| Emission nebula | |
|---|---|
| H II region | |
 As seen by the DESI Legacy Survey | |
| Observation data: epoch | |
| Right ascension | 17h 19m 48.5s |
| Declination | −39° 20′ 19″[1] |
| Distance | 8,800 ly (2,700 pc) |
| Apparent magnitude (V) | 14.95 [2] |
| Apparent dimensions (V) | 5' |
| Constellation | Scorpius |
| Designations | RCW 121, ESO 333-3, IRAS 17149-3916, Haro 3-6, PN H 2-6[3] |
Sh 2-4 is an emission nebula in the constellation Scorpius. It is part of the Sharpless Catalog assembled by Stewart Sharpless.[4] It was originally misidentified as a planetary nebula. The incorrect planetary designation PN H 2-6 can still be used as an identifier. It may be associated with the star cluster Havlen-Moffat 1.[1]
Visibility
[edit]The nebula is bright, and visible with longer exposure. The nebula mostly emits red light, making viewing through a hydrogen-alpha filter effective.[5]
Structure
[edit]Havlen-Moffat 1 is known to be a source of ionization within Sh 2-4. The nebula contains two Wolf-Rayet stars, designated WR 87 and WR 89.[6] Contained within the nebula is the infrared cluster [DBS2003] 118. [7]
References
[edit]- ^ a b "The Sharpless Observing Atlas" (PDF).
- ^ "Sharpless (Sh2) - Astrobasics". 13 September 2022.
- ^ "RCW 121".
- ^ "CCD Images of the Sharpless Catalog".
- ^ "SH2-4 (Sharpless 4)".
- ^ "RCW 121".
- ^ Dutra, C. M.; Bica, E.; Soares, J.; Barbuy, B. (2003). "New infrared star clusters in the southern Milky Way with 2MASS". Astronomy and Astrophysics. 400 (2): 533. arXiv:astro-ph/0301221. Bibcode:2003A&A...400..533D. doi:10.1051/0004-6361:20030005.
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