Solar Physics最新文献

We present results of a dual eclipse expedition to observe the solar corona from two sites during the annular solar eclipse of 14 October 2023 using a novel coronagraph designed to be accessible for amateurs and students to build and deploy. The coronagraph (CATEcor) builds on the standardized eclipse observing equipment developed for the Citizen CATE 2024 experiment. The observing sites were selected for likelihood of clear observations, for historic relevance (near the Climax site in the Colorado Rocky Mountains), and for centrality to the annular eclipse path (atop Sandia Peak above Albuquerque, New Mexico). The novel portion of CATEcor is an external occulter assembly that slips over the front of a conventional dioptric telescope, forming a shaded-truss externally occulted coronagraph. CATEcor is specifically designed to be easily constructed in a garage or “makerspace” environment. We successfully observed some bright features in the solar corona to an altitude of approximately 2.25 R_⊙ during the annular phases of the eclipse. Future improvements to the design, in progress now, will reduce both stray light and image artifacts; our objective is to develop a design that can be operated successfully by amateur astronomers at sufficient altitude even without the darkened skies of a partial or annular eclipse.

We present the design of a portable coronagraph, CATEcor (where CATE stands for Continental-America Telescope Eclipse), that incorporates a novel “shaded-truss” style of external occultation and serves as a proof-of-concept for that family of coronagraphs. The shaded-truss design style has the potential for broad application in various scientific settings. We conceived CATEcor itself as a simple instrument to observe the corona during the darker skies available during a partial solar eclipse, or for students or interested amateurs to detect the corona under ideal noneclipsed conditions. CATEcor is therefore optimized for simplicity and accessibility to the public. It is implemented using an existing dioptric telescope and an adapter rig that mounts in front of the objective lens, restricting the telescope aperture and providing external occultation. The adapter rig, including occulter, is fabricated using fusion deposition modeling (FDM; colloquially “3D printing”), greatly reducing cost. The structure is designed to be integrated with moderate care and may be replicated in a university or amateur setting. While CATEcor is a simple demonstration unit, the design concept, process, and trades are useful for other more sophisticated coronagraphs in the same general family, which might operate under normal daytime skies outside the annular-eclipse conditions used for CATEcor.

A recent discussion (Yelagandula, 2023) of waves in a magnetic flux tube questions the use of the normal velocity continuity condition in the derivation of the standard dispersion relation. We re-assert this condition here.

A point-spread function describes the optics of an imaging system and can be used to correct collected images for instrumental effects. The state of the art for deconvolving images with the point-spread function is the Richardson–Lucy algorithm; however, despite its high fidelity, it is slow and cannot account for light scattered out of the field of view of the detector. We reinstate the Basic Iterative Deconvolution (BID) algorithm, a deconvolution algorithm that considers photons scattered out of the field of view of the detector, and extend it for image subregion deconvolutions. Its runtime is 1.8 to 7.1 faster than the Richardson–Lucy algorithm for (4096 times 4096) pixel images and up to an additional factor of 150 for subregions of (250 times 250) pixels. We test the extended BID algorithm for solar images taken by the Atmospheric Imaging Assembly (AIA), and find that the reconstructed intensities between BID and the Richardson–Lucy algorithm agree within 1%.

In this study, we compile a catalog of metric type II radio bursts using the Radio Solar Telescope Network (RSTN) to study the occurrence, associations, and properties of the emission and their parent solar activity phenomena. According to the intensity and clarity of the radio emission features, we have divided the m-type II radio bursts into two qualitative categories, namely certain and uncertain. We analyzed RSTN data in Solar Cycle 24 (2009 – 2019), which is freely available from four worldwide stations: Learmonth, Sanvito, Sagamore Hills, and Palehua. Through careful visual inspection, we have collected all metric type II bursts detected in the range of 25 – 180 MHz. The relationships between these bursts and solar eruptive events, such as solar flares and coronal mass ejections (CMEs), are studied, and the results are presented and discussed. The outcomes could be used to reveal the occurrence of solar and space-weather activities based on the ground-based radio perspective. The newly assembled catalog of metric type II and associated solar events will be made freely available to the solar scientific community.

Oscillations are ubiquitous in sunspots and the associated higher atmospheres. However, it is still unclear whether these oscillations are driven by the external acoustic waves (p-modes) or generated by the internal magnetoconvection. To obtain clues about the driving source of umbral waves in sunspots, we analyzed the spiral wave patterns (SWPs) in two sunspots registered by IRIS MgII 2796 Å slit-jaw images. By tracking the motion of the SWPs, we found for the first time that two one-armed SWPs coexist in the umbra, and they can rotate either in the same or opposite directions. Furthermore, by analyzing the spatial distribution of the oscillation centers of the one-armed SWPs within the umbra (the oscillation center is defined as the location where the SWP first appears), we found that the chromospheric umbral waves repeatedly originate from the regions with high oscillation power and most of the umbral waves occur in the dark nuclei and strong magnetic field regions of the umbra. Our study results indicate that the chromospheric umbral waves are likely excited by the p-mode oscillations.

Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (X- and M-class flares). Here, we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the Advanced Space-based Solar Observatory and the Chinese H(alpha ) Solar Explorer (CHASE). This flare exhibits an increase of ≈ 6.4% in the photospheric Fe i line at 6569.2 Å and ≈ 3.2% in the nearby continuum. The continuum at 3600 Å also shows an enhancement of ≈ 4.7%. The white-light bright 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 bright kernels, the Fe i line displays an absorption profile that has a good Gaussian shape, with a redshift up to ≈ 1.7 km s⁻¹, while the H(alpha ) line shows an emission profile 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 in the 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.

Type-II radio bursts are believed to occur as a result of the shock driven by flares or coronal mass ejections (CMEs). While the shock waves are important for the acceleration of electrons necessary for the generation of the radio emission, the exact nature of the shock and coronal conditions necessary to produce type-II radio emission is still under debate. In this investigation, we probe the relationship of kinematic characteristics of the type-II radio bursts with the magnetic-field complexity (M_j) of the active regions visible on the photosphere. Our investigation of 64 type-II solar radio bursts, which are associated with flares and CMEs, reveals that M_j is linearly correlated in the logarithmic scale with the starting frequency (f_s) and drift-rate (({Delta f/Delta t})) of type-II radio burst. Further, M_j exhibits a linear correlation with the shock height (r) and electron density ((n_{rm e})) in logarithmic scale. This indicates that high frequency (f_s (geq 100) ({rm MH_{z}})) bursts, which occur at the reconnection site near the solar surface, are produced from a strong magnetically complex region. Further, strong and complex magnetic-field regions produce shocks of higher speeds. Based on the derived plasma parameters of the radio bursts and their relationship with f_s as well as with M_j, we propose that the high-frequency type-II bursts were generated in a special situation when the shock is produced due to magnetic reconnection occurring in the low-lying coronal loops. We conclude that type-II radio bursts can occur even in the inner corona as well as in the outer corona; however, it depends on the magnetic complexity of the active region in which the event occurs.

We present an automated solar flare detection software tool to automatically process solar observed images, detect and track solar flares, and finally compile an event catalog. It can identify and track flares that happen simultaneously or temporally close together. The method to identify a flare is based on the local intensity changes in macropixels. The basic characteristics, such as the time and location information of a flare, are determined with a triple-threshold scheme, with the first threshold (global threshold) to determine the occurrence (location) of the flare and the second and third thresholds (local thresholds) to determine the real start and end times of the flare. We have applied this tool to one month of continuous solar ultraviolet (UV) images obtained by the Solar Disk Imager (SDI) onboard the Advanced Space-based Solar Observatory (ASO-S), which show active phenomena such as flares, filaments or prominences, and solar jets. Our automated tool efficiently detected a total number of 226 solar events. After a visual inspection, we found that only one event was misidentified (unrelated to an active event). We compared the detected events with the GOES X-ray flare list and found that our tool can detect 81% of GOES M-class and above flares (29 out of 36), from which we conclude that the intensity increase in SDI UV images can be considered as a good indicator of a solar flare.

It was shown recently that the model of a semicircular magnetic slab with oblique wave propagation and finite plasma-(beta ) supports two fast surface modes, one of which produces vertical and the other horizontal kink-like motions. Their phase speeds (frequencies) depend upon the internal plasma-(beta ) and slab aspect ratio. Thus the theory predicts the coexistence of two kink modes with different polarizations and periods in a single oscillating loop. In the present work, we aim to perform some analytical extensions of the developed theory and propose methods for seismological estimation of internal plasma-(beta ) and internal Alfvén speed on the bases of multiperiodic kink oscillations of coronal loops. We show that when two fundamental modes of vertically and horizontally polarized kink oscillations with different periods are observed in a single coronal loop, this provides the seismological estimation of the internal plasma-(beta ) and Alfvén speed. We also show that the combined effect of a finite plasma-(beta ) and a slab curvature modifies the ratio of periods (P_{1}/2P_{2}) of the fundamental mode and first overtone of a certain kink oscillation and the internal plasma-(beta ) can be estimated using detected (P_{1}/2P_{2}). We also suggest that the strands with different temperatures that constitute the multithermal loops should oscillate with different periods and this may provide an estimate to the internal Alfvén speed in such loops. These findings are applied to a number of observations of multiperiodic coronal loop kink oscillations. Furthermore, a number of unusual observational results and the results of numerical simulations of kink oscillations in curved magnetic loops were interpreted on the bases of the developed theory.