Mei, Simona; Blakeslee, John P.; Côté, Patrick; Tonry, John L.; West, Michael J.; in sod. (2007). »The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster«. The Astrophysical Journal. 655 (1): 144–162. arXiv:astro-ph/0702510. Bibcode:2007ApJ...655..144M. doi:10.1086/509598.
Gerhard, Ortwin; Arnaboldi, Magda; Freeman, Kenneth C.; Okamura, Sadanori (2002). »Isolated Star Formation: A Compact H II Region in the Virgo Cluster«. The Astrophysical Journal. 580 (2): L121–L124. arXiv:astro-ph/0211341. Bibcode:2002ApJ...580L.121G. doi:10.1086/345657.
Lea, S. M.; Mushotzky, R.; Holt, S. S. (1982). »Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster«. Astrophysical Journal. 262 (1): 24–32. Bibcode:1982ApJ...262...24L. doi:10.1086/160392.
Mei, Simona; Blakeslee, John P.; Côté, Patrick; Tonry, John L.; West, Michael J.; in sod. (2007). »The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster«. The Astrophysical Journal. 655 (1): 144–162. arXiv:astro-ph/0702510. Bibcode:2007ApJ...655..144M. doi:10.1086/509598.
Gerhard, Ortwin; Arnaboldi, Magda; Freeman, Kenneth C.; Okamura, Sadanori (2002). »Isolated Star Formation: A Compact H II Region in the Virgo Cluster«. The Astrophysical Journal. 580 (2): L121–L124. arXiv:astro-ph/0211341. Bibcode:2002ApJ...580L.121G. doi:10.1086/345657.
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Lea, S. M.; Mushotzky, R.; Holt, S. S. (1982). »Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster«. Astrophysical Journal. 262 (1): 24–32. Bibcode:1982ApJ...262...24L. doi:10.1086/160392.
Ferguson, H. (1997). »Intergalactic Stars in the Virgo Cluster«. HST proposal: 7411. Bibcode:1997hst..prop.7411F.
Mei, Simona; Blakeslee, John P.; Côté, Patrick; Tonry, John L.; West, Michael J.; in sod. (2007). »The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster«. The Astrophysical Journal. 655 (1): 144–162. arXiv:astro-ph/0702510. Bibcode:2007ApJ...655..144M. doi:10.1086/509598.
Gerhard, Ortwin; Arnaboldi, Magda; Freeman, Kenneth C.; Okamura, Sadanori (2002). »Isolated Star Formation: A Compact H II Region in the Virgo Cluster«. The Astrophysical Journal. 580 (2): L121–L124. arXiv:astro-ph/0211341. Bibcode:2002ApJ...580L.121G. doi:10.1086/345657.
Following the entry for M91 in the Connoissance des Temps for 1784, Messier added the following note:
The constellation of Virgo, & especially the northern Wing is one of the constellations which encloses the most Nebulae: this Catalog contains thirteen which have been determined: viz. Nos. 49, 58, 59, 60, 61, 84, 85, 86, 87, 88, 89, 90, & 91. All these nebulae appear to be without stars: one can see them only in a very good sky, & near their meridian passage. Most of these nebulae have been pointed to me by Mr. Méchain. (see M91.)