Galactic Nebula Sh 2-128 (Abell 77)


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]

Sh 2-128
Sh 2-128: In visible light (DSS2) and infrared (allWISE) revealing Sh 2-128N [147]

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]

«Strasbourg-ESO Catalogue of Galactic Planetary Nebulae» Acker et al., 1992 [141]
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.

Finder Chart Galactic Nebula Sh 2-128 (Abell 77)
Galactic Nebula Sh 2-128 (Abell 77) in constellation Cepheus. Charts created using SkySafari 6 Pro and STScI Digitized Sky Survey. Limiting magnitudes: Constellation chart ~6.5 mag, DSS2 close-ups ~20 mag. [149, 160]

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