Gurzadyan, G.A. (1976). «Two-photon emission in planetary nebula IC 2149». Publications of the Astronomical Society of the Pacific. 88: 891. Bibcode:1976PASP...88..891G. doi:10.1086/130041.
Gurzadyan, G.A. (1976). «Two-photon emission in planetary nebula IC 2149». Publications of the Astronomical Society of the Pacific. 88: 891. Bibcode:1976PASP...88..891G. doi:10.1086/130041.