SH2-170 the Little Rosette Nebula in Cassiopeia

Gold Canyon, AZ
October 29 – November 4, 2021

I imaged this object as the second target of two in Gold Canyon Arizona.  This was the first test of my Losmandy G11 mount using a Periodic Error Correction curve generated with the PEMPro application.  Guiding was improved with an average RMS (standard deviation) error in PHD2 between 0.4 and 0.6 arcseconds.  RMS error was highly dependent on environmental conditions, especially seeing.  I collected a large number of Hydrogen narrowband filter subframes and about 2 ½ hours for each Red, Green and Blue filter.  The best 60% to 70% of the subframes were selected using PixInsight’s SubframeSelector process tool.  I also used the new GradientScaleNormalization script, which worked very well as the scope tracked from reasonably dark skies in the east to light polluted skies in the west toward Mesa.  I tried an evaluation copy of Russ Croman’s StarXTerminator tool in PixInsight to remove the stars from the Ha integrated image to create luminance images for the emission nebula and the stars.  StarXTerminator worked exceedingly well on the Ha image in the linear state.  Starless and stars luminance images were processed separately, and then were recombined to create a stretched, denoised and sharpened master luminance image.  The Ha starless image was combined with the Red integrated image, which was then combined with the Green and Blue integrated images to create a RGB color image.  The RGB color image was color corrected with PixInsight’s PhotometricColorCalibration process tool.  The master luminance image was then combined with the RGB image and processed further to produce the final image with the nebulosity glowing red.

SH2-170, the Little Rosette nebula, is a rather faint hydrogen emission region in the plane of the Milky Way in the constellation Cassiopeia.  It contains a small cluster of young stars in the center.  It is found in the Perseus arm of the galaxy, and it is about 7500 light years from Earth (Ron Brecher).
Imaging details:

Celestron 9.25" Edge HD SCTCelestron 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, Red, Green and Blue filters
RA: 0.35244, DEC: 64.64673, Equatorial camera rotation: 340 deg
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 1.8.8-10 with StarXTerminator,
Photoshop CC 2022

Hydrogen-a 10 min x 40 subframes (400 min), Gain 100, Offset 68, 1x1 binning
Red             2 min x 68 subframes (136 min), Gain 100, Offset 68, 1x1 binning
Green          2 min x 60 subframes (120 min), Gain 100, Offset 68, 1x1 binning
Blue      2 min x 73 subframes (146 min), Gain 100, Offset 68, 1x1 binning