Huchra, J. P.; Geller, M. J. (June 15, 1982). "Groups of galaxies. I - Nearby groups". Astrophysical Journal. 257 (Part 1): 423–437. Bibcode:1982ApJ...257..423H. doi:10.1086/160000.
Huchra, J. P.; Geller, M. J. (June 15, 1982). "Groups of galaxies. I - Nearby groups". Astrophysical Journal. 257 (Part 1): 423–437. Bibcode:1982ApJ...257..423H. doi:10.1086/160000.
P. Veron; A. C. Goncalves; M. P. Veron-Cetty (1997). "AGNs with composite spectra". Astronomy and Astrophysics. 319: 52–66. Bibcode:1997A&A...319...52V.