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Coordinates:
17h 13m
44.211s, −37° 06′ 15.94″ NGC
6302 (also called the Bug Nebula or
Butterfly Nebula), is a bipolar planetary nebula in the constellation
Scorpius. It is one of the
most complex planetary nebulae observed. The spectrum of
NGC 6302 shows its central star is one of the hottest objects in
the galaxy, with a surface temperature in excess of 200,000 K,
implying that the star from which it formed must have been very
large.
The central star has never been observed and is
surrounded by a particularly dense equatorial disc composed of gas
and dust. This dense disc is postulated to have caused the star's
outflows to form a bipolar structure (Gurzadyan 1997), similar to an hour-glass. This bipolar structure shows
many interesting features seen in planetary nebulae
such as ionization walls, knots and sharp edges to the lobes.
Observation
history
As it is included in the New General Catalogue, this
object has been known since at least 1888. [6] The
earliest known study of NGC 6302 is Edward Emerson Barnard who, in
1907, drew and described it. (Meaburn et al.
2005)
Since then it has been the focus of many works and displays many
interesting characteristics worthy of study. Interest in recent
years has shifted from discussions over the excitation method in
the nebula (shock-excitation or photo-ionisation) to the properties
of the large dust component.
It was among some of the first images released after the final
servicing mission of the Hubble Space Telescope in September of
2009. [7].
Characteristics
NGC 6302 has a complex morphology which may be approximated as
bipolar with two primary lobes, though there is evidence for a
second pair of lobes that may have belonged to a previous phase of
mass loss. A dark lane runs through the waist of the PN obscuring
the central star at all wavelengths. Observations of NGC 6302
suggest that there may be an orthogonal skirt (or chakram) similar to that found
in Menzel 3. (Meaburn et al.
2005). The nebula is orientated at an angle of 12.8° against
the plane of the sky.
This PN contains a prominent North-West lobe which extends up to
3′.0 away from the central star and is estimated to have formed
from an eruptive event around 1,900 years ago. It has a circular
part whose walls precisely follow a Hubble-type outflow (where
outflow speed is proportional to distance from the central source).
At an angular distance of 1′.71 from the central star, the flow
velocity of this lobe is measured to be 263 km/s. At the
extreme periphery of the lobe, the outward velocity exceeds
600 km/s. The western edge of the lobe displays
characteristics suggestive of a collision with pre-existing
globules of gas which modified the outflow in that region. (Meaburn et al.
2005)
Dust
Chemistry
The prominent dark lane that runs through the centre of the
nebula has been shown to have an extraordinary dust chemistry,
showing evidence for multiple crystalline silicates and features
that have been interpreted by some to be the first extra-solar
detection of carbonates. This detection has been disputed, due to
the difficulties in forming carbonates in a non-aqueous
environment. Other solid state features detected include
crystalline water ice and quartz.
One of the most interesting characteristics of the dust detected
in NGC 6302 is the existence of both oxygen-rich (i.e. silicates)
and carbon-rich (i.e. poly-aromatic-hydrocarbons or PAHs) material.
Stars are usually either O-rich or C-rich, the change from the
former to the latter occurring late in the evolution of the star
due to nuclear and chemical changes in the star's atmosphere. When
a star or nebula is observed to have a dual chemistry it is
indicative of a recent change from O-rich chemistry to C-rich
chemistry.
Notes
References
- APoD (June 2, 1998), Astronomy Picture of the
Day, NASA and Michigan Technological University (MTU), <http://antwrp.gsfc.nasa.gov/apod/ap980602.html>
- APoD (May 5, 2004), Astronomy Picture of the
Day, NASA and Michigan Technological University (MTU), <http://antwrp.gsfc.nasa.gov/apod/ap040505.html>
- Gurzadyan, Grigor A. (1997),
written at Germany, The Physics and Dynamics of Planetary
Nebulae, Springer, 3, ISBN 3-540-60965-2
- Meaburn,
J.; J. A. López & W. Steffen et al. (2005), "The Hubble-Type Outflows from
the High-Excitation, Polypolar Planetary Nebula NGC 6302",
The Astronomical Journal 130 (5):
2303-2311, <http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AJ....130.2303M>
- SIMBAD (January 11, 2007), Results for NGC
6302, SIMBAD, Centre de Données Astronomiques de
Strasbourg, <http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=NGC+6302>
External
links
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See also: Stewart Sharpless · RCW catalog · Gum catalog · Nebula |
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See
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Gum Catalog |
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Colin Stanley
Gum |
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See
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Nebula |
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