M27 – The Dumbbell Nebula – Dual Narrowband – 23/08/2019
It’s been a few months since I last imaged due to the lack of any real night – in the mid summer, it never really gets dark enough to image well, even in the dead of night! Once August rolls around, however, the advent of reasonably warm, dewless nights, means that this is a lovely time of year to image. The main drawback is the thing that makes the nights so pleasant – the heat. This makes it a bit harder for the cooled CCD to maintain a low temperature on the sensor. The result is a little noisier than it is on cooler nights, but as long as you collect enough data, then the end results are usually good, as the Sony sensor in the Atik 314L is very low noise anyway.
Here’s my first image of this season, Messier 27, the Dumbbell nebula in the constellation of Vulpecula, at a distance of about 1227 light years. I’ve always reckoned it looks more like an apple core than a dumbbell… This is a lovely object to look at visually, and the cloudy ‘apple core’ shape can be seen in even quite small telescopes.
It’s a planetary nebula, meaning it’s a shell of material that’s been shed by a central star. This is what’s known as a dual-narrowband image, where I’ve captured the Hydrogen Alpha and Oxygen III (Ha and OIII) emissions from the object and combined them into a colour image by mapping them to visible colours. This gives what is actually a false colour image strictly speaking, but shares the characteristics of the object visually. This is about four and a bit hours of exposure in total, with about two hours each of Ha and OIII.
Processed to show a reasonably natural end result by using the Ha in the red channel, and the OIII in the green and blue channels. This is an object that’s quite good for this treatment as it is bright in both these emission bands. The mapping of the bands to RGB here is 1:1:1 (Ha:OIII:OIII).