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To understand the physical mechanisms for activity and heating in the solar atmosphere, the magnetic coupling from the photosphere to the corona is an important piece of information from the Hinode observations, and therefore precise positional alignment is required among the data acquired by different telescopes. The Hinode spacecraft and its onbo...
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... Before the solar image is released, it needs to go through a lot of processes and corrections. Among them, image positioning is an extremely important step [11][12][13]. Finding the accurate center and radii is not a trivial problem for solar EUV images since the corona is complex. For solar images in visible and infrared bands, the boundary can be calculated using solar limb darkening [14][15][16]. ...
An algorithm to extract the disk boundary and center of EUV solar image using the Sobel operator, Fuzzy Local Information C-Means Clustering algorithm (FLICM), and the least square circle fitting method is proposed in this paper. The Sobel operator can determine the solar disk boundary preliminarily, and then the image is processed further using the FLICM algorithm. After the background is removed based on the clustered image and the boundary points can be highlighted, these points are fitted using the least square circle fitting method as the final boundary circle. The solar data used in this paper was from the observation of the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) instrument. The 2523 19.3 nm solar images covering solar minimum, moderate solar activity, and more active suns were calculated using the proposed algorithm to analyze the accuracy statistically. The statistical comparison results demonstrate that the method is accurate and effective. This method can support the processing of solar EUV images and serve the operational system of a space weather forecast.
... The X-Ray Telescope (XRT; Golub et al. 2007;Kano et al. 2008) on the Hinode satellite (Kosugi et al. 2007) repeatedly and continuously acquired Al-poly filter images every 4 s with occasional exposures of G-band images (XOB #1B76). The image size is 128 × 128 pixels, with a pixel scale of 1 031 (Shimizu et al. 2007). The standard calibration routine on Solar SoftWare was used to calibrate the time series of the XRT images. ...
Microflares have been considered to be among the major energy input sources to form active solar corona. To investigate the response of the low atmosphere to events, we conducted an Atacama Large Millimeter/submillimeter Array (ALMA) observation at 3 mm, coordinated with Interface Region Imaging Spectrograph (IRIS) and Hinode observations, on 2017 March 19. During the observations, a soft X-ray loop-type microflare (active region transient brightening) was captured using the Hinode X-ray telescope in high temporal cadence. A brightening loop footpoint is located within narrow fields of view of ALMA, IRIS slit-jaw imager, and Hinode spectropolarimeter. Counterparts of the microflare at the footpoint were detected in Si iv and ALMA images, while the counterparts were less apparent in C ii and Mg ii k images. Their impulsive time profiles exhibit the Neupert effect pertaining to soft X-ray intensity evolution. The magnitude of thermal energy measured using ALMA was approximately 100 times smaller than that measured in the corona. These results suggest that impulsive counterparts can be detected in the transition region and upper chromosphere, where the plasma is thermally heated via impinging nonthermal particles. Our energy evaluation indicates a deficit of accelerated particles that impinge the footpoints for a small class of soft X-ray microflares. The footpoint counterparts consist of several brightening kernels, all of which are located in weak (void) magnetic areas formed in patchy distribution of strong magnetic flux at the photospheric level. The kernels provide a conceptual image in which the transient energy release occurs at multiple locations on the sheaths of magnetic flux bundles in the corona.
... We uniformly scale the pixel values of each image so that the ratios of the means of the three images are equal to the ratios of the fluxes of a 5770 K black body at the three filters' central wavelengths. We next correct for small, fixed, filter-dependent variations in translation and pixel scale between images (see Shimizu et al., 2007), as well as any small offsets in pointing that may occur between images. Within each image triplet, we find the translations and scalings that maximize the sum of products of the corresponding pixels for each pair of images. ...
... Within each image triplet, we find the translations and scalings that maximize the sum of products of the corresponding pixels for each pair of images. These values are consistent with those of Shimizu et al. (2007). For our final, aligned images we use the average of the fitted scaling factors across all image triplets (calculated per wavelength pair) in light of the fixed nature of the varying plate scales, but we use directly the best-fit translational factors for each image pair to guard against any slight variations in telescope pointing. ...
