-3, and Aditya are also briefly discussed.