Category Archives: open clusters

Collinder 399 – The Coathanger

Collinder 399 - The Coathanger and nearby dark nebulaeWithin the constellation of Vulpecula is an asterism catalogued as Collinder 399 (Cr 399, from a catalogue of open clusters published by Swedish astronomer Per Collinder). More commonly, this asterism is called the Coathanger, owing to its appearance  Brocchi’s Cluster, or Al Sufi’s Cluster. 

Despite being considered as a true open cluster for much of the 20th century, this is in fact a random grouping of stars – data on parallaxes and proper motions from Hipparcos (http://articles.adsabs.harvard.edu/full/1998A%26A…340..402B) shows these stars to be a chance alignment rather than any kind of bound cluster. 

To the north (and partly encompassing the Coathanger itself) is a reflection nebula with designation LBN130, while further to the north, located with a background of a larger dark nebula (LDN 767) are another two patches of reflection nebula VdB126/LBN134 and LBN 133. Surrounding the whole area are many members of the LDN (Lynds Catalog of Dark Nebulae) catalogue that block the light from the myriad background stars in the plane of the milky way – these are marked in the associated annotated image. 

Image was taken from Sainte-Nathalène, Perigord, France on evenings of 10th/11th Aug 2018. Camera was QHY163M running at -15C on a Canon 200mm f2.8/L II lens (@f3.85).  Mount was a Losmandy GM8, guided with a 160mm guidescope and ZWO ASI120MM.

Exposure was LRGB using Baader 36mm LRGB filters. Exposures were L=166 (1min sub-exposures); RGB=98:90:88 (2min subs) – totalling 7h22m. All taken at gain 75, offset 27. Image capture using Sequence Generator Pro; processing using Pixinsight. 

Field centred at:
RA: 19h 25m 37s
Dec: +21° 42′ 27″
Up is 358 degrees E of N, field size: 3.98 x 5.3 deg

This image was published in the Gallery section of Astronomy Now, October 2018. 

Merope & Tempel’s Nebula (NGC1435)

Image centred at:
RA: 03° 46′ 18″
Dec: +23° 56′ 04″
Field of view: 25.46′ x 18.82′

Merope & NGC1435 (Tempel's Nebula)The Pleiades open cluster in Taurus is one of the brightest and most recognisable objects int he winter sky. As a first LRGB image using the 14″ Newtonian, and to test the setup of the off-axis guider, I imaged the area around Merope (23 Tau). This was also the first use of a Bahtinov mask that I got laser cut by Oxford Hackspace. The focusing mask works excellently – this should be a real plus, especially for any planetary/lunar work.

The particular area of nebulosity imaged here around Merope was discovered by Wilhelm Tempel on October 19th, 1859, and is catalogued as NGC1435. The dust isn’t in fact the nebula from which the cluster formed, rather that the Pleiades happen to be travelling through a particularly dense part of interstellar medium. This dust scatters blue light from the cluster members, resulting in the reflection nebula visible to us.

The image shows strong diffraction spikes from the secondary spider, as would be expected. There’s also further diffraction visible around the brightest stars dark shadowing present at 60 degree angles, which is the result of the mirror retaining “clips” (they are not actually clips – they are part of the cell in the case of the 9 point Orion Optics mirror cell). To remedy this would require a mask to be added over the outer edge of the mirror to cover these over – this is maybe something I’ll think about making in the future to help deal with tricky situations like this! 

The additional dark shadow pointing to the right appears to be the focuser drawtube intruding on the internal light path inside the scope – that’s probably something that can only be cured by either a shorter drawtube, or shortening the truss tubes. Again. Maybe I’ll wait in case I decide to change coma corrector at some point, in which case it’ll probably need a change to the focal plane position anyway.

The image was taken on the evening of the 7th Jan 2018 through the 14″ (350mm) Newtonian, with an ST2000XM and an MPCC v1 coma corrector. Total exposure was “only” 2h 32m (L: 59m (20x1m, 13x3m), RGB: 31m (10x1m, 7x3m) each channel). Processing in Pixinsight and Photoshop CS4.

M48 – Open Cluster in Hydra

Field centred at (plate solve by nova.astrometry.com):
RA: 08h 13m 48s
Dec: -05° 44′ 32″
Up is 3.32 degrees E of N

M48 - Open Cluster in HydraFaintly visible to the naked eye, M48 is a large open cluster in the sprawling constellation of Hydra, the Water Snake. This was originally one of the “missing” Messier objects – Charles Messier catalogued this object some 5 degrees off in declination, but this cluster was independently observed by Caroline Herschel in 1783 – the connection between the two only being made some 150 years later than Messier’s original observation.

