Casitas de Gila, Gila, New Mexico, October 25-28, 2022

M33 was the first of two targets imaged over several nights.  I captured narrowband Hydrogen-alpha filter data for the emission regions, and Luminance, Red, Green and Blue broadband subframes for the stars.

In post processing with PixInsight, I used the calibrated and integrated red, green and blue master images for the stars.  The stars image was denoised, stretched and saturated.  The rest of the image processing workflow was made easier with starless images.  As with most of my galaxy processing, getting the RGB colors “correct” was a challenge.  The result of adding Ha to the red channel of the RGB color image was adequate, but took a few iterations of parameter adjustments, i.e., how much Ha to add to the Red.  This, in turn, caused the color of the galaxy core to shift towards the red.  The luminance was a bit odd in that the core region was sharp with good detail, but the arms were “fuzzy”.  StarXTerminator does remove some fine details from the starless image, thinking that they are stars.  However, when the stars image is combined with the starless galaxy, those details are restored.  The stretched, sharpened and saturated starless galaxy was combined with the stars using the PixelMath combine function with the opscreen() parameter.

M33 is a spiral of type SA(s)cd in the small constellation Triangulum. It is about 2.7 million light-years from Earth, the second closest spiral to us,  and it has a diameter of 61,100 light-years.   Thus, it is a small galaxy when compared to the Milky Way or Andromeda, M31.  M33 is a part of the Local Group of galaxies that are gravitationally bound to one another, which includes the Milky Way galaxy and M31.  Triangulum is odd in that it sits by itself without any satellites or nearby dwarf galaxies, yet it is flush with gas and dust and has many star forming regions as shown by the large number of emission nebulae.  While M33 is gravitationally bound to M31, it is not known if it will merge with M31 in the distant future or do a fly-by.  M33 is linked to M31 by several streams of neutral hydrogen and stars, which suggests that a past interaction between these two galaxies took place from 2 to 8 billion years ago. (Wikipedia).

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:  5nm Hydrogen-alpha, 3nm Oxygen-III, 3nm Sulfur-II, Luminance, Red, Green, and Blue
Equatorial camera rotation: 0deg

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 (AI version 10) and NoiseXTerminator,
    Photoshop CC 2022

Hydrogen-a    10 min x 20 subframes (200 min), Gain 100, Offset 68, 1x1 binning
Luminance     2 min x 173 subframes (346 min), Gain 100, Offset 68, 1x1 binning
Red        4 min x 22 subframes (88 min), Gain 100, Offset 68, 1x1 binning
Green    4 min x 22 subframes (88 min), Gain 100, Offset 68, 1x1 binning
Blue       4 min x 22 subframes (88 min), Gain 100, Offset 68, 1x1 binning

Total integration time: 13.5 hours