| Nebula | |
|---|---|
 Sh-279 as taken from theMount Lemmon Observatory[1] | |
| Observation data: J2000.0epoch | |
| Right ascension | 05h 35m 16.2s[2] |
| Declination | −04° 47′ 07″[2] |
| Distance | 1,500 ly |
| Apparent magnitude (V) | 7.0 |
| Apparent dimensions (V) | 40′×25′ (1977)arcmins |
| Constellation | Orion |
| Physical characteristics | |
| Radius | ~7.5 ly (1977), 2 ly (1975) 1 ly (1973) ly |
| Designations | Sh-279, NGC 1977-73-75 |
| See also:Lists of nebulae | |
Sh 2-279 (alternatively designatedS279 orSharpless 279) is anHII region and bright nebulae that includes areflection nebula located in the constellationOrion. It is the northernmost part of theasterism known asOrion's Sword, lying 0.6° north of theOrion Nebula. The reflection nebula embedded in Sh 2-279 is popularly known as theRunning Man Nebula.[1][3]
Sh 2-279[2] comprises threeNGC nebulae,NGC 1973,NGC 1975, andNGC 1977[4] that are divided by darker nebulous regions. It also includes theopen cluster NGC 1981. The brightest nebulosity, later listed as NGC 1977, was discovered byWilliam Herschel in 1786. He catalogued it as "H V 30" and described "!! 42 Orionis and neb[ula]". The two smaller reflection nebulae were first noted by German astronomerHeinrich Louis d'Arrest, NGC 1973 in 1862 and NGC 1975 in 1864.[5] All three were included in theNew General Catalogue in 1888.[6] The designation NGC 1977 is used in various sources for the reflection area around 42 Orionis (the south-east portion of the reflection nebula), for the entire reflection nebula (including NGC 1973 and NGC 1975), or for the whole nebula complex.[5]
This whole region in Orion's Sword was also later catalogued asOrion 1c. In 1966, van den Bergh distinguished the weak clustering of reflection nebulae that includes Sh 2-279 asOri R2.[7] Every reflection nebula appearing within theSharpless catalogue was first identified on blue plates of thePalomar Sky Survey, and then double checked against the red plates to eliminate possible plate faults. Van den Berg found that there was a strong concentration of newT Tauri stars around theOrion Nebula, tapering off into a tail approaching Sh 2-279.[7]
The Running Man Nebula is a popular target foramateur astrophotographers, as it lies close to theOrion Nebula and has many nearby guide stars. The outline of the running man shows up primarily in photographs; it is difficult to perceive visually through telescopes, though the reflection nebula itself is visible in small to medium apertures in dark skies.
The whole reflection nebula region is likely excited by the hot young star (YSO) called c Orionis,42 Orionis or HD 37018[8] in NGC 1977,[9] which appears as a 4.6 magnitude star some 3.8′ from the centre of Sh 2-279. (See image box.) Other massive stars include the yellow giant 45 Orionis and the variable KX Orionis.[10]
One candidateproplyd was discovered in NGC 1977 with theHubble Space Telescope in 2012. The object showed a bentprotostellar jet and a possible ionization front facing42 Orionis, suggesting it is a proplyd.[11] In 2016 a group of astronomers discovered six proplyds with the Hubble Space Telescope and one proplyd with theSpitzer Space Telescope. The proplyds are pointing to theB-star 42 Orionis, which is the main source ofultraviolet radiation in this region. This ultraviolet light isphotoevaporating theproto-planetary disks and the stellar wind of 42 Orionis is shaping the gas into cometary tails. Proplyds were first discovered in large numbers in theOrion Nebula, but there the ultraviolet source responsible for the photoevaporation is theO-type starTheta1 Orionis C. 42 Orionis is the first instance of a B-type star being responsible for the photoevaporation.[9]
All proplyds in NGC 1977 lie within 0.3 parsec of 42 Orionis and two have resolved central sources in the Hubble images, which might be the disks with radii of about 70 and 48astronomical units.[9]
NGC 1977 also includes the young star Parengo 2042 (P 2042).[12]
{{cite journal}}: CS1 maint: multiple names: authors list (link)