Magnetic bright points on the solar photosphere mark the footpoints of kilogauss magnetic flux tubes extending toward the corona. Convective buffeting of these tubes is believed to excite MHD waves, which can propagate to the corona and deposit heat. Measuring wave excitation via bright-point motion can thus constrain coronal and heliospheric models. This has been done extensively with centroid tracking to estimate kink-mode wave excitation. DKIST will be the first telescope to resolve well the shapes and sizes of bright points, which can probe wave modes that have been difficult or impossible to study to date. I develop two complementary ways to take the first step in such an investigation, which I demonstrate on MURaM-simulated images of DKIST-like resolution as a proof-of-concept in preparation for future observations. I show that these additional wave modes may double the energy budget of this wave-heating model. I also investigate the convection driving bright-point motion. I use a simplified model of granulation alongside MURaM to explore how bright-point motion depends on convective properties, and I show the importance of turbulence to high-frequency motion. Separately, I investigate high-frequency, stochastic brightness fluctuations ("flicker" or $F_8$) in Kepler light curves, which are the signature of stellar convection. I confront a physical model of flicker with measured values across the H-R diagram. I improve the model's agreement with observations by including the effect of the Kepler bandpass on measured flicker, including metallicity in determining convective Mach numbers, and using scaling relations from a wider set of numerical simulations. I also explore how future research could improve the model. In doing so, I help to establish flicker as a stellar constraint on convective simulations, which may support future advances in both stellar and solar convection.
... We uniformly scale the pixel values of each image so that the ratios of the means of the three images are equal to the ratios of the fluxes of a 5770 K black body at the three filters' central wavelengths. We next correct for small, fixed, filter-dependent variations in translation and pixel scale between images (see Shimizu et al. 2007), as well as any small offsets in pointing that may occur between images. Within each image triplet, we find the translations and scalings that maximize the sum of products of the corresponding pixels for each pair of images. ...
... Within each image triplet, we find the translations and scalings that maximize the sum of products of the corresponding pixels for each pair of images. These values are consistent with those of Shimizu et al. (2007). For our final, aligned images we use the average of the fitted scaling factors across all image triplets (calculated per wavelength pair) in light of the fixed nature of the varying plate scales, but we use directly the best-fit translational factors for each image pair to guard against any slight variations in telescope pointing. ...
Light curves produced by the Kepler mission demonstrate stochastic brightness fluctuations (or "flicker") of stellar origin which contribute to the noise floor, limiting the sensitivity of exoplanet detection and characterization methods. In stars with surface convection, the primary driver of these variations on short (sub-eight-hour) timescales is believed to be convective granulation. In this work, we improve existing models of this granular flicker amplitude, or $F_8$, by including the effect of the Kepler bandpass on measured flicker, by incorporating metallicity in determining convective Mach numbers, and by using scaling relations from a wider set of numerical simulations. To motivate and validate these changes, we use a recent database of convective flicker measurements in Kepler stars, which allows us to more fully detail the remaining model--prediction error. Our model improvements reduce the typical misprediction of flicker amplitude from a factor of 2.5 to 2. We rule out rotation period and strong magnetic activity as possible explanations for the remaining model error, and we show that binary companions may affect convective flicker. We also introduce an "envelope" model which predicts a range of flicker amplitudes for any one star to account for some of the spread in numerical simulations, and we find that this range covers 78% of observed stars. We note that the solar granular flicker amplitude is lower than most Sun-like stars. This improved model of convective flicker amplitude can better characterize this source of noise in exoplanet studies as well as better inform models and simulations of stellar granulation.
... The roll angles of the X-Ray Telescope (XRT: and the Solar Optical Telescope (SOT: , both on board Hinode, have been determined using transits of Mercury by Shimizu et al. (2007). The temporal evolution of the XRT roll angle was later measured by , who used correlations with AIA and the Helioseismic and Magnetic Imager (HMI: on board SDO. ...
