Richer, Michael G.; Marshall L. McCall (1992). “Planetary nebulae and H II regions in NGC 3109”. The Astronomical Journal103: 54–59. Bibcode: 1992AJ....103...54R. doi:10.1086/116040.
Richer, Michael G.; Marshall L. McCall (1992). “Planetary nebulae and H II regions in NGC 3109”. The Astronomical Journal103: 54–59. Bibcode: 1992AJ....103...54R. doi:10.1086/116040.