Yunnan Observatories

Abstract Bipolar light bridges (BLBs) are bright regions located between sunspot umbrae of opposite magnetic polarity. They are typically characterized by strong magnetic fields and intense flows, which are believed to be closely associated with major solar flares. Despite their importance, their fine structure, formation, and evolution remain poorly understood. In this work, we analyze the observations of a well-defined BLB obtained by the Goode Solar Telescope (GST) at the Big Bear Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The high-resolution GST observations reveal that the BLB is composed of fine, penumbral filament-like structures with widths of approximately 100–150 km. The corresponding Doppler velocity maps present a stable pattern of spatially adjacent red- and blueshifted patches within the BLB throughout the 5.5 hr GST observation. HMI observations show that the BLB arises from the converging and shearing motions of sunspots with opposite polarities. Penumbral regions originating from different polarities gradually evolve and interact, eventually forming the BLB. The observed Doppler velocity pattern, characterized by red- and blueshifted patches, can be interpreted as a projection effect of the Evershed flow within the penumbrae. Therefore, we argue that the BLB is formed through the compression and stretching of penumbral structures from oppositely polarized sunspots.

Extremely high-energy SEPs, which attain energies in the GeV range, are accelerated during impulsive solar flares and in association with CMEs. These relativistic particles represent a primary driver of hazardous space weather phenomena. They pose significant risks to spacecraft operations and crew safety during deep-space missions, while also threatening ground-based infrastructure, particularly power grids and other critical components of the electromagnetic environment, through geomagnetic disturbances and induced currents. Spectral observations indicate that the acceleration of SEPs to GeV energies involves highly complex, multi-component processes characterized by diverse ion compositions. The particle population predominantly comprises hydrogen (protons and electrons, approximately 73%), helium (approximately 25%), and heavier ions. Notably, the mass-to-charge ratio (A/Q) differs markedly between helium isotopes: 1.5 for ³He²⁺ and 2.0 for ⁴He²⁺. In the present study, we examine the acceleration processes and ³He enrichment in SEP events within a statistical plasma-physics framework integrated with turbulence theory. Our methodology explicitly accounts for the realistic proton-to-electron mass ratio, the distinct mass-to-charge ratios of relevant ion species, and the effects of turbulence resistivity and viscosity. These elements are incorporated into a fully coupled hydrodynamics–magnetohydrodynamics–kinetic model that bridges continuous spatial and temporal scales, thereby circumventing the traditional separation of micro-kinetic and macro-dynamic regimes. Numerical simulations are conducted on a supercomputer using our newly developed relativistic hybrid particle-in-cell and lattice-Boltzmann method (RHPIC-LBM) code. This advanced computational approach facilitates self-consistent modeling of the multi-scale, multiphase dynamics underlying the extreme ³He enhancements observed in impulsive solar SEP events. The simulations reveal that high-frequency magnetic fluctuations at kinetic scales play a pivotal role in generating self-organized perturbations. Concurrently, plasma velocity fluctuations sustain and amplify these waves through self-feeding mechanisms. When the frequency of these perturbations approaches the Langmuir oscillation frequency, resonant wave–particle interactions become particularly efficient. Langmuir turbulence, driven by nonlinear resonant wave–particle coupling, preferentially accelerates ions whose resonance conditions match those of ³He. This selective resonance renders the acceleration of ³He substantially more efficient than that of ⁴He, thereby providing a compelling explanation for the extreme ³He enrichment characteristic of impulsive SEP events.

