In the upper part of the solar atmosphere with the help of suborbital telescope’s High Resolution Coronal Imager, which makes images with very high resolution were able to detect previously seen parts — a thin filament of hot plasma, forming a coronal loop. Article published in The Astrophysical Journal.
Coronal loops are the basic elements of the corona (upper atmosphere) of the Sun as they are observed in the quiet Sun and increased his level of activity. Their structure examined from 1940-ies, observing in the hard ultraviolet and x-ray ranges. In active regions so far distinguished two kinds of loops — short hot loops in the middle of these areas, usually observed in x-rays, and less hot and longer loops surrounding the centre, which are visible in ultraviolet light. Studying the heating of coronal loops, it is necessary to understand, are they uniform in temperature along the line of sight or not. If such loops is non-uniform on temperature, therefore, they contain even smaller structures or consist of structures that are impossible to resolve. Determination of the presence of such structures is an important step in understanding how plasma is heated to coronal loops.
A group of researchers from the UK, Germany and the United States under the leadership of Robert Walsh (Robert W. Walsh) from the University of Central Lancashire studied the images of active region AR 12712 obtained by suborbital telescope NASA High Resolution Coronal Imager (Hi-C). This telescope was first launched using sounding rocket on 11 July 2012 and received image with a spatial resolution of 0.3-0.4 seconds of arc and an interval between shots of five seconds, allowing to see the crown much more than space telescopes. For example, the solar dynamics Observatory (SDO/AIA) takes pictures with a resolution of 1.5 arc seconds with an interval of 12 seconds, and the Observatory SOHO (Solar and Heliospheric Observatory), with a resolution of five arc seconds and with an interval of 12 minutes. The second launch of the telescope was unsuccessful, the data has not been collected. Therefore, the third flight of Hi-C, which was held on 29 may 2018, called 2.1. Unlike the first flight, during which the pictures were made in the hard ultraviolet radiation with a bandwidth of 19.1 nm in the second flight, the telescope worked in a bandwidth of 17.2 nm. Six minutes was made 78 pictures with exposure for two seconds and the interval is 4.4. seconds and the spatial resolution was even higher — 0,129 seconds of arc. During the flight, the telescope has experienced some problems with orientation in space, which led to periodic vibration, which about half of the pictures turned out clear enough.
Matching images Hi-C 2.1 data observations of the same region telescope SDO/AIA with a bandwidth of 17.1 nanometers, the researchers measured the thickness 49 of the filamentary structures in the solar corona. Pictures of the new telescope revealed the presence in the region with more intense radiation structures with a thickness of about 202 km, while the most usual are distinguishable filaments had a thickness of about 513 km. In area with less intense radiation is dominated by threads with a thickness of 388 km. the Next task is to check whether there were such fine structure in the other passbands and to measure their temperature. If it is confirmed the existence of a wide range of temperatures it will be a good evidence for MultiTerminal models, which solve the problem of heating the corona. However, this requires a space telescope that will work with the same resolution as Hi-C 2.1, astrophysicists believe.
The resolution of solar telescopes, operating in different bands is constantly increasing. So, located in Hawaii DKIST (Daniel K. Inouye Solar Telescope), possessing a four-meter primary mirror and adaptive optics system, recently received the photosphere, which can distinguish objects as small as 30 km.