Little dumbbell nebula
|Little dumbbell nebula|
|Designation|| Messier 76|
NGC 650/NGC 651
|Right ascension||01h 42m 24s|
|Declination||+51° 34′ 31″|
|Type of object||Planetary nebula|
|Magnitude|| Apparent Mag: +10.1|
Absolute Mag: +0.7
|Distance from Earth||2,500 ly|
|Radial velocity||-19.1 km/s|
The Little dumbbell nebula (M76, NGC 650/NGC 651) is a planetary nebula in the constellation of Perseus. It has two designations in the New General Catalogue as it was originally thought to be two separate objects. The name arises from it great similarity to the Dumbbell nebula, though it appears somewhat smaller in telescopes. One of the four planetary nebulae in Messier's catalogue, along with the Dumbbell nebula, the Ring nebula and the Owl nebula. The nebula's small size on the night sky and its faintness makes it one of the most difficult Messier objects to observe. It is visible with binoculars, but is better seen with a telescope. The nebula is also occasionally known as the Barbell nebula of the Cork nebula. It is also sometimes called the "Butterfly nebula" though the name "Butterfly nebula" normally refers to NGC 6302.
The Little dumbbell nebula was first observed by Pierre Méchain on September 5, 1780. Charles Messier added it to his catalogue the following month on October 21. Later in 1787, William Herschel conjectured that the nebula was in fact a double nebula and gave each component a different designation. Subsequently, this was repeated when John Dreyer compile the New General Catalogue in 1888, giving the two supposed nebulae the identifiers NGC 650 and NGC 651. William Huggins used spectroscopy to show the nebula is composed gas in 1866, containing Nebulium lines. Issac Roberts noted similarities to the Ring nebula in 1891 but it was not until 1918 that Heber Doust Curtis classified the nebula as a planetary nebula. Issac Roberts also showed that it was a single and not a double nebula.
Properties and Structure
Its apparent diameter of around 2 arcseconds corresponds to a physical diameter of 1.23 light years. There is great disagreement in the distance to the nebula, some sources suggest it is 1,700 light years, others as much 15,000 light years. The central ring of gas is expanding at around 42 km/s A large but faint halo, with a size of 190 arcseconds, surrounds the nebula. Two stars are believed to be at the centre of the nebula, one with a magnitude of 15.9 and an estimated temperature of 60,000 K. The nebula is thought to have a temperature of some 88,400 K.
Unusually for a nebula, it is brighter visually (magnitude 10.1) than photographically (magnitude 12.2). This is because much of the light emitted by the nebula is in green 5007 Angstrom forbidden line of doubly ionized oxygen, [O III], which our eyes are very sensitive to.