H i  brightness temperature images for selected velocity ranges. The velocity range covered by each map is given in its upper left corner and the displayed temperatures are a mean over the entire velocity width. The lowest temperature contour is  − 15 K and the contour spacing is 5 K. A constant mean brightness temperature value was subtracted from each image (see text). The stellar location is indicated by a star symbol. The white dashed-line circumference drawn in the middle panel marks the position of the Hi hollow feature described in Sect. 3.3.