Abell 39

Abell 39 is a low surface brightness[2] 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.[4][6] It is estimated to be about 6,800 light-years from earth and 4,600 light-years above the Galactic plane.[2] It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.[2][3]

Note that Abell 39 can also refer to ACO 39, the 39th member of the Abell catalogue of around 4,000 galaxy clusters.

Abell 039
Emission nebula
Planetary nebula
Credit: [Adam Block/Mount Lemmon SkyCenter/University of Arizona]
Observation data: J2000 epoch
Right ascension 16h 27m 33.737s[1]
Declination+27° 54′ 33.44″[1]
Distance6.8 kly (2.1 kpc)[2] ly
Apparent magnitude (V)Integrated: 13.7;[3][4] Central Star: 15.5 ± 0.2[2]
Apparent dimensions (V)155″.1 × 154″.5[2]
ConstellationHercules
Physical characteristics
Radius2.5 ly (0.78 pc)[2][5] ly
Notable featuresAlmost perfectly spherical[3]
DesignationsPN A66 39,[1] PN ARO 180,[1] PK 047+42 1,[1] PN G047.0+42.4, and Abell 39[1]

Central star

Its central star is slightly west of center by about 2″ or 0.1 light-years.[3] 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.[2] 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☉.[2]

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.[2]

The central star is classified as a subdwarf O star.[7]

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.[2]

This planetary nebula has been expanding for an estimated 22,100+1700
−1500 years, based on an assumed expansion velocity between 32 and 37 km/s and a 0.78 parsec radius.[2]

Background galaxies are visible near the nebula, and some can be seen through the translucent nebula.[2]

Oxygen is only about half as abundant in the nebula as it is in our own sun.[3]

Notes
  1. SIMBAD 2008
  2. Jacoby, Ferland & Korista 2001
  3. Darling 2008
  4. Abell 1966
  5. APOD 2005
  6. Abell 1955
  7. Greenstein, Jesse L.; Minkowski, Rudolph (1964). "The Central Stars of Planetary Nebulae of Low Surface Brightness". The Astrophysical Journal. 140 (1): 1601–1603. Bibcode:1964ApJ...140.1601G. doi:10.1086/148064.
gollark: Or sinnerscales.
gollark: In the end, all shall become Neglected.
gollark: Such is the cave. Especially when not paying enough attention.
gollark: I missed a XEnowyrm. Again.
gollark: A crown with the cracked eggs of failed subjects.

References
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