1. Alter, G., Ruprecht, J., & Vanisek, J. 1970, in Catalogue of Star Clusters and Associations, ed. G. Alter, B. Balázs, & J. Ruprecht
2. The extremely young open cluster NGC 6611:
Compiled catalogue, absorption map and the HR diagram
3. Binney, J., & Tremaine, S. 1987, in Galactic Dynamics, Princeton, NJ: Princeton University Press (Princeton series in astrophysics)
4. Binney, J., & Merrifield, M. 1998, in Galactic Astronomy (Princeton, NJ: Princeton University Press, Princeton series in astrophysics)