We have obtained extensive spectroscopic observations of Nova Cen 1986 at different phases of the event.
From the observed Hα/Hβ line ratio we derived a colour excess EB-V = 0m.54. Using the empirical relationship between the fading time and the absolute magnitude at maximum light as well as the width of the Nal interstellar lines, we estimated for the nova a distance of 1.2 ± 0.2 kpc. The full-width of non-blended lines at the nebular phase indicates an expansion velocity of 1400 ± 120 km s−1
The temporal behaviour of the Hβ emission suggests that the electron density varies with time as Ne ∝ t−3, i.e., the shell evolves more or less homologously. The electron temperature was estimated from the [NII] and [OIII] line ratios. In the O+2 region the electron temperature is in the range 14100 ± 1200 K. The N+ region has a lower temperature, T ≃ 8000 K around day 142 after maximum light. The N+ temperature increases in this region as the shell evolves and attains the same values observed in the O+2 region around days 300-470.