NGC 246 (also known as the Skull Nebula[4]orCaldwell 56) is a planetary nebula in the constellation Cetus. It is the first known planetary nebula to have a hierarchical triple star system at its center.[6] The nebula and the stars associated with it are listed in several catalogs, as summarized by the SIMBAD database.[1] NGC 246 was discovered by William Herschel in 1785.
| Emission nebula | |
|---|---|
| Planetary nebula | |
| |
| Observation data: J2000 epoch | |
| Right ascension | 00h47m 03.338s[1] |
| Declination | −11° 52′ 18.94″[1] |
| Distance | 1,600 ly |
| Apparent magnitude (V) | 8[2] / 11.8 (central star)[1] |
| Apparent dimensions (V) | 3.8′[2] |
| Constellation | Cetus |
| Physical characteristics | |
| Radius | 2-3[3] ly |
| Designations | Skull Nebula,[4] Pac-Man Nebula,[5] Caldwell 56, HIP 3678, PMN J0047-1152, 2E 178, PN VV 4, IRAS 00445-1207, MCT 0044-1208[1] |
| See also: Lists of nebulae | |
The nebula is roughly 1,600 light-years away.[7] NGC 246's central star is the 12th magnitude[7] white dwarf HIP 3678 A.[8]
NGC 246 is not to be confused with the Rosette Nebula (NGC 2337), which is also referred to as the "Skull."[9] Among some amateur astronomers, NGC 246 is known as the "Pac-Man Nebula" because of the arrangement of its central stars and the surrounding star field.[5]
In 1785, William Herschel discovered NGC 246.
In 2014, astronomers discovered a second companion to NGC 246's central star, HIP 3678 A, which has a comoving companion star called HIP 3678 B.[6] The second companion star, a red dwarf known as HIP 3678 C, was discovered using the European Southern Observatory's Very Large Telescope.[6]
Media related to NGC 246 at Wikimedia Commons