Coma spectra. Left: a 30-min exposure beginning at UT 00:07 September 21. The spectrum is the sum of rows 18–21 and the flux is given for a slit area of 0.1°× 1.2° (48 × 580 m² projected on the nucleus). The red line is a synthetic spectrum of 200 eV electron impact on H₂O (see text). Right: a 50-min exposure beginning at UT 00:54 September 23. The spectrum is the sum of rows 14–17 and the flux is given for a slit area of 0.05° × 1.2° (24 × 580 m² projected on the nucleus). A synthetic spectrum of solar induced fluorescence for a CO column density of 5 × 10¹³ cm^-2 is shown in blue.