Walton, Oregon
January 28, February 24 and 25, 2022

This project was a lesson in frustration, and I was reluctant to post it.  First, western Oregon had nothing but clouds and rain for several months; not untypical but depressing none the less.  Second, the few nights with clear skies during the January and February dark moon phases were very windy and cold, and transparency and seeing varied significantly.  Next, to compensate for the seeing, I tried an experiment by using 2x2 binning on the ZWO ASI2600MM Pro camera for the first time.  At a remote dark sky site in the coast range, I set up my rig using my pickup truck cap, stacked with equipment cases on top, as a wind shield.  This proved reasonably effective, and the Losmandy G11 mount was solid, but the Celestron 9.25” SCT was still sensitive to strong gusts.  One night of three had good seeing and transparency with the wind picking up later in the night.  It was very cold, so I had to huddle in the cab of my truck until the wind became too strong.  The cold and fierce wind made equipment packing a not so fun experience.  Prior to imaging NGC 2403, I cleaned the C9.25 corrector plate and mirrors.  I recollimated the secondary mirror, but I did not do a fine collimation.  Finally, the 2x2 binned data was very blotchy.  The ASI 2600 with 1x1 binning has always produced low noise images, so I was perplexed when it became very difficult to reduce this “noise” in PixInsight using the same workflow I have always used for galaxies.  This first version of the image still appears noisy even with fairly aggressive noise reduction in the background.  Noise is visible in the faint dust in the arms of the galaxy and crisp details are missing.

With a limited amount of high-quality data, I plowed ahead with processing in PixInsight.  After numerous attempts to denoise the integrated linear channel images, I eventually resampled by 2x each channel (Ha, Lum, R, G, B).  I also struggled with creating starless images.  Starnet2 was recently released and produced so-so Ha, RGB and Luminance starless images in the linear (unstretched) state.  StarXTerminator with AI training weights version 7 did a better job but removed some of the galaxy core.  Luckily, StarXTerminator with AI version 8 just came out and it did produce a good result in linear and stretched states.  Galaxies are challenging objects for star removal with bright cores and star forming regions, and with stars, especially bright ones, in front of the galaxy.  StarXTerminator removed the stars with few artifacts and little removal of the galaxy core.  The competition between the developers of StarNet and StarXTerminator is yielding good benefits for the astrophotography community.  Ron Brecher gave a presentation on the Astro Imaging Channel that described how he removes stars from stretched images only.  I opted to for the linear state as the results were essentially the same for StarXTerminator (Starnet2 does a stretch before star removal with linear data).  The other issue I faced was how to integrate the Ha data with the RGB color image.  Recently, Shawn Nielsen did a YouTube video on how he does this with PixelMath using the Ha image as a mask before doing the combination.  The Ha image mask is essential to prevent having a red cast added to the background.

NGC 2403 is a relatively small spiral “flocculent” galaxy in the constellation Camelopardalis.  It is a fairly large and bright target in the northern sky, and it gave me a chance to get a jump on galaxy season.  It is surprising that Charles Messier missed this galaxy with a magnitude of 8.25.  The galaxy is classified as SABc, with a diameter of 60.7 kly at a distance of 10 Mly from Earth (SkySafari Pro 7).  NGC 2403 is rich in gas and dust giving it a “fuzzy” appearance, and it has a large number of bright emission nebulae.

Imaging details:

Celestron 9.25" Edge HD SCT
Celestron 0.7x Focal Reducer (FL = 1645mm, f/7)
Celestron off-axis guider with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10oC)
ZWO 36mm Hydrogen-a, Oxygen-III and Sulfur-II filters
RA: 114.20667, DEC: 65.60798o, Equatorial camera rotation: 0o

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 with StarXTerminator with AI version 8,
    Photoshop CC 2022

Hydrogen-a  10 min x 7 subframes (70 min), Gain 100, Offset 68, 2x2 binning
Luminance   2 min x 97 subframes (194 min), Gain 100, Offset 68, 2x2 binning
Red                4 min x 26 subframes (104 min), Gain 100, Offset 68, 2x2 binning
Green            4 min x 27 subframes (108 min), Gain 100, Offset 68, 2x2 binning
Blue               4 min x 28 subframes (112 min), Gain 100, Offset 68, 2x2 binning