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Hodge, Paul W.; Gurwell, Mark; Goldader, Jeffrey D.; Kennicutt, Robert C., Jr. The H II regions of M101. I - an atlas of 1264 emission regions. Astrophysical Journal Supplement Series. August 1990, 73: 661–670. Bibcode:1990ApJS...73..661H. doi:10.1086/191483.