La couche la plus externe de l’atmosphère solaire, la couronne, est composée de plasma dont la température dépasse de plusieurs ordres de grandeur celle de la surface.Expliquer comment la couronne est chauffée à des températures de l’ordre d’un million de degrés constitue un défi majeur de la physique solaire.Dans ce contexte, je m’intéresse au chauffage des boucles coronales (qui sont des structures composées de plasma confiné dans des tubes de champ magnétique) et plus particulièrement aux cycles de non-équilibre thermique (TNE).L’étude de ces cycles permet de caractériser le chauffage des boucles.Ces cycles se développent dans des boucles soumises à un chauffage fortement stratifié, localisé près de leurs pieds.Ils se traduisent notamment par une variation périodique de la température et de la densité du plasma dans la boucle.Ces variations engendrent des pulsations d’intensité de longue période, qui sont détectées depuis peu dans l’émission en extrême-ultraviolet (EUV) de certaines boucles coronales.Par ailleurs, des écoulements périodiques de plasma à températures coronales se produisent durant ces cycles.Dans certains cas, le plasma qui s’écoule peut refroidir de plusieurs ordres de grandeur et former de la pluie coronale périodique.Durant ma thèse, j’ai travaillé à la première détection de ces écoulements à haute et à basse température.En utilisant des séries temporelles de spectres EUV de l’instrument Hinode/EIS, j’ai mesuré la vitesse Doppler du plasma dans des boucles dans lesquelles on détecte des pulsations d’intensité.Cela m’a permis de détecter des écoulements de plasma à température coronale associé à certaines pulsations d’intensité.Par ailleurs, j’ai participé à la détection d’un événement de pluie coronale périodique (à température plus froide) dans des séries d’images de l’instrument SDO/AIA.Ces détections permettent de confirmer que les pulsations d’intensité de longue période sont bien le résultat de cycles de TNE, ainsi que d’apporter de nouvelles contraintes sur le chauffage des boucles coronales.Cela permet notamment de conclure que le chauffage des boucles coronales est localisé près de leurs pieds et que son temps de répétition est inférieur au temps de refroidissement du plasma.Afin de détecter les écoulements à haute température, j’ai dû corriger de nombreux effets instrumentaux de EIS.J’ai notamment développé une nouvelle méthode pour aligner les spectres avec des images de l’instrument AIA, qui permet de corriger l’angle de roulis et la variation aléatoire du pointage de EIS.En appliquant cette méthode à un grand nombre de spectres, j’ai réalisé la première mesure systématique de l’angle de roulis de l’instrument.Par la suite, j’ai réalisé des simulations numériques du cas de pluie coronale périodique.Dans ces simulations, j’ai calculé l’évolution du plasma dans la boucle pour différents paramètres de chauffage et différentes géométries du champ magnétique.Cela m’a permis d’identifier les paramètres de chauffage permettant de reproduire le comportement observé.Avec ces simulations, j’ai par ailleurs pu comprendre comment l’asymétrie de la boucle et du chauffage conditionnent la température minimale atteinte par les écoulements qui se forment lors des cycles de non-équilibre thermique.
... The roll angles of the X-Ray Telescope (XRT: Golub et al., 2007) and the Solar Optical Telescope (SOT: Tsuneta et al., 2008), both on board Hinode, have been determined using transits of Mercury by Shimizu et al. (2007). The temporal evolution of the XRT roll angle was later measured by Yoshimura and McKenzie (2015), who used correlations with AIA and the Helioseismic and Magnetic Imager (HMI: Scherrer et al., 2012) on board SDO. ...
We present a new coalignment method for the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. In addition to the pointing offset and spacecraft jitter, this method determines the roll angle of the instrument, which has never been systematically measured, and which is therefore usually not corrected. The optimal pointing for EIS is computed by maximizing the cross-correlations of the Fe xii 195.119 Å line with images from the 193 Å band of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). By coaligning 3336 rasters with high signal-to-noise ratio, we estimate the rotation angle between EIS and AIA and explore the distribution of its values. We report an average value of \((-0.387 \pm 0.007)^{\circ}\). We also provide a software implementation of this method that can be used to coalign any EIS raster.
... The roll angles of the X-Ray Telescope (XRT: Golub et al., 2007) and the Solar Optical Telescope (SOT: Tsuneta et al., 2008), both on board Hinode, have been determined using transits of Mercury by Shimizu et al. (2007). The temporal evolution of the XRT roll angle was later measured by Yoshimura and McKenzie (2015), who used correlations with AIA and the Helioseismic and Magnetic Imager (HMI: Scherrer et al., 2012) on board SDO. ...
