Open Cluster NGC 2194 & Nebulae Sh 2-271/2
History
The open cluster NGC 2194 was discovered by William Herschel on 11 February 1785. He recorded it as VI 5 and described it as follows: «A cluster of very compressed stars, 7 or 8' diameter.» [463]
In 1959 American astronomer Stewart Sharpless published his second catalogue of 313 H-II regions and listed there Sh 2-271 and Sh 2-272 as H II regions. [310] In 1961 Soviet astronomer Vorontsov-Vel'yaminov listed Sharpless 271 as V-V 1-4 and noted: «Very bright in the red, in fact so overexposed that the nucleus is not visible. Size 1.7'x1.8'. Hardly visible near the nucleus in the blue. On the blue print, mpg = 14. The nebula is horseshoe shaped, with a band extending out from the middle. Perhaps it is a planetary nebula.» [390] In 1967 Hromov and Kohoutek listed V-V 1-4 as a type 2 planetary with the designation PK 197-2.1. [391] In 1976 Chopinet and Lortet-Zuckermann doubted that the nebulae Sh 2-271 and 2-272 are planetary nebulae. A low excitation of [O III]/Hβ associated with a detectable radioflux were good arguments in favour of a H II nature. [392]
Physical Properties
| Name | Type | RA (J2000.0) | Dec (J2000.0) | PM [mas/y] | Parall. [mas] | Rvel [km/s] | z | Size ['] | Magnitudes | Identifiers |
|---|---|---|---|---|---|---|---|---|---|---|
| NGC 2194 | OpC | 06h 13m 46s | +12° 48' 47" | 0.535 | 0.263 | 7.5 | 0.000025 | 9 × 9 | B 9.03; V 8.5 | BD+12 1066; C 0611+128; Cl Collinder 87; Cl Melotte 43; NGC 2194; [FSR2007] 0961; [KPS2012] MWSC 0803 |
| Sh 2-271 | HII | 06h 15m 12s | +12° 22' 00" | 2.107 × 2.107 | GRS G197.78 -02.32; PK 197-02 1; PN ARO 177; PN V-V 1-4; PN VV' 40; SH 2-271; [V61] 4 | |||||
| Sh 2-272 | HII | 06h 15m 00s | +12° 20' 00" | B 13.76; V 12.98 | PK 197-02 2; PN Kj 1-1; SH 2-272; [SC93] 84 |
Finder Chart
The open cluster NGC 2194 with the H-II regions Sh 2-271 and Sh 2-272 are located in the constellation Orion. They are best observed in the months of September to May.
Visual Observation
762 mm Aperture: Starting from the fine star cluster NGC 2194, the locations of the two nebulae Sh 2-271 and Sh 2-272 can be explored. Three relatively faint stars, arranged in an isosceles acute-angled triangle, mark the exact positions of the two Sharpless nebulae. Of these, Sh 2-271 is at the apex of the triangle and can only be seen by indirect vision. More surprisingly, the larger and more extended Sh 2-272, which lies at the base of the triangle on the left star, is barely visible or not visible at all. The H-beta filter was the best way to get a glimpse of the two nebulae. We were unsuccessful with UHC and OIII and the fact that the more extended Sh 2-272 could barely be glimpsed also cast doubt on the sighting of the two nebulae. The low SQM value probably also played its part. — 30" SlipStream-Dobson f/3.3, Hasliberg, 27. 12. 2024, SQM-L 20.77, Elena + Eduard von Bergen