The area surrounding the Southern Cross (Crux) and Coal Sack nebula is replete with large areas of Ha that was originally thought to be left over from previous supernova events. Subsequent work however indicates that this large Ha shell is being powered by the Centaurus OB association. The image posted here is centred around an object from the Cederblad catalogue, Cederblad 122, a catalogue compiled by Sven Cederblad and published in 1946. The catalogue  was developed as part of a thesis investigating geometrical properties of diffuse galactic nebulae and contains a list of 215 objects. I stumbled across this area and catalogue whilst wandering around Stellarium looking for my next imaging target.

What I didn't realise until I was further into my research and started processing the data is that this area is part of what is known as the "Coalsack Loop". This object was first identified and included in a paper by Walker and Zealy published in the Astronomical Society of Australia Journal  (Vol 15, #1) in 1998. The authors were conducting a Ha survey with a view to identifying supernova remnants. The Coalsack loop surrounds the Coalsack nebula and covers a field of approximately 10 degrees. 

I found two renditions of this object here on Astrobin, one in Ha by John Gleeson and an LRGB Ha/OIII/SII version by Mathew Ludgate. Both fine examples of images taken of this area. My attempt here is a little further to the east and south of Matthew's image so I can see myself heading into a mosaic project to capture more of this area.

Data captured for this image was LRGBHa with all processing completed in Pixinsight 1.8.9. Camera used was the ZWO ASI6200 full frame CMOS combined with a Canon EF200mm prime lens delivering a 10 degree field of view. This is a good combination for capturing these widefield areas. To integrate the Ha into the LRGB image I used the NBRGBCombination script as a first pass and then combined this with the LRGB image using a star mask. This process helps to maintain correct star colours whilst integrating the Ha into the final image.

For the presentation in this post I have provided the LRGB image as the mouse over which helps to demonstrate just how much Ha there is in this region. Hover over the image to reveal the LRGB image underneath. Part of the Coalsack Nebula can be seen at the bottom of the image, just right of centre adjacent to the Jewel Box cluster (Kappa Crucis - NGC4755) which is sneaking into the bottom of the image. The bright blue star on the bottom left corner is Beta Muscae. Image revision I is a screen shot from the Sky Safari Pro app showing the location of Ced 122 in the field of view.