Broad-band infrared photometry of the Nova Cygni 1975=the V 1500 Cyg

The results of J, K, L, M, N photometry obtained from Aug. 29, 1975 to June 1976 are presented. Their analysis leads to the value of the shell radius=800 Sun radii for the maximum brightness, absolute magnitude Msub(k)=-10sup(m).2, distance 1.1-1.2 kpc, shell mass=(1-5)10-5 Sun mass, electron number density 1010 cm-3. Hypotheses on the nature of infrared excess 5 μ and the absence of dust shell are discussed. Spectra in 0.6-2.5 μ spectral range, obtained at the maximum brightness, are presented; they show a fast evolution of strong emissions. The strongest emission in 1.0-2.5 μ spectral range is the Pashen series line Pp (lambda 1.28μ) and He line (lambda 1.083μ). Hsub(α), Psub(v), Psub(e), 0177,72,018446 lines as well as some nonidentified lines are present. Radiation in emission lines considerably exceeds radiation in continuous spectrum already soon after the maximum