Globular Star Cluster M4 and Hydrogen Emission Nebula Sh2-9 by Andrew Klinger, on Flickr
Found within the Rho Ophiuchi Cloud Complex I have framed the Globular Star Cluster M4 next to the much fainter emission nebula Sh2-9. The bright star Sigma Scorpii is both ionizing the red hydrogen gas and also reflecting blue light on the surrounding nebulous dust.
Equipment:
OTA: William Optics GT81 w/0.8x reducer/flattener (382mm fl at f/4.7)
74mm aperture stop-down ring (helps optical flaw by bringing scope to f/5.2)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool
Accessories:
QHYCCD PoleMaster
DeepSkyDad Autofocuser AF1
Software:
SGP
PHD2
PixInsight
Acquisition:
Location: Marathon Motel & RV Park, TX (Bortle 1) for LRGB and Joshua, TX (Bortle 4) for Ha
Dates: 6/15/24, 6/16/24, 7/7/24,
Gain: 76 Offset: 15 (LRGB)
Gain: 200 Offset: 50 (Ha)
Camera temp: -10C
Ha: 86x300" Astrodon 5nm 1.25"
L: 32x180" ZWO 1.25in
R: 17x180" ZWO 1.25in
G: 14x180" ZWO 1.25in
B: 14x180" ZWO 1.25in
Total integration time: 11hr 1min
64x darks per calibration (master from library)
30x flats per calibration
200x bias per calibration (master from library)
Preprocessing:
Batch PreProcessing script to generate calibrated images
StarAlignment
ImageIntegration
DynamicCrop each master
DBE each master
Luminance Processing:
PixelMath to blend Ha in while masking out areas that do not contain Ha
BlurXT
NoiseXT
ArcsinhStretch x2
HistogramTransformation
Created a duplicate enhanced starless version using StarXT
Combined the starless version with the image using PixelMath expression "F=0.4; (1-(1-$T)*(1-s)*F)+($T*~F)". (s=starless photo)
LocalHistogramEqualization
HistogramTransformation
Preparing separate R,G,B masters for combination:
Used PixelMath to blend the Ha master 50% into Red, 7.5% into Green, and 7.5% into Blue channel.
Created HaRGB image with ChannelCombination
HaRGB Processing:
SpectrophotometricColorCalibration
SCNR Green
BlurXT
NoiseXT
ArcsinhStretch x2
HistogramTransformation
CurvesTransformation for slight contrast and saturation
Combined HaRGB with Luminance using LRGBCombination
LHaRGB Processing:
MorphologicalTransformation with starmask to slightly reduce star sizes
NoiseXT
Invert>SCNR Green>Invert with a mask to remove magentas
Resampled to 70% for web posting
