The Rosette Nebula (NGC 2237-8, 46) with star cluster (NGC 2244)

Object: NGC 2237-8, 46 (nebula, Caldwell 49), NGC 2244 (open cluster, Caldwell 50)
Type: Emission nebula
Constellation: Monoceras
Distance: 4900 light years

Date: February 23rd, 24th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 36 x 300s H-alpha, 15 x 200s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

The Rosette Nebula (also known as Caldwell 49) is a large H II region located near one end of a giant molecular cloud in the Milky Way galaxy region lying in the constellation of Monoceros.  The nebula has an apparent diameter of over a degree, more than twice the diameter of the full moon.  The open cluster NGC 2244 (Caldwell 50) is embedded within the nebulosity, and is easily seen in a small telescope.  The nebulosity itself is too faint to be seen visually from suburban skies, however.

The constellation of Monoceros is rather dim and ill-defined, lying to the east of its brilliant neighbour Orion.  The location of the Rosette is shown on the Stellarium sky map below:

Interestingly, recent research suggests that the shape of the Rosette nebula is a disc that is (rather fortuitously) orientated face-on to our Earth, rather than a sphere. 

Radiation from the hot young stars of NGC 2244 is sweeping out the gas from the centre of its parent nebula, an effect that can be quite easily seen in the above image.  Researchers at the University of Leeds have found that this cavity is far smaller than it should be given the age and mass of the cluster stars, and have proposed that a combination of magnetic field orientation and a disc-shaped cloud best accounts for the current appearance of the nebula.

The cluster and nebula measure roughly 130 light years in diameter.  The radiation from the cluster stars within the nebula causes the surrounding rarefied gases to fluoresce, producing the visible emission nebula.  The mass of the nebula is estimated to be around 10,000 solar masses.

A survey of the nebula with the Chandra X-ray Observatory has revealed the presence of numerous new-born stars inside the Rosette Nebula.  Altogether, approximately 2500 young stars lie in this star-forming complex.  Most of the ongoing star-formation activity is occurring in the dense molecular cloud to the south east of the bubble.

In his excellent book The Caldwell Objects, Steve O’ Meara corrects the still-widespread errors regarding the discovery and cataloguing of the Rosette Nebula. O’Meara credits the discovery of the Rosette’s central cluster, NGC 2244, to William Herschel, who unambiguously recorded the object in 1784.  The surrounding nebulosity was not seen by the eagle-eyed Herschel, but was discovered later in a piecemeal fashion – a testament to the faintness of it.  Albert Marth discovered a part of the bright north-west segment of the nebula (NGC 2238) in 1864, with E.E. Barnard recording a larger part of the same quadrant in 1883 (although Lewis Swift had actually observed it several years earlier).  In 1886, Swift found the bright patch of nebulosity in the eastern quadrant of the Rosette (NGC 2246), but it was not until the early 1890’s that photography showed the full extent of the nebula.

My image clearly shows the dark Bok globules that are strewn across the face of the Rosette.  The “globules” comprise of gas and dust, slowly coalescing from the surrounding nebula under its own forces of gravitational attraction, and are thought to be the birthplace of new stars and planets.

One of these curious areas, which stands out in the northern arch of the Rosette, resembles a leaping cat.  I’m not sure it has a common name or designation, but I have picked it out in the hydrogen alpha image stack, shown above.

I think the whole nebula resembles the skull of a fossilised pre-human, such as pithecanthropus, with the cluster NGC 2244 sitting in its left eye socket.

Colour image processing for the main image was conducted using my usual methods in AstroArt and PaintShop Pro, which are detailed here.

This is a bit of an improvement on my first attempt at imaging this object some 12 years ago. 

NGC 884 and NGC 869: The Double Cluster...

Objects: NGC 884 and NGC 869 (The "Double Cluster", Caldwell 14)
Type: Open Clusters
Constellation: Perseus
Distance: 7500 light years

Date: February 14th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 20 x 300s luminance, 12 x 200s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

Known since antiquity, the “Double Cluster” was catalogued in 130 BC by Greek astronomer Hipparchus, who referred to it as a “nebula” or “cloudy spot”, one of the half a dozen then recognized.  The starry nature of the clusters remained a mystery until the invention of the telescope in the early 1600’s.

