Last night was the first clear night for a couple of weeks so, despite it being full moon, I decided to set up and have a go at some narrowband imaging. I selected NGC 7635 – Bubble Nebula – as my target as it looks interesting and I haven’t tried imaging it before.
The Bubble Nebula is a HII emission nebula in Cassiopeia, approximately 11,000 lys away and has a radius of around 4 lys. At this time of year it is at around 60 degrees in the eastern sky.
I was initially going to shoot only Hydrogen Alpha (Ha) subs but decided to do an hour of Ha and an hour of Oxygen 3 (O3) to try out processing a bi colour palette.
Set up went fine and my guiding was good with a total error of around 0.7″ in PHD2. The full moon was a problem though – it has given me some data but the SNR isn’t what it needs to be to really process this target. I ended up with 60 mins of Ha and 75 mins of O3 (although the O3 was shot at the end and the last few frames were affected by the light levels rising again pre-dawn.
I also had a couple of problems I need to work on. My coma corrector spacing isn’t quite right yet as I still have ‘rugby ball’ shaped stars near the edges, specifically the top left. I also had some frames download with horizontal banding across them – I have no idea why as the frames on either side were fine. With a large enough data set, I’d have dumped them but I couldn’t with the limited data I caught. I think it has something to do with USB speed settings so I’ll have to revisit that as my laptop uses a PCI-express USB3 card rather than a native port.
The processing was a bit of a pain too – the SNR has made it nearly impossible to drive any real contrast or colour so I opted for a more muted palette that still brings in the reds and blues of Ha and O3.
Still, it’s an image and the nights are getting longer. NGC 7635 will remain in the sky for a few months yet so no doubt I’ll get another crack at it at the end of the summer.
Technical card on Astrobin