Lyman-alpha Solar Telescope Research Articles

Sympathetic solar eruption on 2024 February 9

Abstract In this paper, we perform a follow-up investigation of the solar eruption originating from active region (AR) 13575 on 2024 February 9.
The primary eruption of a hot channel (HC) generates an X3.4 class flare, a full-halo coronal mass ejection (CME), and an extreme-ultraviolet (EUV) wave.
Interaction between the wave and a quiescent prominence (QP) leads to a large-amplitude, transverse oscillation of QP.
After the \textbf{transverse} oscillation, QP loses equilibrium and rises up.
The ascending motion of the prominence is coherently detected and tracked up to $\sim$1.68 $R_{\odot}$ by the Solar UltraViolet Imager (SUVI) onboard the GOES-16 spacecraft
and up to $\sim$2.2 $R_{\odot}$ by the Solar Corona Imager (SCI\_UV) of the Lyman-alpha Solar Telescope (LST) onboard the ASO-S spacecraft.
The velocity increases linearly from 12.3 to 68.5 km s$^{-1}$ at 18:30 UT.
The sympathetic eruption of QP drives the second CME with a typical three-part structure. 
The bright core comes from the eruptive prominence, which could be further observed up to $\sim$3.3 $R_{\odot}$ 
by the Large Angle Spectroscopic Coronagraph (LASCO) onboard the SOHO mission.
The leading edge of the second CME accelerates continuously from $\sim$120 to $\sim$277 km s$^{-1}$.
The EUV wave plays an important role in linking the primary eruption with the sympathetic eruption.

Inflight Performance and Calibrations of the Lyman-Alpha Solar Telescope on Board the Advanced Space-Based Solar Observatory

Inflight Performance and Calibrations of the Lyman-Alpha Solar Telescope on Board the Advanced Space-Based Solar Observatory

A Statistical Study of Solar White-Light Flares Observed by the White-Light Solar Telescope of the Lyman-Alpha Solar Telescope on the Advanced Space-Based Solar Observatory (ASO-S/LST/WST) at 360 nm

Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from October 2022 to May 2023 and identify 49 WLFs at 360 nm from WST observations, i.e. with an occurrence rate of 23.9%. The percentages of WLFs for M1 – M4 (31 out of 180), M5 – M9 (11 out of 18), and above X1 (7 for all) flares are 17.2%, 61.1%, and 100%, respectively, namely the larger the flares, the more likely they are WLFs at 360 nm. We further analyze 39 WLFs among the identified WLFs and investigate their properties such as white-light enhancement, duration, and brightening area. It is found that the relative enhancement of the white-light emission at 360 nm is mostly (>90%) less than 30% and the mean enhancement is 19.4%. The WLFs’ duration at 360 nm is mostly (>80%) less than 20 minutes and its mean is 10.3 minutes. The brightening area at 360 nm is mostly (>75%) less than 500 arcsecond2 and the median value is 225. We find that there exist good correlations between the white-light enhancement/duration/area and the peak soft X-ray (SXR) flux of the flare, with correlation coefficients of 0.68, 0.58, and 0.80, respectively. In addition, the white-light emission in most WLFs peaks around the same time as the temporal derivative of SXR flux as well as the hard X-ray emission at 20 – 50 keV, indicative of the Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations.

Intelligent sensitivity analysis framework based on machine learning for spacecraft thermal design

The variance-based method of global sensitivity analysis (GSA) has been widely applied in spacecraft thermal design, which is typically calculated using Monte Carlo estimations. However, such estimations require a large number of samples to ensure sufficient accuracy, which makes GSA expensive to perform when modeling is difficult. Moreover, multimodal or highly skewed output distributions may result in the use of variance as an uncertain agent that generates contradictory results. Therefore, an intelligent density-based GSA framework based on machine learning and multi-fidelity metamodels called IDGSA-3M is proposed. An intelligent batch processing system based on a real-time data interaction between MATLAB and NX/TMG was designed that uses many cheap low-fidelity sample points to reduce the cost of model evaluation while using a small number of expensive high-fidelity sample points to maintain high accuracy, thus achieving trade-offs between high accuracy and low computational cost. A radial basis function (RBF) neural network based on an improved mind evolutionary algorithm was applied to approximate the multi-fidelity metamodel of a spacecraft thermophysical model calculated using a batch processing system, which had a computational speed that was 1000+ times faster than that of the traditional thermophysical model and a high computational accuracy of 99%+. The output distributions of the RBF were then characterized by its cumulative distribution functions to obtain density-based sensitivity indices. Both the theoretical and experimental results of GSA for the thermal design parameters of the extreme ultraviolet radiation detector on the space-based Lyman-Alpha Solar Telescope, developed in China, demonstrated that the convergence rate of IDGSA-3M can be improved up to 10-fold for a fixed convergence level in comparison with two other GSA methods, thereby verifying its superiority.

