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Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A. (January 1983), "Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids", Icarus, vol. 175, no. 1, pp. 141–158, Bibcode:2005Icar..175..141H, doi:10.1016/j.icarus.2004.10.017.
Takir, D.; Hardersen, P. S.; Gaffey, M. J. (March 2008), "The Near-Infrared Spectroscopy of Two M-Class Main Belt Asteroids, 77 Frigga and 325 Heidelberga", 39th Lunar and Planetary Science Conference, (Lunar and Planetary Science XXXIX), held March 10–14, 2008 in League City, Texas. LPI Contribution No. 1391, p. 1084, Bibcode:2008LPI....39.1084T
