Sh 2-4

Sharpless 2-4

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 dimensions (V)	5'
Constellation	Scorpius
Designations	RCW 121, ESO 333-3, IRAS 17149-3916, Haro 3-6, PN H 2-6 [2]
See also: Lists of nebulae

Sh 2-4 is an emission nebula in the constellation Scorpius. It is part of the Sharpless Catalog assembled by Stewart Sharpless. ^[3] 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

The nebula is bright, and visible with longer exposure. The nebula mostly emits red light, making viewing through a hydrogen-alpha filter effective. ^[4]

Structure

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. ^[5] Contained within the nebula is the infrared cluster [DBS2003] 118. ^[6]

References

1. https://www.astromaster.org/oggetti/sharpless_data/Sharpless_r.pdf
2. "RCW 121".
3. "CCD Images of the Sharpless Catalog".
4. "SH2-4 (Sharpless 4)".
5. "RCW 121".
6. 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.