Cygnus Loop - AbsoluteAstronomy.com

The Cygnus Loop is a large supernova remnant

Supernova remnant

A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...

(SNR) in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

Cygnus

Cygnus (constellation)

Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...

, an emission nebula measuring nearly 3° across. Some arcs of the loop, known collectively as the Veil Nebula
Veil Nebula
The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus. It constitutes the visible portions of the Cygnus Loop , a large but relatively faint supernova remnant...

or Cirrus Nebula, emit in visible light. Radio, infrared and X-ray images reveal the complete loop.

Visual components: the Veil Nebula

The visual portion of the Cygnus Loop is known as the Veil Nebula, also called the Cirrus Nebula or the Filamentary Nebula. Several components have separate names and identifiers, including the "Western Veil" or "Witch's Broom", the "Eastern Veil", and Pickering's Triangle.

NGC 6960

NGC 6960, the Western Veil, is the western part of the remnant, also known as the "Witch's Broom", located at J2000 RA

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

Dec

Declination

In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

. As the western-most NGC object in the nebula (first in right ascension

Right ascension

), its number is sometimes used as an NGC identifier for the nebula as a whole.

NGC 6992, NGC 6995, and IC 1340

These three luminous areas make up the Eastern Veil. NGC 6992 is an HI shell located along the north-eastern edge of the loop at J2000 RA

Right ascension

Dec

Declination

. NGC 6995 is located farther south at J2000 RA

Right ascension

Dec

Declination

, and IC 1340 even farther south at J2000 RA

Right ascension

Dec

Declination

Pickering's Triangle

Also known as Pickering's Wedge, or Pickering's Triangular Wisp, this segment of relatively faint nebulosity was discovered photographically in 1904 by Williamina Fleming

Williamina Fleming

-External links:* * * * from the Astronomical Society of the Pacific- Obituaries :*...

at Harvard Observatory, where Edward Charles Pickering

Edward Charles Pickering

Edward Charles Pickering was an American astronomer and physicist, brother of William Henry Pickering.Along with Carl Vogel, Pickering discovered the first spectroscopic binary stars. He wrote Elements of Physical Manipulations .Pickering attended Boston Latin School, and received his B.S. from...

was director at the time. The Triangle is brightest along the northern side of the loop, though photographs show the nebulosity extending into the central area as well.

NGC 6974 and NGC 6979

These two objects are generally identified today (as by the NGC/IC Project and Uranometria) with two brighter knots of nebulosity in a cloud at the northern edge of the loop, to the east of the northern edge of Pickering's Triangle. NGC 6979 was reported by William Herschel

William Herschel

Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...

, and while the coordinates he recorded for Veil objects were somewhat imprecise, his position for this one is tolerably close to the knot at J2000 RA

Right ascension

Dec

Declination

.

The identifier NGC 6979 is sometimes taken to refer to Pickering's Triangle, but the Triangle is probably not what Herschel saw or what the Catalogue intended for this entry: it was discovered only photographically, after the Catalogue was published, and long after Herschel's observation.

NGC 6974 was reported by Lord Rosse

William Parsons, 3rd Earl of Rosse

William Parsons, 3rd Earl of Rosse, Knight of the Order of St Patrick was an Irish astronomer who had several telescopes built. His 72-inch telescope "Leviathan", built 1845, was the world's largest telescope until the early 20th century.-Life:He was born in Yorkshire, England, in the city of...

, but the position he gave lies in an empty region inside the main loop. It was assumed that he recorded the position incorrectly, and the New General Catalogue

New General Catalogue

The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...

gives Rosse's object as the other knot in the northern cloud, located at J2000 RA

Right ascension

Dec

Declination

, one degree north of Rosse's position. These filaments in the north-central area are sometimes known as the "carrot". The spectrum at 34.5 MHz of the region associated with NGC 6974 ranges straight over the entire frequency range 25 to 5000 MHz.

Southeastern knot

The southeastern knot is located at J2000 RA

Right ascension

Dec

Declination

on the southeastern rim of the Cygnus Loop. The knot has been identified as an encounter between the blast wave from the supernova and a small isolated cloud. The knot is a prominent X-ray feature, consisting of a number of filaments correlated with visual line emission. By combining visual and X-ray data, it can be shown that the southeastern knot is an indentation on the surface of the blast wave, not a small cloud but the tip of a larger cloud. The presence of a reverse shock is evidence that the knot represents an early stage of a blast wave encountering a large cloud.

Distance

Until recently the distance to the supernova remnant was estimated at about 2500 light-years. Recent studies, however, have shown that it must be closer. In 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

images) with direct line-of-sight measurements of the radial expansion towards the Earth. He concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.

This revised calculation, though it involved some uncertainty and was met with some resistance, has been substantially corroborated by the discovery via the Far Ultraviolet Spectroscopic Explorer

Far Ultraviolet Spectroscopic Explorer

The Far Ultraviolet Spectroscopic Explorer is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins program...

(FUSE) of a star behind the Veil. The star, KPD2055+3111, of spectral type sdOBwas, was identified as UV-bright in an image from the Ultraviolet Imaging Telescope, and absorption lines in its spectrum indicate that its light is partially intercepted by the supernova remnant. The emission properties of the star indicate that it lies about 1860 ly away, giving an upper bound for the distance of the loop and supporting the previous estimate of 1470 ly.

The revised distance in turn yields revised estimates of the size of the remnant (to 90 ly, down from 150 ly previously) and for its age (now thought to be between 5000 to 8000 years).

Astronomical ultraviolet source

The brightest far-ultraviolet sources of the Cygnus Loop occur in the north-east edge of the remnant. The first flight of the High Resolution Emission Line Spectrometer (HIRELS), a wide-field, far-ultraviolet nebular spectrometer, tuned to OVI emission lines, was launched aboard a Nike-Black Brant from White Sands Missile Range

White Sands Missile Range

White Sands Missile Range is a rocket range of almost in parts of five counties in southern New Mexico. The largest military installation in the United States, WSMR includes the and the WSMR Otera Mesa bombing range...

to observe the Cygnus Loop, the first observed galactic OVI emission line source.

X-ray source

The X-ray source Cygnus X-5 coincides with SNR G074.0-08.6 (the Cygnus Loop), located at J2000 RA

Right ascension

Dec

Declination

, observed by Uhuru

Uhuru (satellite)

Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...

at 4U 2046+31. This source also has catalogue numbers 1E 2049.4+3050, 1H 2050+310, and 1M 2051+309, having been observed by the Einstein Observatory

Einstein Observatory

Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...

, HEAO 1, and OSO 7

OSO 7

OSO 7 is the seventh in the series of American Orbiting Solar Observatory satellites launched by NASA between 1962 and 1975...

, respectively.

The Cygnus Loop is a strong source of soft X-rays.

The center of the supernova shell as determined from X-ray data lies at J1950 RA

Right ascension

Dec

Declination

. A characteristic thermal temperature averaged over the loop from X-ray spectral data is T_x = 2.9 ± 1.5 x 10⁶ K. An X-ray surface brightness map of the loop was obtained with a one-dimensional X-ray telescope flown aboard an Aerobee 170 sounding rocket

Sounding rocket

A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, where to sound is to throw a weighted line from a ship into...

launched on March 30, 1973, from the White Sands Missile Range

White Sands Missile Range

External links

Sharpless Catalog 103

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Visual components: the Veil Nebula

NGC 6960

NGC 6992, NGC 6995, and IC 1340

Pickering's Triangle

NGC 6974 and NGC 6979

Southeastern knot

Distance

Astronomical ultraviolet source

X-ray source

See also

External links