Flux and position spectra for 2010 and 2013 near 4.63 μm. In the upper panel, the blue curve is the flux spectrum of TX Psc in 2010, the green curve the spectrum of the early type standard HIP 116928. In the lower panel, the blue curve is the flux spectrum of TX Psc in 2010, and the grey curve is the spectrum in 2013. The CO lines used in this analysis are identified, the grey rectangles indicate regions affected by telluric absorption. All spectra have been shifted to the wavelength scale of 2013, therefore the telluric absorptions are red-shifted by about 0.0005 μm in the lower panels. The plus signs and crosses correspond to the position spectra at PAs of 0° and 180°, respectively, for the 2010 (upper panel) and 2013 (lower panel) data. Note the tilde-shaped profiles in the position spectra of the stellar CO lines and the strong photocentre deviation in the telluric lines. The behaviour of the position spectra in the marked lines is almost identical at the two epochs.