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Merrett, et al, H. R.; Merrifield, M. R.; Douglas, N. G.; Kuijken, K.; Romanowsky, A. J.; Napolitano, N. R.; Arnaboldi, M.; Capaccioli, M. et al. (June 2006), “A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph”, Monthly Notices of the Royal Astronomical Society369 (1): 120–142, arXiv:astro-ph/0603125, Bibcode: 2006MNRAS.369..120M, doi:10.1111/j.1365-2966.2006.10268.x
Merrett, et al, H. R.; Merrifield, M. R.; Douglas, N. G.; Kuijken, K.; Romanowsky, A. J.; Napolitano, N. R.; Arnaboldi, M.; Capaccioli, M. et al. (June 2006), “A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph”, Monthly Notices of the Royal Astronomical Society369 (1): 120–142, arXiv:astro-ph/0603125, Bibcode: 2006MNRAS.369..120M, doi:10.1111/j.1365-2966.2006.10268.x