Interestingly, in this image, there is a hint of a nebular structure just to the right (west) of the cluster (about 75% of the way across the frame as shown). It’s hard to see if this is real, or an artefact due to inaccurate flat reduction/reflection – the only way to prove this is by taking deeper exposures, and moving the scope around to ensure no systematic errors. Given the poor weather prior to taking this image, it seems unlikely to happen in the near future!

Images were acquired on 24th March 2017 from West Oxfordshire, using an ST-2000XM through a WO FLT110 on a Losmandy Titan. Exposures were R:G:B = 90:70:70 in 5 min subs, with reduction and processing in Pixinsight and Photoshop. 

M67 – An Old Open Cluster

Field Centred at (plate solve from nova.astrometry.net):
RA: 08h 51m 29s
Dec: +11° 49′ 26″
Up is 90.7 degrees E of N

M67 - Open Cluster in CancerM67 is an open cluster located in Cancer – it is much smaller than it’s larger neighbour M44 (The Beehive Cluster/Praesepe), and while not the oldest open cluster (with an age estimated to be 4 billion years), it is close at about 800-900ly distance.

None of the stars are bluer than F spectral class (with the exception of the 30 or so blue stragglers found in the cluster), and there is limited extinction from dust/soot, which makes it an excellent target for study, along with a similarly useful target in NGC188. 

The set of images taken here was also a first test for a new setup in being able to guide using a newly acquired TS OAG9 – this is a very low profile off axis guider and allows me to guide in front of the filters – while this isn’t always required, it makes holding a guide star much easier, especially for narrowband work where guiding with the guide chip in the camera can be nigh-on impossible! This setup allows me to guide using PHD2 and image using APT (with the advantage of having it’s own focus control and platesolving capabilities, as well as Astrotortilla being able to take images to make platesolving/mount alignment much easier). 

Images were taken on 15th and 20th March 2017 from West Oxfordshire, using the SBIG ST2000XM on a William Optics FLT110 working at |f5.7 with the FLAT4 reducer. Guiding was performed off-axis by my ASI120MM, controlled by PHD2. 

Exposures were:
R:G:B = 90:75:65 (all in 300sec subs). 

Reduction/Processing in Pixinsight and Photoshop CS4.

M36, Carbon Star OW Aur & Holoea

Field Centred at: 
RA: 05h 36m 25s
Dec: +34° 07′ 24″
Up is -89.8 degrees E of N
(Plate solve by nova.astrometry.net)

M36 in AurigaM36 is one of the three bright open clusters in Auriga. It was catalogued by Charles Messier on the night of 2nd Sept 1764, though it had been previously discovered at least 110 years prior to this by Italian astronomer Giovanni Batista Hodierna. Despite being one of the fainter open clusters in Messier’s catalogue (though M38, also in Auriga is the fainter of the three), it is visible with the naked eye from a dark site.

There are about 60 stars in the cluster itself at a distance of about 4100 light years. It is very similar in extent to the Pleiades, and if it was at the same distance, it would likely appear just as bright!

In this image to the lower left (south west – north is to the right here) there is the deep red variable star OW Aur. This is another carbon star, similar to V358 Aur as imaged near to M37

Holoea - YSO in M36
Holoea – YSO in M36

Also of note in the object, though only just visible at this scale (shown at 200% scale on left) is an enigmatic object with the name “Holoea” – this is an object that has a tail like structure with high velocity outflows, and is likely to be a young stellar object. Details on the discovery and analysis of this object can be found at 1996A&A…305..936M (Magnier, E. A.; Waters, L. B. F. M.; Kuan, Y.-J.; Chu, Y.-H.; Taylor, A. R.; Matthews, H. E.; Martin, E. L.)

The data presented here was taken on the evening of 30th Nov 2016 as an opportune target while waiting for another object to be in a favourable position. As such, exposures were fairly short, totalling 45:40:40 R:G:B (all unbinned, 5min sub exposures). Reduction/processing was performed in Pixinsight with final tweaks in Photoshop. During processing in PI, I generated a pseudo-Luminance frame from the combined RGB data and then merged this back to form the LRGB image shown.