Harris, Hugh C.; Dahn, Conard C.; Canzian, Blaise; Guetter, Harry H.; Leggett, S. K.; Levine, Stephen E.; Luginbuhl, Christian B.; Monet, Alice K. B.; Monet, David G.; Pier, Jeffrey R.; Stone, Ronald C.; Tilleman, Trudy; Vrba, Frederick J.; Walker, Richard L. (February 2007). “Trigonometric Parallaxes of Central Stars of Planetary Nebulae”. The Astronomical Journal133 (2): 631–638. arXiv:astro-ph/0611543. Bibcode:2007AJ....133..631H. doi:10.1086/510348.
Su, K. Y. L.; Chu, Y.-H.; Rieke, G. H.; Huggins, P. J.; Gruendl, R.; Napiwotzki, R.; Rauch, T.; Latter, W. B.; Volk, K. (March 2007). “A Debris Disk around the Central Star of the Helix Nebula?”. The Astrophysical Journal657 (2): L41–L45. arXiv:astro-ph/0702296. Bibcode:2007ApJ...657L..41S. doi:10.1086/513018.
Harris, Hugh C.; Dahn, Conard C.; Canzian, Blaise; Guetter, Harry H.; Leggett, S. K.; Levine, Stephen E.; Luginbuhl, Christian B.; Monet, Alice K. B.; Monet, David G.; Pier, Jeffrey R.; Stone, Ronald C.; Tilleman, Trudy; Vrba, Frederick J.; Walker, Richard L. (February 2007). “Trigonometric Parallaxes of Central Stars of Planetary Nebulae”. The Astronomical Journal133 (2): 631–638. arXiv:astro-ph/0611543. Bibcode:2007AJ....133..631H. doi:10.1086/510348.
Su, K. Y. L.; Chu, Y.-H.; Rieke, G. H.; Huggins, P. J.; Gruendl, R.; Napiwotzki, R.; Rauch, T.; Latter, W. B.; Volk, K. (March 2007). “A Debris Disk around the Central Star of the Helix Nebula?”. The Astrophysical Journal657 (2): L41–L45. arXiv:astro-ph/0702296. Bibcode:2007ApJ...657L..41S. doi:10.1086/513018.
Harris, Hugh C.; Dahn, Conard C.; Canzian, Blaise; Guetter, Harry H.; Leggett, S. K.; Levine, Stephen E.; Luginbuhl, Christian B.; Monet, Alice K. B.; Monet, David G.; Pier, Jeffrey R.; Stone, Ronald C.; Tilleman, Trudy; Vrba, Frederick J.; Walker, Richard L. (February 2007). “Trigonometric Parallaxes of Central Stars of Planetary Nebulae”. The Astronomical Journal133 (2): 631–638. arXiv:astro-ph/0611543. Bibcode:2007AJ....133..631H. doi:10.1086/510348.
Su, K. Y. L.; Chu, Y.-H.; Rieke, G. H.; Huggins, P. J.; Gruendl, R.; Napiwotzki, R.; Rauch, T.; Latter, W. B.; Volk, K. (March 2007). “A Debris Disk around the Central Star of the Helix Nebula?”. The Astrophysical Journal657 (2): L41–L45. arXiv:astro-ph/0702296. Bibcode:2007ApJ...657L..41S. doi:10.1086/513018.