2D spectra of the SE shell of HB9 extracted from the slit shown in Fig. 1. The left and right panels show the spectra taken on March 29 and March 30 2024, respectively. The y axis is the distance in arcmin from the bright star used for slit acquisition (appearing as a bright horizontal line), while the x axis is the wavelength in Å. The colour bar shows the intensity in units of ergs s^–1cm^–2 Å^–1. Prominent emission lines are denoted. The vertical red lines in the upper panels show the wavelength range of the Hα and [N II] λ6583 Å lines, which is further zoomed in on in the lower panels.