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Thermal structure of a hot non-flaring corona from Hinode/EIS
摘要： Aims. In previous studies, a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This diagnostic from extreme ultraviolet (EUV) imaging data has also been supported by the matching morphology of emission in the hot Ca XVII line, as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. This evidence is debated because of the unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one such region using EUV spectroscopic data. Methods. In an active region observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we select a sub-region with a very hot plasma component and another cooler sub-region for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis that probe the 5.5 < log T < 7 temperature range uniformly. From these lines, the emission measure distributions are reconstructed with the Markov-chain Monte Carlo method. Results are cross-checked in comparison with the two sub-regions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with narrow, and broadband imagers. Results. We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T ≥ 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result. Conclusions. This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6.
关键词： techniques: imaging spectroscopy,Sun: UV radiation,Sun: corona,techniques: spectroscopic,Sun: X-rays, gamma rays
更新于2025-09-23 15:23:52
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Blobs in recurring extreme-ultraviolet jets
摘要： Context. Coronal jets are one type of ubiquitous small-scale activity that is caused by magnetic reconnection in the solar corona. They are often associated with cool surges in the chromosphere. Aims. In this paper, we report our discovery of blobs in the recurrent and homologous jets that occurred at the western edge of the NOAA active region 11259 on 2011 July 22. Methods. The jets were observed in the seven extreme-ultraviolet (EUV) ?lters of the Atmospheric Imaging Assembly instrument aboard the Solar Dynamics Observatory. Using the base-di?erence images of the six ?lters (94, 131, 171, 211, 193, and 335 ?), we carried out the di?erential emission measure (DEM) analyses to explore the thermodynamic evolutions of the jets. The jets were accompanied by cool surges observed in the Hα line center of the ground-based telescope in the Big Bear Solar Observatory. Results. The jets that had lifetimes of 20?30 min recurred at the same place for three times with an interval of 40?45 min. Interestingly, each of the jets intermittently experienced several upward eruptions at the speed of 120?450 km s?1. After reaching the maximum heights, they returned back to the solar surface, showing near-parabolic trajectories. The falling phases were more evident in the low-T ?lters than in the high-T ?lters, indicating that the jets experienced cooling after the onset of eruptions. We identi?ed bright and compact blobs in the jets during their rising phases. The simultaneous presence of blobs in all the EUV ?lters were consistent with the broad ranges of the DEM pro?les of the blobs (5.5 ≤ log T ≤ 7.5), indicating their multi-thermal nature. The median temperatures of the blobs were ～2.3 MK. The blobs that were ～3 Mm in diameter had lifetimes of 24?60 s. Conclusions. To our knowledge, this is the ?rst report of blobs in coronal jets. We propose that these blobs are plasmoids created by the magnetic reconnection as a result of tearing-mode instability and are ejected out along the jets.
关键词： Sun: chromosphere,Sun: corona,Sun: activity
更新于2025-09-23 15:23:52
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Determination of Differential Emission Measure from Solar Extreme Ultraviolet Images
摘要： The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) has been providing high-cadence, high-resolution, full-disk UV-visible/extreme ultraviolet (EUV) images since 2010, with the best time coverage among all the solar missions. A number of codes have been developed to extract plasma differential emission measures (DEMs) from AIA images. Although widely used, they cannot effectively constrain the DEM at ?aring temperatures with AIA data alone. This often results in much higher X-ray ?uxes than observed. One way to solve the problem is by adding more constraint from other data sets (such as soft X-ray images and ?uxes). However, the spatial information of plasma DEMs are lost in many cases. In this Letter, we present a different approach to constrain the DEMs. We tested the sparse inversion code and show that the default settings reproduce X-ray ?uxes that could be too high. Based on the tests with both simulated and observed AIA data, we provided recommended settings of basis functions and tolerances. The new DEM solutions derived from AIA images alone are much more consistent with (thermal) X-ray observations, and provide valuable information by mapping the thermal plasma from ～0.3 to ～30 MK. Such improvement is a key step in understanding the nature of individual X-ray sources, and particularly important for studies of ?are initiation.
