arXiv subjects

Dechao Song

Publications and source records attributed to Dechao Song.

10 recordsLinked to original sources

arXiv2026

Quadrupole White-light Sources in an X1.2 Flare Observed by ASO-S/LST/WST and SDO/HMI

We present observations of an X1.2 white-light flare on 2023 January 6, which exhibits a rare quadrupolar white-light source configuration. This event was observed by the White-light Solar Telescope (WST; 3600 \AA) aboard the Advanced Space-based Solar Observatory and the Helioseismic and Magnetic Imager (HMI; 6173 \AA) aboard the Solar Dynamics Observatory. Four flare-related footpoints (labeled as FP1--FP4) were nearly simultaneously identified in both WST 3600 \AA\ and HMI 6173 \AA\ continua, associated with a quadrupolar magnetic configuration and a failed filament eruption. The inner sources of FP1 and FP2 showed a similar enhancement of $\sim$65%/10% in the WST/HMI continuum, while the outer sources of FP3 and FP4 exhibited weaker responses. The inner footpoints had earlier responses in UV and EUV bands and were spatially coincident with the hard X-ray (HXR) footpoint sources. The two southern footpoints (FP2 and FP4) showed stronger HXR and white-light emissions than their northern counterparts (FP1 and FP3), with FP4 uniquely exhibiting a distinct HXR emission above 60 keV, in contrast to the absence of such an emission at FP3. Notably, faint WST 3600 \AA\ enhancements at FP4 were observed during the gradual phase, temporally consistent with the fallback of filament material. This X1.2 flare presents a novel quadrupolar white-light structure, enriching our understanding of the generation and evolution of white-light flares.

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arXiv2026

Revisiting Approaches to Stellar White-Light Flare Energy Based on Spatiotemporally Resolved Solar Observations

Accurately estimating the bolometric energy of solar and stellar white-light flares (WLFs) is crucial for understanding their physical nature and impact on surrounding planets. However, the lack of spatial resolution in stellar observations forced pioneering stellar WLF studies to adopt simplified energy estimation methods, typically assuming either a constant flare temperature or a fixed radiating area. To assess the physical plausibility of these assumptions, we utilize high-spatiotemporal-resolution solar observations to analyze the true evolution of source region's radiating area and temperature of 70 solar WLFs. It is revealed that both area and temperature of most solar WLFs undergo significant temporal evolution, and the flare area strongly correlates with the flare's peak optical continuum flux. Therefore, we propose a new energy estimation method that permits both flare area and temperature to evolve. Compared with existing methods, our dynamic approach yields systematically lower flare energies, which then prompts us to revisit classical macroscopic scaling laws related to the flare energy. It is further revealed that different energy estimation approaches can systematically alter these scaling relations, calling for a re-examination of these established statistical results and their targeted testing or revision in future work.

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arXiv2025

Magnetic Field Configuration of a Quiescent Prominence Revealed by Large-amplitude Longitudinal Oscillations in End-view Observations

Prominence seismology, applied to the large-amplitude longitudinal oscillation, is used to indirectly diagnose the geometry and strength of the magnetic fields inside the prominence. In this paper, combining imaging and spectroscopic data, the magnetic field configuration of a quiescent prominence is revealed by large-amplitude longitudinal oscillations observed in end view on 2023 December 4. Particularly, the prominence oscillation involved blueshift velocities in Dopplergrams and horizontal motions in extreme-ultraviolet (EUV) images. Originally, the prominence oscillation was triggered by the collision and heating of an adjoining hot structure associated with two coronal jets. The oscillation involved two groups of signals with similar oscillatory parameters, a three-dimensional (3D) initial amplitude of 40 Mm and a 3D velocity amplitude of 48 km/s, both lasting for 4 cycles with a period of 77 minutes, with a phase difference of pi/4. While the angle between 3D velocities and the prominence axis ranges from 10 to 30. Two methods, utilizing time-distance diagrams and velocity fields, are employed to calculate the curvature radius of magnetic dips supporting the prominence materials. Both methods yield similar value ranges and trends from the bottom to the top of magnetic dips, with the curvature radius increasing from 90 Mm to 220 Mm, then decreasing to 10 Mm, with transverse magnetic field strength 25 Gauss. From this, the realistic 3D geometry of the prominence magnetic dips is determined to be sinusoidal. To the best of our knowledge, we present the first accurate calculation of the 3D curvature radius and geometry of the prominence magnetic dips based on longitudinal oscillatory motions.

