Possibilities of velocity field analysis from Hinode SOT/SP data

Abstract The possibility of analyzing the line of sight (LOS) velocity and its gradient at each point of the Hinode SOT/SP maps using bisector analysis is revealed. A technique for obtaining such gradient is described. To estimate the velocity gradient, it is necessary to know both the velocity value and the layer height to which the bisector point is responded. We have constructed and tested a method to determine this height. We found velocities at the same heights for lines Fe I λ 6301, 6302 Å averaged over the whole map. It turned out that these velocities have some difference that changes with height and time. The error in the estimating of average velocity for the whole map is 2 m·s−1. It follows that the wavelengths of lines 6301 and 6302 given in the NIST tables may differ from the real ones at 5.5 mÅ. Or there is an inaccuracy in the spectrograph dispersion specified in the FITS files. As an example, the curves of changes with the height of the LOS velocity and its gradient were constructed both for points of the whole map and for subsets of the hottest and coldest points.