Methodology for in-flight flat-field calibration of the Lyman-alpha solar telescope (LST)

Flat-field reflects the non-uniformity of the photometric response at the focal plane of an instrument, which uses digital image sensors, such as Charge Coupled Device (CCD) and Complementary Metal-Oxide-Semiconductor (CMOS). This non-uniformity must be corrected before being used for scientific research. In this paper, we assess various candidate methods via simulation using available data so as to figure the in-flight flat-field calibration methodology for the Lyman-alpha Solar Telescope (LST). LST is one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission and consists of three instruments: a White-light Solar Telescope (WST), a Solar Disk Imager (SDI) and a dual-waveband Solar Corona Imager (SCI). In our simulations, data from the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) mission are used. Our results show that the normal KLL method is appropriate for in-flight flat-field calibration of WST and implementing a transmissive diffuser is applicable for SCI. For the in-flight flat-field calibration of SDI, we recommend the KLL method with off-pointing images with defocused resolution of around 18″, and use the local correlation tracking (LCT) algorithm instead of limb-fitting to determine the relative displacements between different images.

Thermal control of primary mirror of Space Solar Telescope

The space-based Lyman-alpha Solar Telescope (LST) developed by China will conduct in-depth observation and research on solar activity and internal dynamics of the sun. Thermal control of the primary mirror is the core of the LST and ensures normal and efficient operation of the LST primary mirror. The primary mirror directly receives solar energy. Its element is produced from fused silica, and the multilayer coatings have high heat absorption. The primary mirror is connected with the front of the piezoelectric actuator for high-frequency image stabilization. According to these characteristics, we study the thermal properties of the primary mirror by attaching a high-thermal-conductivity graphite membrane to its back and connecting the annular bracket. We conduct a thermal equilibrium test and finite element network simulation in high-temperature mode, and their results differ by < 1 °C. High- and low-temperature simulations of the primary mirror in orbital operation show that it meets the thermal control target of < 40 °C. Therefore, applying a graphite membrane to the LST primary mirror well meets the needs of thermal control. This provides a theoretical basis for improving the reliability and thermal optimization of the primary mirror.

The Trigger and Termination Scheme for the Event Mode of the Lyman-alpha Solar Telescope (LST) onboard the ASO-S Mission

The Advanced Space-based Solar Observatory (ASO-S) is the China's first comprehensive solar dedicated satellite, scheduled to be launched around 2022. The Lyman-alpha (Lyα) Solar Telescope (LST) is one of the payloads of the ASO-S, consisting of three scientific instruments and two Guide Telescopes (GTs). The scientific instruments include a Solar Disk Imager (SDI), a White-light Solar Telescope (WST), and a Solar Corona Imager (SCI), which are aimed to observe the whole evolving process of two types of violent eruptions on the Sun, i.e., solar flares and coronal mass ejections, in multiwavelengths with high temporal and spatial resolutions. To achieve this goal, all LST instruments have included an observation mode (event mode) dedicated to event observations. In this mode, all instruments take images at a higher cadence (the SCI takes full-frame coronal images while SDI and WST take only partial frame images around the eruption region). The time and location information of the eruption events can be effectively obtained by monitoring the local brightness enhancement of the onboard images processed with median filtering and pixel rebinning. The obtained information will provide an important electronic input for the automatic switching between different observation modes of LST.

Automatic Coronagraph Image Classification with Machine Learning Methods

The detection of Coronal Mass Ejections (CMEs) is an important prerequisite for establishing a CME event database and realizing the prediction of CME interplanetary propagation. The Lyman-alpha Solar Telescope (LST) aboard the ASO-S (Advanced Space-based Solar Observatory) satellite will be equipped with a white-light coronagraph. The images with CME detected will be contributed to various space weather prediction centers in China for CME early warning. The Visual Geometry Group (VGG) 16 convolutional neural network method is applied by us to automatically and effectively classify coronagraph images. Firstly, based on the image of the white light coronagraph of Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2, we labeled the images according to whether a CME is observed. Then, the data set was used for training the VGG model. We find that the accuracy of the model in the test set classification reaches 92.5%. Next, according to the obtained classification results and combined with the space-time continuity rules, we corrected the mislabeling of images, and derived our final CME image sequences. Compared with the manual CME catalog of Coordinated Data Analysis Workshops (CDAW), the classified CME image sequences can include CME data more completely, and have higher detection sensitivity for weak CME structures.

Environmental tests of the HXI spectrometer for the ASO-S mission

The Advanced Space-based Solar Observatory (ASO-S) is the first Chinese solar mission and is scheduled to be launched in 2022. It is designed to study the solar magnetic field, coronal mass ejections, solar flares, and their relationships. The ASO-S includes three scientific payloads: the Full-disk vector MagnetoGraph, the Lyman-alpha Solar Telescope and the Hard X-ray Imager. As a key part onboard the ASO-S, the HXI will improve our understanding of solar flares during the 25th solar maximum. The HXI comprises three parts, namely a collimator (HXI-C), a spectrometer (HXI-S) and an electronics control box (HXI-E). Extensive environmental tests, such as mechanical and thermal tests are important for a space mission to ensure the design and performance are suitable for the severe challenges presented by the launch and on-orbit operations. This paper describes the procedures and results of environmental tests performed on the qualification model of the HXI-S. Functional tests of the spectrometer are reported as well. Test results show that the current qualification model fully satisfies mission requirements.