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arXiv2024

Improving image quality of the Solar Disk Imager (SDI) of the Lyman-alpha Solar Telescope (LST) onboard the ASO-S mission

The in-flight calibration and performance of the Solar Disk Imager (SDI), which is a pivotal instrument of the Lyman-alpha Solar Telescope (LST) onboard the Advanced Space-based Solar Observatory (ASO-S) mission, suggested a much lower spatial resolution than expected. In this paper, we developed the SDI point-spread function (PSF) and Image Bivariate Optimization Algorithm (SPIBOA) to improve the quality of SDI images. The bivariate optimization method smartly combines deep learning with optical system modeling. Despite the lack of information about the real image taken by SDI and the optical system function, this algorithm effectively estimates the PSF of the SDI imaging system directly from a large sample of observational data. We use the estimated PSF to conduct deconvolution correction to observed SDI images, and the resulting images show that the spatial resolution after correction has increased by a factor of more than three with respect to the observed ones. Meanwhile, our method also significantly reduces the inherent noise in the observed SDI images. The SPIBOA has now been successfully integrated into the routine SDI data processing, providing important support for the scientific studies based on the data. The development and application of SPIBOA also pave new ways to identify astronomical telescope systems and enhance observational image quality. Some essential factors and precautions in applying the SPIBOA method are also discussed.

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arXiv2024

Inflight Performance and Calibrations of the Lyman-alpha Solar Telescope on board the Advanced Space-based Solar Observatory

The Lyman-alpha Solar Telescope (LST) on board the Advanced Space-based Solar Observatory (ASO-S) is the first payload to image the full solar disk and the solar corona in both white-light (WL) and ultraviolet (UV) H I Lya, extending up to 2.5 solar radii (Rs). Since the launch of the ASO-S on 9 October 2022, LST has captured various significant solar activities including flares, prominences, coronal mass ejections (CMEs). LST covers different passbands of 121.6 nm, 360 nm and 700 nm. The Lya Solar Disk Imager (SDI) has a field of view (FOV) of 38.4 arcmin and a spatial resolution of around 9.5 arcsec, while the White-Light Solar Telescope (WST) has a FOV of 38.43 arcmin and a spatial resolution of around 3.0 arcsec. The FOV of the Lya Solar Corona Imager (SCI) reaches 81.1 arcmin and its spatial resolution is 4.3 arcsec. The stray-light level in the 700 nm waveband is about 7.8e-6 MSB (mean solar brightness) at 1.1 Rs and 7.6e-7 MSB at 2.5 Rs, and in the Lya waveband it is around 4.3e-3 MSB at 1.1 Rs and 4.1e-4 MSB at 2.5 Rs. This article will detail the results from on-orbit tests and calibrations.

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arXiv2024

Association between a Failed Prominence Eruption and the Drainage of Mass from Another Prominence

Sympathetic eruptions of solar prominences have been studied for decades, however, it is usually difficult to identify their causal links. Here we present two failed prominence eruptions on 26 October 2022 and explore their connections. Using stereoscopic observations, the south prominence (PRO-S) erupts with untwisting motions, flare ribbons occur underneath, and new connections are formed during the eruption. The north prominence (PRO-N) rises up along with PRO-S, and its upper part disappears due to catastrophic mass draining along an elongated structure after PRO-S failed eruption. We suggest that the eruption of PRO-S initiates due to a kink instability, further rises up, and fails to erupt due to reconnection with surrounding fields. The elongated structure connecting PRO-N overlies PRO-S, which causes the rising up of PRO-N along with PRO-S and mass drainage after PRO-S eruption. This study suggests that a prominence may end its life through mass drainage forced by an eruption underneath.

