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McSwain, M. Virginia; Gies, Douglas R. (Kasım 2005), "The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters", The Astrophysical Journal Supplement Series, 161 (1), ss. 118-146, arXiv:astro-ph/0505032 $2, Bibcode:2005ApJS..161..118M, doi:10.1086/432757.
Frommert, Hartmut; Kronberg, Christine (21 Ağustos 2007), Messier 18, Students for the Exploration and Development of Space (SEDS), 4 Ekim 2018 tarihinde kaynağından arşivlendi, erişim tarihi: 11 Kasım 2018.
Frommert, Hartmut; Kronberg, Christine (21 Ağustos 2007), Messier 18, Students for the Exploration and Development of Space (SEDS), 4 Ekim 2018 tarihinde kaynağından arşivlendi, erişim tarihi: 11 Kasım 2018.