Casitas de Gila, Gila, NM, October 3 - 7, 2023

NGC 869 and 884 are two open star clusters located near each other in the constellation Perseus.  Each cluster consists of new stars born in one or two large clouds of dust and gas.  Once fusion started in the newborn stars, their intense solar wind blew the remaining gas away.  Gravitational interactions between the stars and other matter in the galaxy sent them out of their birthplace.  Based on their individual stars, the clusters are relatively young, both about 14 million years old.  The clusters are approximately about 7,500 light years away and are located in the Perseus Arm of the Milky Way galaxy.  Both clusters are moving towards us at speeds between 38 and 39 km/s as measured by their blueshift.  The double cluster is visible with the naked eye at a dark sky site and is one of the gems of the fall and winter seasons. (Wikipedia, NASA)

Conditions were excellent over several nights at a dark sky site in New Mexico to image the iconic double cluster in the constellation Perseus.  Seeing was average to above average and transparency was mostly above average to excellent.  The double cluster was imaged as a late second target, completing each night before the light of dawn.  Processing in PixInsight was straight forward for the RGB stars image.  Several images on Astrobin showed a HII emission region in the background.  Hydrogen-alpha narrowband filter data were collected to add this to the star cluster.  The Ha master created by the WBPP script in PixInsight was processed and then StarXTerminator was used to remove the stars.  The starless Ha image was denoised aggressively and stretched with a dark background.  Note that the hydrogen emission is very faint in this field.  The stretched and saturated RGB image with the stars was then combined using a simple PixelMath combination to give the final image a hint of the faint red emission in the background.

Note that I tested a new beta version of GraXpert, a gradient removal application that now has an AI based method that worked well on the RGB image.  The waning moon was up when I shot the red, green and blue filter subframes, so there were gradients to be removed, as well as in the Ha data.

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, Sulfur II, Red, Green, and Blue filters
Equatorial camera rotation: 0 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 2023

Hydrogen-a 10 min x 21 subframes (210 min), Gain 100, Offset 32, 1x1 binning
Red             1 min x 95 subframes (95 min), Gain 100, Offset 32, 1x1 binning
Green          1 min x 92 subframes (92 min), Gain 100, Offset 32, 1x1 binning
Blue            1 min x 92 subframes (92 min), Gain 100, Offset 32, 1x1 binning

Total integration time: 8.15 hours