Catalina, AZ, December 13-29, 2023

This very faint supernova remnant (SNR G166.0+04.3 or LBN 769) is located in the constellation Auriga about 3.5o from the bright star Capella.  It is also called the Rice Hat nebula named for its shape.  Sh2-224 is about 14,700 light years from Earth.  The glowing ionized hydrogen in red and oxygen in cyan are caused by the expanding shockwave of material ejected from the extremely violent explosion when a very large star collapsed at the end of its life.  The material is colliding with clouds of gas in space causing the faint glow.  Many older supernova remnants exhibit the filament structures in the image, similar to those in the very bright Veil nebula.

This object was challenging for several reasons: 1) the Hydrogen-alpha and Oxygen-III are very faint, requiring many hours of integration time to boost the signal to noise ratio, and 2) I collected much of the data during the full moon cycle.  The full moon prevented imaging of almost all of my planned targets in Auriga, Orion and Monoceros.  So, I attempted to image Sh2-224 hoping the moonlight would not affect the narrowband filters beyond an increase in the background.  However, some of the moonlight found its way into the optics and created a large, bright pattern across 1/3 of the image.  I tried to use the 50% of the Ha and OIII subframes with no moonlight “corruption”, but the noise level was too high to process away.  I then included all the subframes to see if GraXpert could remove the moonlight patterns.  The AI mode failed and left many wavy artifacts.  I created a dense grid around the patterns and GraXpert did remove most of the moonlight patterns.  However, there were remaining artifacts that forced me to use PixInsight’s CloneStamp tool over a large portion of the image.  Even with all the subframes, the Ha and OIII masters were very noisy.  I understand why many better astrophotographers acquire significantly more data.  I also removed most of the background surrounding the supernova remnant after stretching the HOO color image and its extracted luminance.  The result was not very satisfying.  I will have to wait for next fall/winter to add more Ha and OIII as the clouds and rain in Western Oregon seem endless.

Imaging details:

Stellarvue SVX102T refractor with 0.74x focal reducer (FL = 528mm, f/5.2)
ZWO large off-axis guider with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10C)
Chroma 36mm Hydrogen-alpha, Oxygen-III, Red, Green, and Blue filters
Equatorial camera rotation: 90 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 a Polemaster camera,
    PixInsight 1.8.9-2,
    Photoshop 2024

Hydrogen-a 10 min x 48 subframes (480 min), Gain 100, Offset 32, 1x1 binning
Oxygen-III  10 min x 57 subframes (570 min), Gain 100, Offset 32, 1x1 binning
Red             1 min x 45 subframes (45 min), Gain 100, Offset 32, 1x1 binning
Green          1 min x 42 subframes (42 min), Gain 100, Offset 32, 1x1 binning
Blue            1 min x 42 subframes (42 min), Gain 100, Offset 32, 1x1 binning

Total integration time: 19.7 hours