IC 1396A (vdB 142) & IC1396B - The Elephant's Trunk...

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.

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.

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...

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...

The Cave Nebula (Sharpless 2-155)

The Cave Nebula (Sh2-155)

Object: Sharpless 2-155 (Caldwell 9)

Type: Emission nebula
Constellation: Cepheus
Distance: 2400 light years

Date: November 2nd. 2018 (Ha), 17th (RGB)
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 40 x 250s H-alpha (2x2 binned), 20 flats, hot pixel removal in Astroart (no darks). 10 x 250s (2x2 binned) each for RGB

The Cave Nebula is part of an extensive region of ionised hydrogen gas associated with the Cepheus B giant molecular cloud.  The ionisation is caused by radiation from a group of young, hot stars hidden within the dust cloud, which knocks hydrogen electrons into "excited" states that re-emit radiation and cause the surrounding low-pressure hydrogen gas to glow.  Sh2-155 is just a small part of an extensive area of nebulosity in the Cepheus/Cassiopeia region that includes several notable emission nebulae.  It lies about 3.5 degrees south of iota Cephei...

The evening of November 2nd. was clear but the atmosphere was very unsteady. I decided to run the Atik camera in 2 x 2 "binned" mode, partly to make autoguiding accuracy less critical and also because the Cave Nebula is extremely faint and I didn't fancy spending hours getting enough 20 or 30 minute subs to beat down the background noise.

However, this loses a bit of resolution, but the poor seeing would have done that anyway. The seeing did make focussing a bit hit and miss however, and I should really have looked at the first couple of subs a bit more closely.  When I finished the session and downloaded the images next day, I was frustrated to find that the stars were out of focus, with some showing a "doughnut appearance".  At this point I would normally delete them and wait for another imaging opportunity, but clear, moon-free nights at reasonably civilised hours are an extremely rare occurence in my part of the world, so I decided to see if the situation was redeemable.

The Cave Nebula in H-alpha

Fortunately, a couple of software routines in Astroart (Digital Development followed by a few iterations of Lucy-Richardson deconvolution using a mild Gaussian point spread function, for the record) were able to pull the star and nebulosity details back into a reasonably decent shape.  A bit brightness and contrast adjustment (using "curves") and noise removal (mild edge-preserving smooth), both in PaintShop Pro, gave the Hydrogen alpha image above.

I did try and get some hydrogen beta data, but 300 second exposures at 2x2 binning revealed not a jot of nebulosity in the area, so I guess this object just doesn't emit in this part of the spectrum.

It was a couple of weeks before I was able to get some RGB data to make up a colour image.  250 second subs (2x2 binned) through Baader red, green and blue filters were stacked, aligned and RGB combined in Astroart to give this rather disappointing RGB image...

RGB - Cave Nebula area

Whilst the star colours were fine, there was hardly any trace of nebulosity visible. I guess a 60% waxing moon and shortish subs washed out the contrast.  Clearly, I would not be able to directly use the H-alpha frame as a luminance layer, as the lack of any nebula colour in RGB would just result in coloured stars on a grey nebula.

I decided to colourise the existing H-alpha frame by pasting it on to a red background in "Hard Light" mode in PSP.  This gave a bright red nebula image with white stars...

The brighter H-alpha regions tend to remain washed out and so I prepared a second mask as above, but combining in "multiply" mode. This gave a completely red nebula with red stars...

"Colourised" H-alpha frame...

Selecting the bright area (with a feather of about 20 pixels), I pasted and aligned the area over the "Hard Light" image.  With careful use of the eraser tool in PSP and a partial blending (around 50%) it was possible to greatly reduce the remaining washed-out H-alpha regions...











Pasting this over the RGB stars in "lighten" mode at around a 70% blend gave a reasonable mix of star and nebula colour,  A few tweaks to the final colour and contrast using curves gave the final result you can see at the top of this post.

OK, never a NASA APOD, but given the poor quality of data I don't think it turned out too bad.