Sh2-279 (alternatively designated S279 or Sharpless 279) is an

HII region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

and bright nebulae that includes a

reflection nebula Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in s ...

located in the constellation Orion. It is the northernmost part of the asterism known as

Orion's Sword Orion's Sword is a compact asterism in the constellation Orion. It comprises three stars (42 Orionis, Theta Orionis, and Iota Orionis) and M42, the Orion Nebula, which together are thought to resemble a sword or its scabbard. This group is so ...

, lying 0.6° north of the

Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae and is visible to the naked eye in the nig ...

. The reflection nebula embedded in Sh2-279 is popularly known as the Running Man Nebula. Sh2-279 comprises three NGC nebulae, NGC 1973, NGC 1975, and NGC 1977 that are divided by darker nebulous regions. It also includes the

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

NGC 1981. The brightest nebulosity, later listed as NGC 1977, was discovered by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...

in 1786. He catalogued it as "H V 30" and described "!! 42 Orionis and neb la. The two smaller reflection nebulae were first noted by German astronomer

Heinrich Louis d'Arrest Heinrich Louis d'Arrest (13 August 1822 – 14 June 1875; ) was a German astronomer, born in Berlin. His name is sometimes given as Heinrich Ludwig d'Arrest. Biography While still a student at the University of Berlin, d'Arrest was pa ...

, NGC 1973 in 1862 and NGC 1975 in 1864. All three were included in the

New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and ...

in 1888. 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. This whole region in Orion's Sword was also later catalogued as Orion 1c. In 1966, van den Bergh distinguished the weak clustering of reflection nebulae that includes Sh2-279 as Ori R2. Every reflection nebula appearing within the Sharpless catalogue was first identified on blue plates of the

Palomar Sky Survey Palomar may refer to: Places * Any of several locations in San Diego County, California: ** Palomar Mountain ** Palomar Observatory, located on Palomar Mountain ** Palomar College in San Marcos, California ** Palomar Medical Center in Escondido, ...

, and then double checked against the red plates to eliminate possible plate faults. Van den Berg found that there was a strong concentration of new

T Tauri T Tauri is a variable star in the constellation Taurus, the prototype of the T Tauri stars. It was discovered in October 1852 by John Russell Hind. T Tauri appears from Earth amongst the Hyades cluster, not far from ε Tauri, but it i ...

stars around the

, tapering off into a tail approaching Sh2-279. The Running Man Nebula is a popular target for amateur astrophotographers, as it lies close to the

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.

Ionization Source

The whole reflection nebula region is likely excited by the hot young star (YSO) called c Orionis,

42 Orionis 42 Orionis is a class B1V (blue main-sequence) star in the constellation Orion. Its apparent magnitude is 4.59 and it is approximately 900 light years away based on parallax. The primary star, Aa, has one spectroscopic companion Ab of m ...

or HD 37018 in NGC 1977, which appears as a 4.6 magnitude star some 3.8 from the centre of Sh2-279. (See image box.) Other massive stars include the yellow giant 45 Orionis and the variable KX Orionis.

Proplyds in NGC 1977

One candidate

proplyd A proplyd, short for ionized protoplanetary disk, is an externally illuminated photoevaporating protoplanetary disk around a young star. Nearly 180 proplyds have been discovered in the Orion Nebula. Images of proplyds in other star-forming region ...

was discovered in NGC 1977 with the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

in 2012. The object showed a bent protostellar jet and a possible ionization front facing

, suggesting it is a proplyd. In 2016 a group of astronomers discovered six proplyds with the Hubble Space Telescope and one proplyd with the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

. The proplyds are pointing to the B-star 42 Orionis, which is the main source of

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

radiation in this region. This ultraviolet light is photoevaporating the proto-planetary disks and the stellar wind of 42 Orionis is shaping the gas into cometary tails. Proplyds were first discovered in large numbers in the

, but there the ultraviolet source responsible for the photoevaporation is the O-type star Theta¹ Orionis C. 42 Orionis is the first instance of a B-type star being responsible for the photoevaporation. 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 48

astronomical units The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

. NGC 1977 also includes the young star Parengo 2042 (P 2042).

Image gallery

Image:Orion Nebula LRGB 2.jpg, Image of the Running Man nebula and its proximity to the Orion nebula. NGC 1977 proplyds zoom.png, Largest

in NGC 1977 seen by Hubble File: NGC1977_CDK_Large03.jpg, NGC 1977, Running Man Nebula, by W4SM using 17" PlaneWave CDK, Louisa, VA

References

External links

*
Sharpless 279 at Galaxymap
{{NGC20 Orion (constellation) NGC objects Orion molecular cloud complex Reflection nebulae Star-forming regions Sharpless objects