Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDetection of polarization neutral points in observations of the combined corona and sky during the 21 August 2017 total solar eclipse
99
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the results of polarimetric observations of the total solar eclipse of 21 August 2017 from Rexburg, Idaho (USA). We use three synchronized DSLR cameras with polarization filters oriented at 0{deg}, 60{deg}, and 120{deg} to provide high-dynamic-range RGB polarization images of the corona and surrounding sky. We measure tangential coronal polarization and vertical sky polarization, both as expected. These observations provide detailed detections of polarization neutral points above and below the eclipsed Sun where the coronal polarization is canceled by the sky polarization. We name these special polarization neutral points after Minnaert and Van de Hulst.
rate research
Read More
We report on a search for short-period intensity variations in the green-line FeXIV 530.3 nm emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt-Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view 0.43 degree x 0.43 degree that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of approx. 2 arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of 3.49 images per second. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some 404 000 pixels in the frequency range 0.5-1.6 Hz (periods: 2 second to 0.6 second). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.
In order to study the solar corona during eclipses, a new telescope was constructed. Three coronal images were obtained simultaneously from one objective of the telescope as the coronal radiation passed through three polarisers (whose transmission directions were turned through 0^{circ}, 60^{circ}, and 120^{circ} to the chosen direction); one image without polariser was also obtained. The telescope was used to observe the solar corona during the eclipse of 1 August 2008. We obtained distributions of the polarisation brightness, K-corona brightness, degree of the K-corona polarisation and total polarisation degree; polarisation direction depending on the latitude and radius in the plane of the sky was also obtained. We calculated radial distributions of electron density, depending on the latitude. Properties of all these distributions in different coronal structures were compared. We determined temperature of coronal plasma in different coronal structures on the assumption that there is a hydrostatic equilibrium.
We present an investigation of a coronal cavity observed above the western limb in the coronal red line Fe X 6374 {AA} using a telescope of Peking University and in the green line Fe XIV 5303 {AA} using a telescope of Yunnan Observatories, Chinese Academy of Sciences during the total solar eclipse on 2017 August 21. A series of magnetic field models are constructed based on the magnetograms taken by the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO) one week before the eclipse. The model field lines are then compared with coronal structures seen in images taken by the Atmospheric Imaging Assembly on board SDO and in our coronal red line images. The best-fit model consists of a flux rope with a twist angle of 3.1$pi$, which is consistent with the most probable value of the total twist angle of interplanetary flux ropes observed at 1 AU. Linear polarization of the Fe XIII 10747 {AA} line calculated from this model shows a lagomorphic signature that is also observed by the Coronal Multichannel Polarimeter of the High Altitude Observatory. We also find a ring-shaped structure in the line-of-sight velocity of Fe XIII 10747 {AA}, which implies hot plasma flows along a helical magnetic field structure, in the cavity. These results suggest that the magnetic structure of the cavity is a highly twisted flux rope, which may erupt eventually. The temperature structure of the cavity has also been investigated using the intensity ratio of Fe XIII 10747 {AA} and Fe X 6374 {AA}.
On August 21, 2017, the Airborne Infrared Spectrometer (AIR-Spec) observed the total solar eclipse at an altitude of 14 km from aboard the NSF/NCAR Gulfstream V research aircraft. The instrument successfully observed the five coronal emission lines that it was designed to measure: Si X 1.431 $mu$m, S XI 1.921 $mu$m, Fe IX 2.853 $mu$m, Mg VIII 3.028 $mu$m, and Si IX 3.935 $mu$m. Characterizing these magnetically sensitive emission lines is an important first step in designing future instruments to monitor the coronal magnetic field, which drives space weather events as well as coronal heating, structure, and dynamics. The AIR-Spec instrument includes an image stabilization system, feed telescope, grating spectrometer, and slit-jaw imager. This paper details the instrument design, optical alignment method, image processing, and data calibration approach. The eclipse observations are described and the available data are summarized.
Total eclipses permit a deep analysis of both the inner and the outer parts of the corona using the continuum White-Light (W-L) radiations from electrons (K-corona), the superposed spectrum of forbidden emission lines from ions (E-corona) and the dust component with F-lines (F-corona). By sufficiently dispersing the W-L spectrum, the Fraunhofer (F) spectrum of the dust component of the corona appears and the continuum Thomson radiation can be evaluated. The superposed emission lines of ions with different degrees of ionization are studied to allow the measurement of temperatures, non-thermal velocities, Doppler shifts and abundances. We describe a slit spectroscopic experiment of high spectral resolution for providing an analysis of the most typical parts of the quasi-minimum type corona observed during the total solar eclipse of Aug. 21, 2017 observed from Idaho, USA. Streamers, active region enhancements and polar coronal holes (CHs) are well measured using deep spectra. 60 spectra are obtained during the totality with a long slit, covering +/-3 solar radii in the range of 510 to 590nm. The K+F continuum corona is well exposed up to 2 solar radius. The F-corona can be measured even at the solar limb. New weak emission lines were discovered or confirmed. The rarely observed high FIP ArX line is recorded almost everywhere; the FeXIV and NiXIII lines are well recorded everywhere. For the first time hot lines are also measured inside the CH regions. The radial variations of the non-thermal turbulent velocities of the lines do not show a great departure from the average values. No significantly large Doppler shifts are seen anywhere in the inner and the middle corona. The wings of the FeXIV line show some non-Gaussianity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
