NGC 6960: The Witch, the Broom, and the Witch's Familiar
The Western Veil supernova remnant, also known as the Witch's Broom, North segment
The Veil is in the constellation Cygnus, The Swan, and the Milky Way runs right through it. The Milky Way has around 400 billion stars so the field of view is crowded with the things, foreground stars (the Veil is 2,400 light years away) and in the background. The total exposures are > 10hours, so the camera (which is cooled to -10 oC to reduce noise) goes very deep.
The entire supernova remnant (of which the Witch's Broom is only a part), is a rapidly expanding (400 km/sec) spherical shell of gas smashing into the interstellar gas and dust. The shock wave heats up the gas and causes it to glow. The shell is so thin we only see it edge on as we look through the thickest portions of it.
The Veil Nebula in its entirety is quite large, several degrees across. The full field of view of the scope/camera in this configuration is about 1 degree square, although the pics here have been cropped from the full frame. Colours are the so-called Hubble palette – the emission line filters Sii (deep red), Ha (very dark red), Oiii (mouldy green) are mapped onto Red, Green, Blue channels, hence it is called an SHO mix. This produces a characteristic blue/turquoise and gold motif without too much manipulation. The mix of colours reflects the relative abundance of the elements sulphur, oxygen and hydrogen.
Details:
Veil Nebula, supernova remnant, NGC 6960
Distance: 2,400 lyrs
Diameter: 130 lyrs
Age: 10,000 - 20,000 yrs
Angle subtended: diameter 3 degrees
Magnitude: 7
Constellation: Cygnus, The Swan
Photograph taken in narrowband filters: Ha (656nm), Sii (672nm) and Oiii (501nm). These Astronomik filters about 7nm FWHM. Total exposure time 11.3 hrs.
Ha 1x1 bin - 42x 300s = 3.5hrs, 16-17 June, scope West side, prime focus
Sii 1x1 bin - 46x 300s = 3.8hrs, 23-24 June, scope West side, prime focus
Oiii 1x1 bin - 48x 300s = 4 hrs, 24-25 June, scope West side, prime focus
Rig:
Imaging scope: SW Startravel 150mm F5 Refractor, Baader Diamond Track, (2.5x Celestron Luminos 2inch imaging barlow), Atik 460EX mono
Guide scope: SW Evostar 90mm F10, with guiding XY stage, ZWO 120MM camera
Guiding: 2 stage PHD: high frequency guide scope (mount tracking) and low frequency OAG image train guiding (guidescope flex)
Mount: Home made German Equatorial pillow block mount, permanently rooftop mounted. Spring loaded DEC axis gearing.
Other gadgets: ST4 based anti vibration shutter, ST4 based PEC
Processing:
PixInsight: Lights, Darks, Flats, Biases, Align Calibration, Linear fit, BXT, Channel Combination, SCNR(G). StarNet2 star removal/star layer
GradXpert: Gradient removal
Topaz DeNoise AI: Noise removal
Affinity Photo: 32 bit image processing (curves, high pass masking, selective colour)
