Abell 70
RA/Dec (J2000): 20h 31m 33s, −07° 05′ 21″ (deepskycorner.ch)
Constellation: Aquila (deepskycorner.ch)
Historical / Contextual Notes
- Discovered by George O. Abell in 1955 from the Palomar Observatory Sky Survey plates. (deepskycorner.ch)
- In Abell’s 1966 follow-up paper, it is listed as Abell 70. (deepskycorner.ch)
- It is visually striking because of a “diamond ring” effect: a background galaxy (PMN J2033-0656) lies behind a portion of the nebula’s northern edge, giving a bright “ring + galaxy” appearance. (deepskycorner.ch)
Physical & Observational Properties
| Property | Value / Description |
| Angular size (optical) | ~ 42″ across (optical shell). (deepskycorner.ch) |
| Distance from Earth | Estimated between ~2.4 to ~3.5 kiloparsecs (~7,800 to 11,400 light-years) depending on study. (deepskycorner.ch) |
| Radial velocity | Approaching us at about −79 km/s (blue-shifted) (deepskycorner.ch) |
| Expansion velocity | ~38 km/s (from [O III] emission line measurements) (deepskycorner.ch) |
| Morphology | Annular / ring nebula; slightly elongated. The shell is faint; bright in [O III] lines. (deepskycorner.ch) |
| Central star system | Binary: hot white dwarf + G-type subgiant (barium-enhanced) companion. The companion is chromospherically active, rotates with ~2.06-day period. (iac.es) |
| Chemical type | Type I planetary nebula: elevated helium and nitrogen abundances. (arXiv) |
Key Significance
- The “diamond ring” effect (nebula + background galaxy) makes it a popular target for imaging and public outreach. (deepskycorner.ch)
- Its central binary with a barium star provides important insights into mass transfer and nucleosynthesis: how s-process elements and carbon in AGB stars can pollute a companion. (arXiv)
- Because it is relatively faint and diffuse, observations require decent apertures and often narrowband filters to pick up faint [O III] emission. (deepskycorner.ch)
References
DeepSkyCorner: Abell 70 with Galaxy PMN J2033-0656. (deepskycorner.ch)
Miszalski, B., Boffin, H. M. J., Brown, A. J., Zak, J., Hume, G. et al. (2011). A barium central star binary in the Type-I diamond ring planetary nebula Abell 70. MNRAS. (arXiv)
“A detailed study of the barium central star of the planetary nebula Abell 70”, Jones, D. et al. (2022). (iac.es)