Space Weather Related to Solar Eruptions With the ASO-S Mission

The Advanced Space-based Solar Observatory (ASO-S) is a mission aiming at exploring solar flares, coronal mass ejections (CMEs), solar magnetic field and their relationships. To fulfill its major scientific objectives, ASO-S has three elaborately-designed payloads onboard: the Full-disk vector MagnetoGraph (FMG), the Lyman-alpha Solar Telescope (LST), and the Hard X-ray Imager (HXI) dedicated to observe vector magnetic fields, CMEs, and flares, respectively. Beside the scientific objectives, we have an operational objective to observe solar eruptions and magnetic field for making related space weather forecasts. More specifically, we have set a priority for the downlink of CME data observed by LST, and will distribute those data to different space weather prediction centers in China within two hours once the Science Operation and Data Center (SODC) of ASO-S receive the data. After data downlink and archiving, different automatic detection, tracking, and cataloguing procedures are planned to run for the most critical solar eruptive features. On the other hand, based on the distributed and downloaded data, different space weather prediction centers are to activate their forecast systems for the ASO-S observed solar eruption events. Our particular interests are currently focused on nowcast of different eruption events, prediction of CME arrivals, forecast of solar flares and the onset of solar eruptions. We are also working on further forecast potentials using the ASO-S data to make contributions to other possible important issues of space weather.

The Lyman-alpha Solar Telescope (LST) for the ASO-S mission – II. design of LST

As one of the three payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Lyα) Solar Telescope (LST) is composed of three instruments: a Solar Corona Imager (SCI), a Lyα Solar Disk Imager (SDI) and a full-disk White-light Solar Telescope (WST). When working in-orbit, LST will simultaneously perform high-resolution imaging observations of all regions from the solar disk to the inner corona up to 2.5 R⊙ (R⊙ stands for the mean solar radius) with a spatial resolution of 4.8″ and 1.2″ for coronal and disk observations, respectively, and a temporal resolution of 30 – 120 s and 1 – 120 s for coronal and disk observations, respectively. The maximum exposure time can be up to 20 s due to precise pointing and image stabilization function. Among the three telescopes of LST, SCI is a dual-waveband coronagraph simultaneously and independently observing the inner corona in the HI Lyα (121.6±10 nm) line and white light (WL) (700±40 nm) wavebands by using a narrowband Lyα beam splitter and has a field of view (FOV) from 1.1 to 2.5 R⊙. The stray-light suppression level can attain <10−6 B⊙ (B⊙ is the mean brightness of the solar disk) at 1.1 R⊙ and ≤5×10−8 B⊙ at 2.5 R⊙. SDI and WST are solar disk imagers working in the Lyα line and 360.0 nm wavebands, respectively, which adopt an off-axis two-mirror reflective structure with an FOV up to 1.2 R⊙, covering the inner coronal edge area and relating to coronal imaging. We present the up-to-date design for the LST payload.

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

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.

On the error analyses of polarization measurements of the white-light coronagraph aboard ASO-S

The Advanced Space-based Solar Observatory (ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections (CMEs), and their magnetism. For the study of CMEs, the payload Lyman-alpha Solar Telescope (LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial for deriving fundamental physical parameters of CMEs. To make such measurements, there are two options for a Stokes polarimeter which have been applied by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizer, the other involves both a half-wave plate and a linear polarizer.We find that the former option is subject to less uncertainty in the derived Stokes vector propagating from detector noise. The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembly in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer.

Design of First-Order 121.6 nm Minus Filters.

The equivalent parameters function in Macleod software can be used to calculate the equivalent admittance and phase thickness of multilayers, even when the material is both absorbing and dispersive, and the incidence angle is non-zero. We utilized this software to design first-order 121.6 nm minus filters based on a lanthanum trifluoride (LaF3)/magnesium fluoride (MgF2) multilayer; a Gaussian-type target curve was also introduced into the design. Minus filters with bandwidths of 10 and 5 nm were obtained and had good visible light suppression and low side-lobe ripples. This designed filter will be fabricated for use in a Lyman-alpha coronagraph and imager installed in the Lyman-Alpha Solar Telescope, which will be launched by China in 2021.

Design of second-order 121.6-nm narrowband minus filters using asymmetrically apodized thickness modulation

An asymmetrically apodized thickness modulation design method is proposed to design second-order narrowband minus filters at 121.6 nm. The sine-wave, linear, quintic functions are used as amplitude envelope to apodize the thickness modulation design. LaF3/MgF2 minus filters at 121.6 nm with a bandwidth of 5 nm are obtained. This designed filter will be fabricated for utilizing in Lyman-alpha coronagraph and imager installed in Lyman-alpha Solar Telescope, which will be launched by China in 2021.