Context. The thermally pulsating asymptotic giant branch (TP-AGB) phase plays a key role in the evolution of low- to intermediate-mass stars because it drives the mass loss that influences their final stages and contributes to galactic chemical enrichment. However, the mechanisms behind the mass loss, particularly at the end of the AGB phase, are still not well understood. Aims. We investigated the relationship between the stellar parameters and envelope dynamics during the TP-AGB phase with the aim of evaluating whether dynamical instabilities in the envelope can act as a possible mass-loss mechanism. Methods. We used the hydrodynamics method in MESA to simulate the dynamical pulsations and resulting mass loss during the TP-AGB phase of a star that evolved from a 1.5 M ⊙ zero-age main-sequence. Results. Our simulations reproduced the dynamical pulsation behavior of stars during the TP-AGB phase, demonstrating that the envelope mass is a key factor governing pulsational properties. As the envelope mass decreases, both the pulsation period and radial amplitude increase, as is consistent with observational trends. For the 1.5 M ⊙ model, once the envelope mass declines to approximately 0.25 M ⊙ , the model enters a regime of violent pulsations, potentially ejecting the remaining envelope within a few hundred years. Conclusions. We suggest that the instability can act as the dominant mass-loss mechanism at the end of the TP-AGB phase, marking a rapid transitional stage toward the post-AGB phase.

Abstract The R2Pub, built by Beijing Planetarium, is a state-of-the-art 60 cm equatorial binocular telescope located at the Daocheng Site (with an altitude of 4700 m) of Yunnan Observatories in China. This paper provides an overview of the R2Pub telescope system, discusses its design and capabilities, and presents an evaluation of its performance for astronomical surveys. R2Pub is a prime-focus binocular system, with each tube covering a field of view of about 18 deg 2 . This system is designed to detect various transients in local universe, including variables, eclipsing binaries, supernovae, gamma-ray bursts afterglow, tidal disruption events, Active Galactic Nuclei, and other unknown transients, which are ideal targets for both time-domain astronomy research and science population. The entire R2Pub system has completed the construction and installation of all observatory infrastructure, including the dome, equatorial mount, optical tube, and associated components, and has now entered the commissioning phase. The high-altitude location, good seeing, and dark background sky light at Daocheng site ensure optimal observational conditions for time-domain astronomy. Performance testing during the commissioning phase has demonstrated that the R2Pub system can achieve a 5 σ limiting magnitude of approximately 18.7 mag in the Pan-STARRS r ′ band for 60 s exposures. The ongoing observations from R2Pub is expected to contribute significantly to the study of time-variable phenomena in the universe and greatly improve the public outreach in astronomy. In particular, the binocular telescope systems capable of simultaneous dual-band observations can obtain the instantaneous color information of transient sources, enabling more accurate characterization of their physical properties and evolution, and providing a significant advantage in rapid distinguishing different classes of variables and transients.

The pattern synthesis technique of antenna arrays has a wide range of applications in radar and communication systems, which is an important research direction in the field of smart antennas. In order to improve the optimization performance of pattern synthesis of linear antenna arrays, an optimization method based on the Modified RIME Optimization Algorithm (MRIME) is proposed. RIME is a new heuristic algorithm inspired by the condensation process of frost ice in nature, which has a unique update mechanism with strong convergence as well as randomization. In the present work, MRIME is used for optimal pattern synthesis of a linear antenna array (LAA). One part of the present study is to optimize the side lobe level by optimizing the antenna current amplitude while maintaining a uniform spacing; the other part is to optimize the antenna position while assuming a uniform excitation in the synthesis of a sparse LAA, where constraints are imposed on the spacing of the array elements and aperture length, and suppression of the side lobe level with the position of the zeros in the specified direction is also achieved. In this article, simulation experiments for uniform linear arrays as well as sparse linear arrays are presented in detail, and the results show that the MRIME optimization algorithm outperforms most of the existing evolutionary classes of optimization algorithms in optimizing the side lobe level. This illustrates the potential of utilizing the MRIME optimization algorithm for antenna arrays and various other electromagnetism-related challenges.