Now known respectively as h and chi Persei, or NGC 884 (to the east, or left, of the image) and NGC 869 (the cluster to the west, or right, of the image), the clusters themselves are separated by only a few hundred light-years and contain stars much younger and hotter than the Sun. 

In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product of the same star-forming region.  NGC 869 has a mass of 3700 solar masses and NGC 884 weighs in at 2800 solar masses; however, later research has shown both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses. 

Based on their individual stars, the clusters are relatively young, both 12.8 million years old.  There are more than 300 blue-white super-giant stars in each of the clusters.

Discernible with the naked eye under dark skies, NGC 869 and NGC 884 occupy an area of sky approximately one degree across, each cluster being physically around 35 light years across. Binoculars are required to see the two clusters as separate entities from suburban skies. Telescopically, this is one of the most popular of objects for visual astronomers. It forms the “sword handle” of Perseus, as shown in the Stellarium star chart below:

This particular evening was clear but a bright gibbous moon was parked high in the sky, thus ruling out any attempt at faint nebulous objects. Processing was straightforward, with the RGB stacks combined in Astroart to give a colour image with pleasing and contrasting star colours. Some of the brighter stars have haloes, possibly caused by reflections from the RGB filters: Pixinsight acolytes would no doubt sneer at such things, but I quite like the effect.

Addition of the stacked luminance data as a luminance layer in PaintShop gave the final image above.  I used a star mask to just slightly drop the luminance and sharpen the stars surrounding the two clusters, just to get the clusters to stand out from the starry background a bit more.

IC 443: The Jellyfish Nebula...

Object: IC 443
Type: Supernova remnant
Constellation: Gemini
Distance: 5000 light years

Date: February 10th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 16 x 600s H-alpha, 6 x 150s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

Discovered on September 25th, 1892 by German astrophotographer Max Wolf, IC 443 is a supernova remnant in the constellation Gemini, produced by a supernova explosion thought to have occurred between 3,000 and 30,000 years ago.  Physically, the nebula is about 70 light years across. Visually it appears to be approximately 50 arc-minutes across, an area of sky just under twice the apparent size of the full moon.  It is not readily seen in backyard telescopes.

The location of IC 443 is shown in the Stellarium sky chart below, just to the east of the third magnitude star Eta Geminorium (named Propus, the bright orange star to the right of the image).

Observations from the Chandra X-ray observatory show that the explosion that created the Jellyfish Nebula may have also formed a peculiar object located on the southern edge of the remnant, called CXOU J061705.3+222127, or J0617 for short. The object is likely a rapidly spinning neutron star, or pulsar, representing the end stage of a star with between 1.4 and 3 solar masses  

When a massive star runs out of thermonuclear fuel, it implodes, forming a dense stellar core called a neutron star.  The outer layers of the star collapse toward the neutron star then bounce outward in a supernova explosion.  

A spinning neutron star that produces a beam of radiation is called a pulsar.  The radiation sweeps by like a beacon of light from a lighthouse and can be detected as pulses of radio waves and other types of radiation.

The comet-like shape of the diffuse X-ray emission suggests motion towards the lower right of the image.  The structure is also evidenced at visible wavelengths, as highlighted in the hydrogen alpha image below:

The orientation of the “line” is about 50 degrees away from the direction expected if the pulsar was moving away from the centre of the supernova remnant in a straight line.

This misalignment has cast some doubt on the association of the pulsar with the supernova remnant. 

However, it is thought that this misalignment could also be explained by movement towards the left of material in the supernova remnant pushing J0617's cometary tail aside.



Seeing conditions and atmospheric clarity were excellent on this particular evening. I was able to grab 16 hydrogen alpha frames before the dreaded "meridian flip" (where the object crosses the east/west line, requiring the telescope to be spun round to prevent it hitting its own pier).  This is a pain and requires the telescope to be re-targetted, although fortunately my set-up usually gets the object back on the CCD chip after the flip, requiring only minor adjustments to re-frame the object on the CCD chip.

Given that the weather forecast was threatening clouds, I decided to grab the RGB frames rather than get more H-alpha data, although 16 subs isn't really enough to beat the background noise down.  My luck held, and I got the last of the blue subs just as a few clouds started to roll in at around midnight.

Colour processing was conducted using the same methods as I used for the Cave Nebula.