We present a new coalignment method for the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. In addition to the pointing offset and spacecraft jitter, this method determines the roll angle of the instrument, which has never been systematically measured, and is therefore usually not corrected. The optimal pointing for EIS is computed by maximizing the cross-correlations of the Fe XII 195.119 \r{A} line with images from the 193 \r{A} band of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). By coaligning 3336 rasters with high signal-to-noise ratio, we estimate the rotation angle between EIS and AIA and explore the distribution of its values. We report an average value of (-0.387 $\pm$ 0.007)\deg. We also provide a software implementation of this method that can be used to coalign any EIS raster.
... Investigation of daily AIA pointing variations uses observational data of the 5-6 June 2012 Venus transit (23:00:00 UT -04:00:00 UT), while Venus' silhouette was fully visible on the solar disk ( Figure 3). Venus' transit provides the ideal fiducial reference for measuring such errors since its silhouette must be seen at identical locations in each passband when the transit speed across the solar surface is accounted for (Kamio et al., 2010;Shimizu et al., 2007). Daily pointing variations from the various AIA passbands are determined from a direct comparison of the heliographic coordinates of Venus' center to those predicted by deriving the Venus' velocity using running difference images (1700Å passband; see Figure 4). ...
Achieving subarcsecond co-registration across varying time-lines of multi-wavelength and instrument images is difficult and requires an accurate characterization of the instrument pointing jitter. We investigated the internal pointing errors on daily and yearly time-scales that occur across the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI). Using cross-correlation techniques on the AIA 1700 Å passband and the HMI line-of-sight magnetograms from three years of observational image pairs at approximately three-day intervals, internal pointing errors were quantified. Pointing variations of ± 0.26″ (jitter-limited) and ± 0.50″ in the solar East–West (x) and North–South (y) directions, respectively, were measured. AIA observations of the Venus transit in June 2012 were used to measure existing coalignment offsets in all passbands. We found that the AIA passband pointing variations are 〈ΔX
CO〉=1.10″±1.41″ and 〈ΔY
CO〉=1.25″±1.24″ when aligned to the HMI nominal image center, referred to here as the CutOut technique. Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that the image-center positions provided by the instrument teams achieve single-pixel accuracy on time scales shorter than their characterization. However, daily AIA passband pointing variations of ≲ 1.18″ indicate that autonomous subarcsecond co-registration is not fully achieved yet.
... The EIS level-0 data were processed and calibrated via the standard Solar SoftWare (SSW) routine eis prep.pro. Additional corrections were made for coalignment between EIS's short wavelength (171-212Å) and long wavelength (250-290Å) bands (Young and Gallagher, 2008); instrument and orbital jitter variations (Shimizu et al., 2007); the sinusoidal spectrum drift of the lines on the CCD due to orbital changes , and the tilt of the emission lines on the detector. These corrections resulted in an absolute wavelength calibration of ± 4.4 km s −1 (Kamio et al., 2010). ...
Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3 – 6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤ 25 km s−1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤ 20 km s−1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.
... The transit of Venus is a very convenient tool for calibrating SODISM (psf and plate scale); indeed, the transit of a planet has been used in the past to calibrate other solar space telescopes, especially during transits of Mercury (Auchère, DeForest, and Artzner, 2000;Shimizu et al., 2007). To determine the plate scale, it is necessary to know the ephemeris and to calculate the positions of the Sun and Venus (from images taken by the SODISM instrument). ...
Knowledge of the Solar Diameter Imager and Surface Mapper (SODISM) plate scale is a fundamental parameter for obtaining the solar radius. We have determined the plate scale of the telescope on the ground and in flight onboard the Picard spacecraft. The results show significant differences; the main reason is that the conditions of observation are not the same. In addition, the space environment has an impact on the performance of a metrology instrument. Therefore, calibration in space and under the same conditions of observation is crucial. The transit of Venus allowed us to determine the plate scale of the SODISM telescope and hence the absolute value of the solar radius. The transit was observed from space by the Picard spacecraft on 5 - 6 June 2012. We exploited the data recorded by SODISM to determine the plate scale of the instrument, which depends on the characteristics of optical elements (mirrors, filters, or front window). The mean plate scale at 607.1 nm is found to be 1.0643 arcseconds pixel-1 with 3×10-4 RMS. The solar radius at 607.1 nm from 1 AU is found to be equal to 959.86 arcseconds.
