Galactic Nebula Sh 2-128 (Abell 77)
History
In 1955 the American astronomer George Ogden Abell published a list of 13 globular clusters and the positions of 73 planetary nebulae, where he listed this nebula as number 63 (PN A55 63). Later in 1966 Abell he then published a completed list including the size and description of the 86 planetary nebulae discovered on the POSS photo plates. The nebula was then listed as nebula 77 (PN A66 77). He noted on the nebula: «Appears asn an ellipse with several sections of different brightness.» [331, 332]
In 1959, the American astronomer Stewart Sharpless listed this nebula in his «Catalogue of H II Regions» as Sh 2-128. [310]
In 1968 G. S. Kromov, and L. Kohoutek first published doubts about the planetary nature about this nebula. [185] A study from 1986 by F. Sabbadin et al. then confirmed that Abell 77 was indeed a compact H II region. [232]
Physical Properties
Sh 2-128 resembles a classic planetary nebula, but it is a compact H II region, excited by a O7 star close to its center. The age is estimated to be ~106 years. Few arcminutes north of Sh 2-128 lies Sh 2-128N, a molecular cloud with a younger (less than 3×105 years), active star forming region, visible only in infrared. The distance is estimated to 9.4 kpc. [252]
| Designations | PN G097.5+03.1: A 77, PK 97+03.1, A55 63, ARO 363, Sh 2-128, VV' 551 |
| Right Ascension (J2000.0) | 21h 32m 11s |
| Declination (J2000.0) | +55° 52' 46" |
| Dimensions | 40." (optical) |
| Radial Velocity | -113.4 ± 23.0 km/s |
| Expansion Velocity | 7.5 (O-III) km/s |
| C-Star Designations | AG82 430 |
| C-Star Magnitude | B: 16.86, V: 15.70 |
| Discoverer | ABELL 1955 |
Finder Chart
The nebula Sh 2-128 is in the constellation Cepheus. It is best observed from May to December.
