Granule Tracking Research Articles

Photospheric Magnetic Activities Responsible for Soft X‐Ray Pointlike Microflares. I. Identifications of Associated Photospheric/Chromospheric Activities

By combining Yohkoh soft X-ray images with high-resolution magnetograms simultaneously obtained at La Palma, we studied photospheric magnetic signatures responsible for soft X-ray microflares (active-region transient brightenings). In order to have a reliable correspondence between the photosphere and the corona, we studied 16 pointlike transient brightenings with X-ray source size less than 10'' occurring during periods when the seeing was excellent at La Palma, although a lot of transient brightenings were in forms of multiple- or single-loop structures. In half of the studied events, small-scale emergences of magnetic flux loops are found in the vicinity of the transient brightenings. Six events of that half show that a small-scale flux emergence accompanies the X-ray brightening 5-30 minutes prior to its onset. In the other half of the studied events, no apparent evolutionary change of magnetic flux elements is found associated with the transient brightenings. Many of these events are found in rather strong magnetic fields, such as sunspots and pores, implying that small-scale changes of magnetic flux are obscured or suppressed by strong magnetic fields. The horizontal plasma flows derived from local cross-correlation tracking of granules in continuum images are suppressed at the feet of some X-ray transient brightenings.

Performance analysis for T.H.E.M.I.S* image stabilizer optical system. I. (*)Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités de l'atmosphère Solaire

This paper describes the performance of the optical image stabilizer system developed for the franco-Italian T.H.E.M.I.S. telescope, which is currently being built on the Canary Island Tenerife. T.H.E.M.I.S will be one of the largest solar telescopes, and will be the first to be manufactured with a real time tip-tilt correction system integrated into its optical train. A new method is described here for measuring image motions. This method is called granulation tracking. It is based on Fourier transform analysis. A servo-loop model is also proposed, based on experimental measurements and the known time properties of atmospheric turbulence, to deduce the image quality obtained after correction. Method sensitivity and accuracy under various terrestrial turbulence conditions are discussed.

PHOTOSPHERIC AND CORONAL MAGNETIC FIELDS

Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.