We present a multiwavelength study of the symbiotic recurrent nova T Coronae Borealis (T CrB), using the Swift Burst Alert Telescope (BAT)/ X-Ray Telescope (XRT) / UltraViolet Optical Telescope (UVOT) and American Association of Variable Stars Observers (AAVSO) observations from 2005 to 2025. Our analysis spans quiescent, high, and pre-eruption dip states. We find that brightening amplitudes increase toward shorter wavelengths in both the optical and UV bands, while the UV and X-ray fluxes are generally anticorrelated throughout all phases. During the 2023-2024 pre-eruption dip, soft and hard X-rays increased as optical and UV brightness declined, consistent with a transition from an optically thick to an optically thin boundary layer driven by a reduction in the accretion rate. We also report, for the first time, a second, lower-amplitude dip occurring between September 2024 and February 2025 following the primary 2023–2024 pre-eruption dip. The observed variability supports an accretion-variation scenario as a unifying explanation for both the high and dip states and may signal an imminent nova eruption.

Abstract As the 15th paper in a series reporting on a large reverberation mapping (RM) campaign of super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs), we present the results of measurements of the Mg ii lines in 18 SEAMBHs monitored spectroscopically from 2017 to 2024. Among these, the time lags of Mg ii have been successfully determined for eight of the 18 objects, thereby expanding the current Mg ii RM sample, particularly at higher accretion rates. By incorporating measurements of the line widths, we determine the masses of their central supermassive black holes. Based on these new measurements, we update the relation between the Mg ii radius and the monochromatic luminosity at 3000 Å ( R MgII – L 3000 relation), yielding a slope of 0.24 ± 0.03, which is slightly shallower than, yet still consistent with, previously reported values. Similar to the H β lines, the Mg ii time lags in SEAMBHs are shorter than those of AGNs with normal accretion rates at comparable luminosities. The deviation of AGNs from the best-fit R MgII – L 3000 relation shows a strong correlation with the accretion rate, while no significant correlation is found between the deviation and the flux ratio of UV iron to Mg ii .

Prestressed concrete beams are widely used in bridge and building structures, and their performance is directly related to the overall safety and durability. To predict the performance of prestressed concrete beams, machine learning (ML) has been widely applied. However, the selection of model hyperparameters remains a significant challenge in achieving efficient and accurate predictions. To address this issue, this paper investigates the application of Optuna for hyperparameter optimization to four machine learning models: XGBoost, Decision Trees (DT), Random Forests (RF), and LightGBM (LGBM). This study demonstrates that adopting this optimization method significantly improves the efficiency of the prediction process and successfully identifies the optimal hyperparameter combinations for each model. The performance of the final models was validated using a set of performance evaluation metrics. The results show that the LGBM model achieved an R2 value exceeding 0.98 for strength prediction and over 0.8 for crack resistance prediction. Therefore, hyperparameter tuning using Optuna not only significantly improves the prediction accuracy of the models but also effectively reduces computational and time costs.

Abstract We present the results of low-resolution spectroscopic and densely sampled multiband photometric follow-up of supernova (SN) 2024aecx. The SN was discovered in the spiral galaxy NGC 3521 (distance ∼ 11 Mpc) within a day after the explosion. The early spectra of SN 2024aecx show a weak signature of hydrogen lines, which disappeared in ∼30 days after the explosion. Light curves in all bands show a distinct feature of two peaks, and the first peak is likely due to the emission from shock cooling. The early-phase evolution of the light curve of SN 2024aecx is similar to the typical Type IIb events, but the decay rate in different bands (e.g., Δ m 15 = 1.60 ± 0.05 mag, g band) is significantly faster in the postpeak phase. It attained the secondary maximum in ∼19 days ( g band) with a peak absolute magnitude of M g = –17.94 ± 0.10 mag. The colors of SN 2024aecx tend to be redder in early epochs (<8 days), then it grows bluer for a period, then redder again >20 days after explosion. The analytical model fitting to the light curves reveals an envelope mass and progenitor radius in the ranges ∼0.03–0.24 M ⊙ and ∼169–200 R ⊙ , respectively. Modeling of the pseudobolometric light curve suggests that synthesized 56 Ni in the explosion was ∼0.15 M ⊙ with ejecta mass and kinetic energy of ∼0.7 M ⊙ and ∼0.16 × 10 51 erg, respectively. The observational properties and modeling indicate that the progenitor of SN 2024aecx belongs to the category of extended progenitors.