The Blue Snowball Nebula in Andromeda
The halo shows mostly in OIII. Itís visible but much fainter in Ha, and I only had two Ha frames, so didnít use them. Note the jet at the 6:00 position, as well as several other OIII-bright patches outside the halo from the 4:00 to 9:00 positions. Note also the concentric rings around the core. Rings are seen around a few other bright PN cores, most notably NGC 6543, the Cat's Eye Nebula.
This image is a composite of 20 minute and 2 minute frames using PixInsightís HDR Composite tool. The halo is 20 minute OIII frames, and the core is a mix of 2 minute OIII, red, green and blue frames. OIII was used as luminance and RGB as color for the core. I took 117 two minute Ha frames for the core as well, but adding it in to the core just resulted in some blurring, so I didnít use it. The halo was colorized to teal blue in PixInsight.
Optics/Mount: CPC1100 with f6.3 Celestron reducer on a Milburn wedge. Dec antibacklash set to 27/27. PEC on.
Exposure: Total exposure time about 14 hours; 27 x 20 mins OIII, 117 x 2 mins OIII, 77:60:66 x 2 mins RGB. All bin 1x1.
Filters: Astrodon 5nm Ha and 3nm OIII, Type IIi RGB.
Date: Data was collected over 16 nights in July and August 2013 (short OIII and Ha) and from July to November 2016 (long OIII and Ha, RGB).
Imaging automation and capture: Sequence Generator Pro
Guiding Hardware: ASI120MM, Celestron off axis guider. Guiding scale 0.46 arcsec/pixel. 1 second guide exposures.
Focusing: Rigel Systems GCUSB/nStep on stock C11 focuser
Guiding Software: PHD2. RA aggressiveness 55, hysteresis 0, Minimum Move 1.4 arcsecs, Max RA 200, Max Dec 600. Guiding unbinned with ZWO connection. Dec set to hysteresis. Dithering set to Extreme with Settle < 1.2.
Guiding performance: Fairly poor; FWHM around 2.3 arcsecs.
Light pollution: Bortle 8 (white zone, NELM about mag 4.5)
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.6 arcsecs/pixel (full size)
Processing: Bias, darks, and flats. Stacked and processed with PixInsight, with a few minor modifications in Photoshop.