关键词： magnetic reconnection,methods: data analysis,Sun: X-rays, gamma rays,Sun: ?ares,Sun: corona,Sun: UV radiation
更新于2025-09-23 15:23:52
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Magnetic Loops above a Small Flux-emerging Region Observed by <i>IRIS</i> , <i>Hinode</i> , and <i>SDO</i>
摘要： I report on observations of a set of magnetic loops above a region with late-phase ?ux emergence taken by IRIS, Hinode, and SDO. The loop system consists of many transition-region loop threads that are 5″–12″ in length and ～0 5 in width and coronal loops with similar length and ～2″ width. Although the loop system consists of threads with different temperatures, most individual loop threads have temperatures in a narrow range. In the middle of the loop system, there is a clear systematic blueshift of about 10 km s?1 in the transition region that is consistent with a ?ux-emerging picture, while a redshift of about 10 km s?1 in the corona is observed. The nonthermal velocity of the loop system is smaller than that of the surrounding region in the transition region but is comparable that in the corona. The electron densities of the coronal counterpart of the loop system range from 1×109 cm?3 to 4×109 cm?3. The electron density of a transition-region loop is also measured and found to be about 5×1010 cm?3, a magnitude larger than that in the coronal loops. In agreement with imaging data, the temperature pro?les derived from the differential emission measurement technique con?rm that some of the loops have been heated to corona level. Our observations indicate that the ?ux emergence in its late phase is much different from that at the early stage. While the observed transition region is dominated by emerging ?ux, these emerging loops could be heated to corona level, and the heating (if via nonthermal processes) most likely takes place only after they reach the transition region or lower corona.
关键词： Sun: atmosphere,Sun: transition region,Sun: corona
更新于2025-09-23 15:22:29
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Corona assisted gallium oxide nanowire growth on silicon carbide
摘要： This article reports on the use of corona discharge to assist the vapor liquid solid growth of gallium oxide nanowires on silicon carbide substrates. The corona discharge increases the nucleation efficiency of the gold catalysts from 60 % to 98 % for 3C-SiC(111)/Si(111) Si-face substrates and from 15 % to 80 % for 6H-SiC(0001) substrates. The growth mode and crystal structure are not affected by the corona discharge. The gallium oxide growth starts with the formation of [-311] oriented laterally overgrown terrace like nucleation zones with the gold catalyst particles floating on top. With evolving process time, the growth proceeds in the faster [010] direction, resulting in nanowires with an inclination angle of 51° towards the substrate surface. On silicon and sapphire substrates, the nucleation and growth of gallium oxide nanowires are suppressed.
关键词： B2. Silicon carbide,B1. Gallium oxide,A1. Nanowire,A1. Corona discharge,A3. Vapor liquid solid,A3. Vapor phase epitaxy
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Features of Space Charge Relaxation in a Polyimide Printed Circuit Board
摘要： Polyimide films are widely used as substrates for printed circuit boards. The process of space charge accumulating in dielectric substrates is not highly desirable, since space charge distorted the parameters of the electrical circuits. This work is devoted to the study of the accumulation and relaxation of charge in films of thermoplastic polyimide R-BAPB with different degrees of crystallinity, in order to reduce the accumulated charge and the time of its relaxation. Relaxation mechanisms are analyzed and methods for reducing the relaxation time of the space charge are determined.
关键词： PCB,conductivity,electret,homocharge,relaxation,corona discharge,space charge,crystallinity,polyimide
更新于2025-09-23 15:22:29
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The Effect of Environmental Temperature on Negative Corona Discharge Under the Action of Photoionization
摘要： The properties of corona discharge in practical applications are strongly influenced by the variation of environmental parameters. A 2-D axisymmetric hydrodynamic drift–diffusion model coupled with Poisson’s equation and three Helmholtz differential equations is established to investigate the effect of environmental temperature on negative corona discharge under the action of photoionization. This numerical model is performed by a traditional needle-to-plane configuration in dry air at atmospheric pressure. The characteristics of Trichel pulses, negative ion density, electric field, and electron density are discussed in this paper. It is found that the magnitude of Trichel pulses, first pulse duration, and pulse frequency increase with increasing the ambient temperature. Moreover, the effect of photoionization under these conditions is also investigated by simulations intensively.
