Spectral study of activ region site with Ellerman bomb and Hα-ejections. Chromosphere. Arch filament system
1Pasechnik, MN 1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine |
Kinemat. fiz. nebesnyh tel (Online) 2024, 40(5):40-72 |
Language: Ukrainian |
Abstract: The results of the spectral observation analysis in the line of a site of active region NOAA 11024, which was in the main phase of development — its activity increased sharply, are presented. The studied site (its length was 10 Mm) was located in the area of a new serpentine magnetic flow emergence. On it a arch filament system (AFS) was formed, under which the Ellerman bomb (EB) emerged and developed, and a pore formed at a distance of about 7.2 Mm from EB. We study the AFS evolution and investigate the formation and development of all Hα-ejections that formed in its magnetic loops during our observations. Spectral data with a high spatial (~1") and temporal (about 3 s) resolution were obtained with Franch-Italian solar telescope THEMIS (Tenerife, Spain) on July 4, 2009. The observation time was 20 minutes (to 9h52m — 10h11m UT). We used the spectral region that containing the central part of the Hα chromospheric line. In all spectra, Hα-ejections (surges) were visible in the absorption both in the long-wavelength and in the short-wavelength wing of the line. Changes of the Stokes I profiles shape were studied — they were very diverse and significantly different from the profile for the undisturbed chromosphere. Depending on whether the ejection moved to the upward or to the downward, the component of the profile corresponding to it was projected onto the blue or red Hα line wing. Towards the end of the observations, significantly broadened and dual-lobed profiles appeared, indicating that both downward and upward plasma flows existed nearby. It was found that surges can consist of several jets that were formed during successive and periodic magnetic reconnections. Doppler shifts of the profile components were used to calculate the line-of-sight velocities (Vlos) of chromospheric matter in surges. The changes Vlos along the cross-section of the surge jets at the place of their maximum intensity were analyzed. The Vlos of jets were different and probably depended on the magnetic field structure in the surge and the surrounding environment. The direction of jet movement was also different — it depended on the phase of surge development. Most of the Vlos change curves consisted of several segments. This indicates that the large jets were composed of several smaller jets, i.e. they had a fibrous structure. Ascending and descending surge flows often occurred simultaneously, and coincided in time with the increase in EB brightness. A vortex motion of the plasma was observed in the one of the surges for about 3 min, as evidenced by the inclined dark streaks in the spectra. At the moment of the greatest brightness of the EB, there were 7 surges in the studied AR site, and in three of them the plasma moved downwards with Vlos up to 77 km/s, and in five — it moved upward with a much lower Vlos, up to –35 km/s. During our observations, the maximum upward velocities chromospheric matter in the surges reached –110 km/s, the downward velocities reached 90 km/s. In the upper part of the magnetic loops the plasma velocities varied between –25 km/s and 22 km/s. The Vlos values in the site without active formations did not exceed ±2 km/s. It was also analyzed whether the processes of AFS evolution and EB development phases are related. Our work is based on a detailed study of observational data that was obtained with high spatial and temporal resolution, it allowed us to better understand the dynamics of the evolution of the arch filament system under which the Ellerman bomb emerged and developed, as well as to reveal the features of the formation and development of surges that formed in it magnetic loops. They were probably the result of successive and periodic magnetic reconnections, which were associated with the emergence of a new serpentine magnetic flux and occurred when its loops interacted with the surrounding pre-existing magnetic field AR, or between the magnetic loops of the flux itself. |
Keywords: active region, chromosphere, Hα-ejections, line-of-sight velocities, magnetic reconnection, spectra, Sun |