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arXiv2024

Spectral and Imaging Observations of a C2.3 White-Light Flare from the Advanced Space-Based Solar Observatory (ASO-S) and the Chinese H$\alpha$ Solar Explorer (CHASE)

Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (say X- and M-class flares). Here we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the \emph{Advanced Space-based Solar Observatory} and the \emph{Chinese H$\alpha$ Solar Explorer}. This flare exhibits an increase of $\approx$6.4\% in the photospheric Fe \textsc{i} line at 6569.2\,\AA\ and {$\approx$3.2\%} in the nearby continuum. The continuum at 3600\,\AA\ also shows an enhancement of $\approx$4.7\%. The white-light brightening kernels are mainly located at the flare ribbons and co-spatial with nonthermal hard X-ray sources, which implies that the enhanced white-light emissions are related to nonthermal electron-beam heating. At the brightening kernels, the Fe \textsc{i} line displays an absorption profile that has a good Gaussian shape, with a redshift up to $\approx$1.7 km s$^{-1}$, while the H$\alpha$ line shows an emission profile though having a central reversal. The H$\alpha$ line profile also shows a red or blue asymmetry caused by plasma flows with a velocity of several to tens of km s$^{-1}$. It is interesting to find that the H$\alpha$ asymmetry is opposite at the conjugate footpoints. It is also found that the CHASE continuum increase seems to be related to the change of photospheric magnetic field. Our study provides comprehensive characteristics of a small white-light flare that help understand the energy release process of white-light flares.

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arXiv2024

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 Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations.

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arXiv2022

Statistical analysis of circular-ribbon flares

Circular-ribbon flares (CFs) are a special type of solar flares owing to their particular magnetic topology. In this paper, we conducted a comprehensive statistical analysis of 134 CFs from 2011 September to 2017 June, including four B-class, 82 C-class, 40 M-class, and eight X-class flares, respectively. The flares were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft. The physical properties of CFs are derived, including the location, area ($A_{CF}$), equivalent radius ($r_{CF}$) assuming a semi-spherical fan dome, lifetime ($\tau_{CF}$), and peak SXR flux in 1$-$8 {\AA}. It is found that all CFs are located in active regions, with the latitudes between -30$^\circ$ and 30$^\circ$. The distributions of areas and lifetimes could be fitted with a log-normal function. There is a positive correlation between the lifetime and area. The peak SXR flux in 1$-$8 {\AA} is well in accord with a power-law distribution with an index of $-$1.42. For the 134 CFs, 57\% of them are accompanied by remote brightenings or ribbons. A positive correlation exists between the total length ($L_{RB}$) and average distance ($D_{RB}$) of remote brightenings. About 47\% and 51\% of the 134 CFs are related to type III radio bursts and jets, respectively. The association rates are independent of flare energies. About 38\% of CFs are related to mini-filament eruptions, and the association rates increase with flare classes. Only 28\% of CFs are related to CMEs, meaning that a majority of them are confined rather than eruptive events. There is a positive correlation between the CME speed and peak SXR flux in 1$-$8 {\AA}, and faster CMEs tend to be wider.

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arXiv2020

The Lyman-alpha Emission in Solar Flares. I. a Statistical Study on Its Relationship with the 1--8 \AA\ Soft X-ray Emission

We statistically study the relationship between the Lyman-alpha (\lya) and 1--8 \AA\ soft X-ray (SXR) emissions from 658 M- and X-class solar flares observed by the {\em Geostationary Operational Environmental Satellite} during 2006--2016. Based on the peak times of the two waveband emissions, we divide the flares into three types. Type I (III) has an earlier (a later) peak time in the \lya\ emission than that in the SXR emission, while type II has nearly a same peak time (within the time resolution of 10 s) between the \lya\ and SXR emissions. In these 658 flares, we find that there are 505 (76.8\%) type I flares, 10 (1.5\%) type II flares, and 143 (21.7\%) type III flares, and that the three types appear to have no dependence on the flare duration, flare location, or solar cycle. Besides the main peak, the \lya\ emission of the three type flares also shows sub-peaks which can appear in the impulsive or gradual phase of the flare. It is found that the main-peak (for type I) and sub-peak (for type III) emissions of \lya\ that appear in the impulsive phase follow the Neupert effect in general. This indicates that such \lya\ emissions are related to the nonthermal electron beam heating. While the main-peak (for type III) and sub-peak (for type I) emissions of \lya\ that appear in the gradual phase are supposed to be primarily contributed by the thermal plasma that cools down.

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