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| IC 1396A (vdB 142, left) and IC 1396B (centre); The "Elephant's Trunk"... |
Object: IC1396A (vdB 142) + IC1396B
Type: Reflection/emission/dark nebula
Constellation: Cepheus
Distance: 2400 light years
Date: November 18th. and December 7th. 2018
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD
Subframes: 24 x 600s H-alpha, 20 x 600s OIII, 20 x 150s blue (2x2 binned), 30 flats/dark flats per channel, hot pixel removal in Astroart (no main frame darks).
Popularly called the Elephant's Trunk Nebula,
IC1396A and IC1396B are parts of a much-larger
region of faint nebulosity (IC 1396) that lies 2,450 light-years away in the constellation
of Cepheus and which spans an area of over 5 degrees as seen in the sky.
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| Location of IC 1396A in the sky... |
IC 1396A is a bright-rimmed cloud (BRC) on the periphery of
the associated giant H II region IC 1396 produced by the Trumpler 37 star cluster.
Over 250 young stars in and around IC
1396A have been identified, with a spatio-temporal gradient of stars from the
IC 1396A cloud towards the primary ionizing star HD 206267 being found.
The entire IC 1396 H II region (Sh 2-131) is excited mainly
by the star HD 206267 located at the centre of the region (and just out of shot to the left in the above image) in the 4 million year-old
cluster Trumpler 37. IC 1396 has a rich
population of >20 bright-rimmed and cometary globules seen in silhouette
against the emission nebula.
Many of the clouds reside on the large molecular shell
surrounding the H II region, and sites of possible star formation have been
identified in/around at least several globules, including sites of substantial
star formation in IC 1396A.
Lying 15′ west of HD 206267, IC 1396A is the BRC closest in
the sky to HD 206267. Its optical rim is
the brightest of all rims and the cloud is thus likely to be the physically
closest to HD 206267. IC1396B lies slightly to the west of its brighter sister.
A cavity in the molecular cloud is present in the head of
the A globule and contains a pair of young stars (LkHa 349 and LkHa 349c) that
formed from the dense gas in the globule, and which have cleared the spherical
opening within the head of the globule. They provide the glint in the eye of the elephant, as seen in a crop of the above image (below).
These stars can be seen in both optical and Spitzer infrared images. While one of these stars is much fainter than
the other in optical images, they show a similar brightness in the infrared
Spitzer image. This indicates the
presence of a thick and dusty disk around LkHa 349c. These disks, called circumstellar disks, are
the places where planets and moons will likely form in the future. They are much thicker in the early
stages of star formation and glow brightly in infrared.
IC1346A is also designated as vdB 142. The vdB (van den Burgh) catalogue was
originally published in 1966 by Sidney van den Bergh, and referenced 158 reflection
nebulae:
A study of reflection nebulae, van den Bergh, S., 1966. Later it was expanded to 159 objects by René
Racine:
Stars in reflection nebulae, Racine, 1968. The catalogue contains information for all stars
with a spectral classification of BD and CD lying north of -33 deg and which
are surrounded by reflection nebulosity visible on both the blue and red prints
of the Palomar Sky Survey. The nearer
reflection nebulae lie predominantly along Gould's Belt, whereas the more
distant ones are concentrated in the galactic plane.
Gould's Belt itself was first described by Benjamin Gould in
1879 as a collection of bright and massive stars that form a ring in a
projection on the sky. This rings traces
out several molecular clouds in the local part of the galaxy where star
formation is prominent. Gould's Belt is
estimated to have a diameter of 3000 light years.
The hydrogen alpha image (below) shows a detailed mixture of bright and dark nebulosity.
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| IC1396A/B in hydrogen alpha.. |
The OIII and blue channel data show very little data by comparison. The Ha, OIII and blue channels were RGB combined in AstroArt (Ha = red, OIII = green, blue=blue). The RGB image was then exported to PaintShop Pro and curve adjusted, with the Ha channel then added back as a luminance overlay. Blue haloes on the brighter stars were manually removed with the colour replacer tool, with final contrast and curves adjustment to give the final image shown at the top of this post.
I also tried a HOO version, using the H-alpha data as the red channel, and the OIII data for green and blue...
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| IC 1396A/B as HOO |
This rendition has the fashionable orientation of north to the right and is fashionably darker. My preference is to try and present deep-sky images in their correct aspect, but in this case the columnal nature of the dust clouds is nicely emphasised. I always think that in this view, the nebula resembles a woman walking away from the field of view...
