1. Heiles, C., Habing, H.: 1974, Astron. Astrophys. Suppl. 14, 557
2. Reich, W.: 1982, Astron. Astrophys. Suppl. 48, 219
3. Thonnard, N.: 1980, Annual Report of the Director, Department of Terrestrial Magnetism 1979-1980, 581.
4. Vaucouleurs, G. de, Vaucouleurs, A. de, Corwin, H.G. Jr.: 1976, Second Reference Catalog of Bright Galaxies, Austin: University of Texas Press.