Object of the Week January 11, 2015 - NGC 1360 A Dissolving Planetary
NGC 1360, Minkowski 1-3, PK 220-53 01, PN G220.3-53.9, Bennett 15
Type III Planetary Nebula
RA: 03h 33m 14.6s Dec: -25° 52’ 17.9”
Size: 11’ x 7.5’
Mag: 9.4v
Surface Brightness: 21.9 mag/arc-second2
Mag (central star): 11.3v
Huge and bright through the winter night
Yet not even plotted on all maps of the sky
In Fornax this object lies
Where mostly galaxies reside
Irregular, peculiar, uncommon they write
Looks more like a football with a distinctly green light
A planetary nebula this happens to be
Has NGC 1360 been seen by thee?
Among the multitude of galaxies in the constellation Fornax, there lurks one of the brightest planetary nebula of the night skies, NGC 1360. How the prolific observers of the period, like John Herschel and James Dunlop, missed this large, bright object remains a mystery to this day. Instead it was two well-known comet hunters, Lewis Swift and Friedrich August Theodor Winnecke, who independently discovered NGC 1360.
The story of Lewis Swift’s discovery is rather interesting. In 1855 Swift purchased a damaged 3-inch objective from a peddler for five dollars. After making a brass mounting and an eyepiece for the telescope he began a survey of the night sky. Two years later he discovered the extremely comet-like glow of NGC 1360. Meanwhile Friedrich Winnecke is credited as a co-discoverer of NGC 1360 when he observed it with his 3.5” comet seeker telescope in January 1868.
These early discoverers of NGC 1360 both described the object as a peculiar object, not at all sure what it was. It wasn’t until 1946 when Rudolph Minkowski first identified it as a planetary nebula. It was Lubos Kohoutek who labeled it an “uncommon planetary” in 1968. A few years later Steven Hynes listed NGC 1360 in his Planetary Nebulae as a Type III planetary (a planetary with an irregular disk).
Today we know that NGC 1360 is typical of a large evolved planetary nebula, where evolved means “aging”. A 2004 paper Physical Structure of Planetary Nebulae. III. The Large and Evolved NGC 1360 describes the planetary nebula as not having any obvious shell morphology, unlike most planetary nebulae that show distinctive, well-marked symmetry, and well-defined boundaries. The authors go on to show that the large kinematic age (study of stellar movement used as a proxy for age) of the shell, which is ~10,000 years, and the low density of the nebula, imply that NGC 1360 has begun to merge (dissolve) with the interstellar medium.
NGC 1360 is one of the few known examples of a large, high-excitation planetary. The central star’s spectrum places it in the Wolf-Rayet category of planetary nebulae, meaning the central star appears to be in a state of flux and is violently ejecting matter into the surrounding shell. The bright (magnitude 11.3) central star has a temperature that is over 14 times hotter than the Sun and 540 times more luminous. It is a hot sub-dwarf with only one-tenth the Sun’s diameter and a bit over half of its mass.
Despite all these unusual characteristics, the object’s green hue, caused by oxygen excited by the hot central star, marks NGC 1360 as a planetary nebula. In photographs a faint red smudge to the northeast of the nebula can be seen, probably traces of material ejected before it became a true planetary nebula.
NGC 1360 is not only bright it is huge. While many planetaries measure arc-seconds across, this one spans nearly 11 arc-minutes (major axis), making its apparent size five times larger than M57, the Ring Nebula. Its size and brightness make it a fairly easy object to find. Just don’t let its location in Fornax put you off as being too far south. The planetary is no farther south than the globular cluster M4 near Antares.
bennett15.jpg
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Observations of the NGC 1360 have been recorded with apertures as small as 2.2”. Of course your mileage will vary based on your sky conditions. Increasing aperture begins to show the full glory of this planetary. It responds quite well to an O-III filter, which brings out an incredible amount of extremely subtle detail. By the way, you are excused if you begin to think the planetary nebula looks like a spiral galaxy.
How many of you have viewed this huge, diffuse, green football-shaped planetary nebula? Better hurry before it totally dissolves into the interstellar medium!
“GIVE IT A GO AND LET US KNOW”
GOOD LUCK AND GREAT VIEWING!
P.S. Curiously the second edition of Star Atlas 2000.0 doesn't plot NGC 1360
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