关键词： negative corona discharge,Trichel pulses,Environmental temperature,photoionization
更新于2025-09-23 15:22:29
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The properties of solar radio spikes with harmonics and the associated EUV brightenings
摘要： Solar radio spikes are narrowband, short duration radio bursts. They are excited by the energetic electrons accelerated during small scale magnetic reconnections. Spikes play an important role in diagnosing magnetic reconnections and studying electron accelerations. In this paper, the solar radio spikes observed by the Chashan Solar Observatory (CSO) spectrograph combined with observations from the Solar Dynamics Observatory (SDO) are used to study the properties of spikes with harmonics. The CSO data show that the central frequency ratio of the third to the second harmonic is 1.35 ± 0.01 and the third harmonic has a larger absolute and relative bandwidth, but a shorter duration than the second one. By studying the correlation between light curves of the solar radio spike and those of bright points at different Extreme UltraViolet (EUV) passbands, the best associated EUV bright point and passbands are determined. The spike source properties are discussed based on the extrapolated magnetic field around the associated EUV bright point.
关键词： Radio emission, active regions,Radio bursts, meter-wavelengths and longer, spikes,Magnetic fields, corona
更新于2025-09-23 15:22:29
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Response of Hinode XRT to quiet Sun, active region and flare plasma
摘要： Aims. We examine the response of the Hinode X-Ray Telescope (XRT), using simultaneous observations with the Hinode Extreme-ultraviolet Imaging Spectrometer (EIS), for a flare, an active region and a quiet Sun region. We also examine the relative intensity calibration of EIS and XRT. Methods. EIS differential emission measure distribution (DEM) curves were used to create synthetic spectra with the CHIANTI atomic database. The contribution of spectral lines and continuum emission to each of the XRT channels was determined from the synthetic spectra, which were then convolved with the effective area of each XRT channel. The predicted total count rates for each channel were compared with the observed count rates. The effects of varying elemental abundances and the temperature range for the inversion were investigated. DEMs obtained from the XRT bands were also computed and compared to those obtained with EIS. Results. For the active region observations, the observed XRT count rates for most of the channels are in reasonable agreement with those predicted using EIS observations, but are dependent on the elemental abundances chosen. Significant discrepancies between predicted and observed count rates were found and are discussed for the adjacent quiet Sun region and also for the flare. Synthetic spectra and continuum emission contributing to the XRT channels are presented and discussed for the active region, quiet Sun and flare observations.
关键词： Sun: abundances,gamma rays,Sun: corona,Sun: X-rays
更新于2025-09-23 15:22:29
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Characterization of the White-light Brightness of the F-corona between 5° and 24° Elongation
摘要： The white-light F-corona arises from light scattered by circumsolar dust. Using weekly models of the eastern side of the F-corona between 5° and 24° elongation, we analyzed the elongation and time dependence of the brightness of its photometric axis. The models were constructed from STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We found that the brightness profiles can be approximated by power laws, with the coefficients of the models depending upon the observer’s ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes of the dust plane, nor is the behavior similar in the two halves of the spacecraft orbit delimited by the line of nodes. The exponents range between ?2.31 and ?2.35, the former occurring when the observer is at the nodes. The asymmetry observed in the behavior of the proportionality constant is indicative of the projected center of the dust cloud being offset from the Sun’s center by ～0.4 Re. The coefficients exhibit a secular variation correlated with the location of the barycenter of the solar system. We also used the HI-1 frames obtained during STEREO-A calibration rolls to model the 360° F-corona. We found that (1) its flattening index (f = 1 - Rpol/Req) decreases from ～0.66 to ～0.46 with decreasing elongation and (2) the isophotes’ shape can be approximated by a series of superellipses, with the superellipse index n increasing (nonlinearly) with brightness (n ~ 1.65). Cubic extrapolation of the results below 5° elongation points to a circular F-corona below ～1° elongation.
关键词： scattering,zodiacal dust,methods: data analysis,Sun: corona,techniques: image processing
更新于2025-09-23 15:22:29