Collinder 399 The Coathanger, header

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. 

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