Credit: [Adam Block/Mount Lemmon SkyCenter/University of Arizona]
|Right ascension||16h 27m 33.737s|
|Declination||+27° 54′ 33.44″|
|Distance||6.8 kly (2.1 kpc)|
|Apparent magnitude (V)||Integrated: 13.7; Central Star: 15.5 ± 0.2|
|Apparent dimensions (V)||155″.1 × 154″.5|
|Radius||2.5 ly (0.78 pc)|
|Notable features||Almost perfectly spherical|
|Other designations||PN A66 39, PN ARO 180, PK 047+42 1, PN G047.0+42.4, and Abell 39|
|See also: Planetary nebula, Lists of nebulae|
Abell 39 is a low surface brightness planetary nebula in the constellation of Hercules. It is the 39th entry in George Abell's 1966 Abell Catalog of Planetary Nebulae (and 27th in his 1955 catalog) of 86 old planetary nebulae which either Abell or Albert George Wilson discovered before August 1955 as part of the National Geographic Society - Palomar Observatory Sky Survey. It is estimated to be about 6,800 light-years from earth and 4,600 light-years above the Galactic plane. It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.
Its central star is slightly west of center by about 2″ or 0.1 light-years. This offset does not appear to be due to interaction with the interstellar medium, but instead, it is hypothesized that a small asymmetric mass ejection has accelerated the central star. The mass of the central star is estimated to be about 0.61 M☉ with the material in the planetary nebula comprising an additional 0.6 M☉.
This planetary nebula has a nearly uniform spherical shell. However, the eastern limb of the nebula is 50% more luminous than the western limb. Additionally, irregularities in the surface brightness are seen across the face of the shell. The source of the east-west asymmetry is not known but it could be related to the offset of the central star.
Structure and composition
The bright rim of the planetary nebula has an average thickness of about 10″.1 or about 0.34 light-years. There is a faint halo that extends about 18″ beyond the bright rim giving a complete diameter of around 190″ under the assumption that this emission is uniform around the planetary nebula.
- Abell, George O. (1955), "Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey", Publications of the Astronomical Society of the Pacific 67 (397): 258, Bibcode:1955PASP...67..258A, doi:10.1086/126815
- Abell, George O. (April 1966), "Properties of Some Old Planetary Nebulae", Astrophysical Journal 144: 259, Bibcode:1966ApJ...144..259A, doi:10.1086/148602
- APOD (28 July 2005), Robert Nemiroff (MTU) & Jerry Bonnell (USRA), ed., Abell 39, NASA
- Darling, David (2008), "Abell 39", Internet Encyclopedia of Science
- Jacoby, George. H.; Ferland, Gary. J.; Korista, Kirk T. (10 October 2001), "The Planetary Nebula A39: An Observational Benchmark for Numerical Modeling of Photoionized Plasmas", The Astrophysical Journal 560 (1): 272–286, Bibcode:2001ApJ...560..272J, doi:10.1086/322489
- SIMBAD (5 September 2008), Results for PN A66 39, SIMBAD, Centre de Données Astronomiques de Strasbourg