Buta, Ronald J. Galactic rings revisited - I. CVRHS classifications of 3962 ringed galaxies from the Galaxy Zoo 2 Database. Monthly Notices of the Royal Astronomical Society. 2017, 471 (4): 4027–4046. Bibcode:2017MNRAS.471.4027B. arXiv:1707.06589. doi:10.1093/mnras/stx1829.
Buta, Ronald J. Galactic rings revisited - I. CVRHS classifications of 3962 ringed galaxies from the Galaxy Zoo 2 Database. Monthly Notices of the Royal Astronomical Society. 2017, 471 (4): 4027–4046. Bibcode:2017MNRAS.471.4027B. arXiv:1707.06589. doi:10.1093/mnras/stx1829.
Schweizer, Francois; Ford, W. Kent; Jedrzejewski, Robert; Giovanelli, Riccardo. The Structure and Evolution of Hoag's Object. The Astrophysical Journal. 1987, 320: 454. Bibcode:1987ApJ...320..454S. doi:10.1086/165562.
Buta, Ronald J. Galactic rings revisited - I. CVRHS classifications of 3962 ringed galaxies from the Galaxy Zoo 2 Database. Monthly Notices of the Royal Astronomical Society. 2017, 471 (4): 4027–4046. Bibcode:2017MNRAS.471.4027B. arXiv:1707.06589. doi:10.1093/mnras/stx1829.
Schweizer, Francois; Ford, W. Kent; Jedrzejewski, Robert; Giovanelli, Riccardo. The Structure and Evolution of Hoag's Object. The Astrophysical Journal. 1987, 320: 454. Bibcode:1987ApJ...320..454S. doi:10.1086/165562.