Robinson, L. E. (June 2002), "Photometry of Five Difficult Asteroids: 309 Fraternitas, 366 Vincentina 421 Zahringia, 578 Happelia, 959 Anne", The Minor Planet Bulletin, 29: 30–31, Bibcode:2002MPBu...29...30R.
Pilcher, Frederick (January 2015), "Rotation Period Determinations for 275 Sapientia, 309 Fraternitas, and 924 Toni", Bulletin of the Minor Planets Section of the Association of Lunar and Planetary Observers, vol. 42, no. 1, pp. 38–39, Bibcode:2015MPBu...42...38P.
