Gold Canyon, AZ, December 23, 2022

Since adding a 4” refractor to my telescope collection, I started to image open star clusters.  Photographing open clusters with a 9.25” SCT never produced acceptable results.  Since Cassiopeia was at the meridian after sunset, I imaged four open clusters in a single frame as the first target of three for the night.  I collected data for red, green and blue filters, with 60 second exposures.  With f/5.2 optics, the brighter stars in NGC 663 were still clipped (saturated).   Time was limited by light pollution to the west, waiting for M42 to reach an appropriate altitude, and cloudy nights coming in the near future.  Less than 1 hour was collected for each filter, so this was a test of how few subframes could be acquired and still produce a decent image.

I processed the data using a similar workflow in PixInsight as with other star clusters.  I have grown to love the WeightedBatchPreprocessing script to calibrate and integrate the R, G and B channels.  This time, I gave the new BlurXTerminator tool (from Russ Croman) a try to affect the stars.  BlurXTerminator uses a neural network to perform deconvolution, an inverse filtering method used to recover the original, more idealized input data from the actual images treated as the output of some transformation function.  The results are fantastic, with BlurXTerminator shrinking stars, correcting PSFs, and reducing larger halos.  However, there are some residual halos and chromatic fringes in the bright stars.  This tool is a game changer as described on many YouTube astrophotography channels and websites.  While a bit pricy, it is worth the cost of admission.  So, image processing with three AI-based tools, BlurXTerminator, NoiseXTerminator and StarXTerminator, has been greatly simplified and the resulting images are superior to those processed with other more traditional tools in PixInsight.  With limited integration time, the RGB image had significant  background noise.  NoiseXTerminator with aggressive settings was applied in the linear state.  After stretching, the MultiscaleLinearTransform tool was used to reduce chrominance noise.

This image shows a very rich star field in the Perseus arm of the Milky Way.  There are four open clusters in this single frame.  This area of the Milky Way is rich in dust and gas as evidenced by several dark nebulae and background color differences.

NGC 663 (Caldwell 10) is in the center of the frame.  It is a young open cluster with about 400 stars and spans about a quarter of a degree across the sky.  NGC 663 is about 6,850 light years distant with an estimated age of 20–25 million year.  This cluster appears to be located in front of a molecular cloud, although the two are not physically associated, and the dust blocks the light of more distant members.  This cluster has a high number of Be stars, about 24.  These are spectral class B stars that show prominent emission lines of hydrogen in their spectrum.  Most of the Be stars in the cluster lie between spectral class B0 and B3.  There are at least five blue stragglers in the cluster; stars that formed by the merger of two other stars.  NGC 663 also has two red supergiant stars, both located on its periphery (Wikipedia).

NGC 654 is in the lower right of the frame.  It is 2,830 ly away.  It is a very young cluster, aged approximately 15 million  to 40 million years, with a star formation time spread of at least 20 Myr.  The central region of the cluster shows less reddening than the rest of the cluster.  One explanation is that between the Solar System and the cluster lie two dust layers.  Behind the cluster is one more dust layer.  This cluster has about 80 members, including three Be stars and a few luminous stars (Wikipedia).

NGC 659, the Yin-Yang cluster, is in the lower left of the frame.  It is a young open cluster consisting mostly of a few hot, blue stars.  NGC 659 is about 8000 ly away and spans 6 arcminutes, which corresponds to a diameter of 14 ly (G. Imm).  Caroline Herschel discovered NGC 659 September 27, 1783, with her 4.2" comet-seeker reflector.

IC 166 is in the upper right of the frame.  It is a relatively old open cluster, classified as intermediate age, with an estimated age of 1 billion years.  The cluster is about 15,600 ly from Earth.  Note that the stars are reddish in color, either indicating their age as maturing stars or that the stars are obscured by a cloud of dust and gas.

Imaging details:

Stellarvue SVX102T with SFR0.74 focal reducer (FL = 528mm, f/5.2)
ZWO off-axis guider (OAG-L) with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10C)
Chroma 36mm filters:  Luminance, Red, Green, and Blue
Equatorial camera rotation: 270 degrees

Software:    Sequence Generator Pro, ASTAP plate solving, PHD2 guiding, 
    Losmandy Gemini ASCOM mount control and web client interface,
    SharpCap Pro for polar alignment with the Polemaster camera,
    PixInsight 1.8.9-1 with BlurXTerminator, StarXTerminator, NoiseXTerminator,
    Photoshop CC 2022

Red        1 min x 52 subframes (52 min), Gain 100, Offset 68, 1x1 binning
Green    1 min x 47 subframes (47 min), Gain 100, Offset 68, 1x1 binning
Blue       1 min x 30 subframes (30 min), Gain 100, Offset 68, 1x1 binning

Total integration time: 2.2 hours.