Homunculus Nebula
| Nebula | |
|---|---|
 |
|
| Observation data: J2000 epoch | |
| Right ascension | 10h 45m 03.6s |
| Declination | −59° 41′ 04″ |
| Distance | 7,500 ly |
| Apparent magnitude (V) | 6.21 (-0.8–7.9) (including the central star) |
| Apparent dimensions (V) | 18" |
| Constellation | Carina |
| Physical characteristics | |
| Radius | 0.29 ly |
| Notable features | Bipolar nebula |
The Homunculus Nebula is a bipolar emission and reflection nebula surrounding the massive star system Eta Carinae, about 7,500 light-years (2,300 parsecs) from Earth. The nebula is embedded within the much larger Carina Nebula, a large star-forming H ii region. From the Latin meaning Little Man, the Homunculus is effectively a small H ii region, with gas shocked into ionised and excited states. It also absorbs much of the light from the extremely luminous central stellar system and re-radiates it as infra-red (IR). It is the brightest object in the sky at mid-IR wavelengths.
Within the Homunculus is a smaller Little Homunculus, and within that a shell of shocked material from stellar winds that has been called Baby Homunculus.
In 1914, Eta Carinae was reported to have a faint companion and also be non-stellar: "fuzzy".
Observations in 1944 and 1945 showed a somewhat elongated nebulosity around 5" wide and 10" long. It was recognised to be expanding consistent with having originated in an explosion in the mid 19th century, measured at 3".2 - 7".5 per century. At that time the shape of the nebula showed a central bulge with a single large lump to the NW and two smaller extensions to the SE, which was described as a Homunculus. Other observations at around the same time described a strongly orange (Hα) central region in a larger fainter green (O iii) nebulosity. The phrase "red spade-beard" was applied, but this name didn't catch on.
The Homunculus consists of two lobes, referred to as NW and SE based on their orientation as seen from Earth, each approximately 7" wide by 5" long. There is also a ragged equatorial skirt of material which can be seen faintly in deep images at certain wavelengths. The lobes are mostly hollow with the material strongly concentrated towards the poles.
The equatorial skirt appears to contain material of the same age and younger than the lobes. It contains a much smaller mass of material than the lobes, shining mainly by reflected light which escapes most easily at equatorial latitudes. There is less dust and little molecular hydrogen compared to the lobes.
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