Spectroscopic and photometric observations of the recurrent nova IM Normae

摘要

The outburst of the recurrent nova IM Nor was followed visually and spectroscopically. In the beginning of the outburst, the nova belonged to Williams' Fe II class, but one month later, the spectrum changed to the He/N class. Thus IM Nor is a member of the hybrid class of novae, and has many spectroscopic similarities with CI Aql and T Pyx, the two other slow recurrent novae observed until now. In early February, the radial velocity of the Fe II emission lines was +220 ± 35 km/s, the main absorption had -682 ± 4 km/s, and a faint absorption component -902 ± 1 km/s. The strengths of the interstellar Ca II, Na I, and K I lines as well as those of the diffuse interstellar bands indicate an interstellar extinction E_(B-V) ≥ 0.8 and a distance d ≥ 2.5 kpc. The (uncertain) conclusion is that the absolute magnitude of IM Nor is comparable to that of classical novae of the same speed class.