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Object of the Week March 16, 2014 - Eight Burst Nebula
NGC 3132, He 2-40, PN G272.1+12.3, PK 272+12.1, Eight Burst, Southern Ring
Planetary Nebula
RA: 10h 07m 1.89
Dec: −40° 26′ 11″
Size: 1.4’
Mag: 9.7v, 8.2p
The Eight Burst Nebula, NGC 3132, is a bright and extensively studied planetary nebula in the constellation Vela. Also known as the Southern Ring Nebula, in Hubble photos it bares a remarkable resemblance to M57, the Ring Nebula. The biggest challenge for many to observing the Eight Burst is its southerly declination of −40°. But even when low on the horizon this one is worth catching, so give it a go.
Hubble Image of the Eight Burst Nebula
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Discovered by Sir John Herschel at the Cape of Good Hope in 1835 with an 18-inch speculum telescope, it was originally cataloged as h3228. Herschel’s discovery log entry reads: “Planetary nebula, very large, very bright, elliptic; has in it a 9th mag star somewhat excentric. Its light is exactly equable, ie. not increasing towards the middle; yet I cannot help imagining it to be closely dotted. It is just like a star out of focus in certain states of the mirror and atmosphere. Three stars near, a = 9th mag; b = 9th mag; c = 14th mag; A very extraordinary object."
H. Shapley and J. S. Paraskevopoulos in “Photographs of Thirty Southern Nebula and Clusters” coined the name Eight Burst Nebula in 1940. Concerning the planetary nebula they say: “A series of photographs of varying exposures would be necessary to bring out the intricate details…. It could well be named the “8-burst” planetary from the number of distinct arcs on the boundary of the main disk or shell”.
Plate III Figure 13 from Lassell, W. (1867) Miscellaneous Observations with the Four-foot Equatorial at Malta. Memoirs R.A.S., 35.
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Unusual among the planetaries is the prominent white 10th magnitude central star. This star is also a known binary, having a 16th magnitude companion, ~1.6" away. Studies show that it is this star, and not the 10th magnitude primary that is responsible for illuminating the nebula. Simply, the presumed progenitor does not produce enough ultraviolet to illuminate the gas. The planetary nebula nucleus is a bright example of the Wolf-Rayet class of stars, having a surface temperature around 135,000°! The nebulosity comprises of a H/He ratio of 12.7%, and an excess of Nitrogen that is higher than most of the other planetaries known. This suggests that the mass of the star was originally about 2.4 Solar Masses, at the lower limit for stars that can produce planetary nebulae.
The Eight Burst Nebula is extremely bright – even for small telescopes in light polluted skies. However for those observers in more northerly latitudes the window of opportunity for observing the planetary is rather limited. Here at 40°N the Eight Burst Nebula is best observed in March and April when it culminates at ~10° above the horizon. That time is rapidly approaching as today’s (March 16, 2014) Full Moon begins to wane towards New Moon on March 30, 2014.
DSS POSS-2 Red Plate FOV 15x15 arc minutes
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Here’s some observation notes from March 2012 through a 17.5” f/ 4.5 reflector. SQM 20.45. “Initial reaction is this is a twin of the nearby Ghost of Jupiter. Large, size is 1 arc-minute. It has a ghostly appearance yet it is surprisingly bright. Somewhat elongated with a clearly defined ring structure. Prominent central star estimated to be Mag 8.”
While researching I found observations of the Eight Burst Nebula made through a wide range of apertures, with the smallest being a 102mm refractor. Of course some observers have a distinct advantage of higher elevation, and/or a more southerly latitude which places the nebula higher in the sky. With an aperture of greater than 12” most reported seeing color (blue or green) and some structure detail within the nebulosity. OIII filters were reported to provide a good improvement.
“GIVE IT A GO AND LET US KNOW”
GOOD LUCK AND GREAT VIEWING!
