Adelman, S. J. (decembrie 1988), „Elemental Abundance Analyses with Coadded DAO Spectrograms - Part Five - the Mercury-Manganese Stars Phi-Herculis 28-HERCULIS and HR:7664”, Monthly Notices of the Royal Astronomical Society, 235 (3): 763, Bibcode:1988MNRAS.235..763A, doi:10.1093/mnras/235.3.763.
Adelman, S. J. (decembrie 1988), „Elemental Abundance Analyses with Coadded DAO Spectrograms - Part Five - the Mercury-Manganese Stars Phi-Herculis 28-HERCULIS and HR:7664”, Monthly Notices of the Royal Astronomical Society, 235 (3): 763, Bibcode:1988MNRAS.235..763A, doi:10.1093/mnras/235.3.763.