NGC 3293: HORGB versus HO Lines--Why do they appear different?

OTA: CDK 24
Camera: Moravian 61000
Observatory: Heaven's Mirror
Date of Capture: May '24
Date of Processing: May '24

Exposures Used:
R: 13 x 300 sec
G: 13 x  "
B: 13 x  "
L:  x  "
H: 12 x 900 sec Gain 3x
O: 12 x   "
Total Exposure time: 7.3 hours
Image Width: 31' 10"

Processing Tools:
1.    Commercial: PixInsight, Topaz, Radiant Photo, PhotoDirector
2.    Pixinsight Addons: NoiseXTerminator, BlurXTerminator, StarXTerminator
3.    My Scripts: NB_Assistant, AC_Restar, Subframe Weighting Tool (Excel w/ J. Hunt), ColorTweaker

Discussion:
The designation NGC 3293 refers to the open cluster of stars, not the nebulae (as is often the case). The stars in this cluster are relatively young, about  12M years old.

The two images I posted are of the same target by recorded/processed in two commonly used modes: one with only the narrowband data (Ha and OIII) in this case, and the other a combination of the narrowband and the broadband data (Ha, OIII, Red, Blue, and Green). Some interesting differences occur between these two representations.

First, you can change from one image to the other by a "mouseover." The HO image is the base image, and the HORGB displays when the mouse hovers over the image. The stars in both images are from an RGB image.

Perhaps the most obvious difference is the presence of the blue reflection in the HORGB image and its absence from the HO image. The reflection nebula arises from the scattering of starlight by gases and molecules, not by emissions from excited atoms, such as Ha and OIII. Therefore, the Ha and OIII filters, which allow only those emission wavelengths to reach the camera sensor, do not pick up much of the scattered blue…but probably a little of it is passed by the OIII filter, but not enough to make much of an impact.

Also note that the other nebulae, such as the red and other-colored nebula not reflecting the light from the star cluster, appear with more detail in the HO image than in the HORGB image. This is because the RGB filters allow virtually all wavelengths from any source through to the camera sensor. Vibrating molecules and a plethora of sources emit a continuum of radiation in all colors from all regions of the nebula. This radiation background washes out details that separate one region's emissions from another. A worse still, color-resolution degrading effect is introduced by using data captured through a luminance filter, which does not even separate R from G from B and no less the emissions from the background. (This data set did not include luminance subframes, which have their place, too, but not where the imaged region is differentiating chemistry and processes by color/color contrasts.)

Processing Description:
Just briefly, the H and O lines were extracted from the background radiation using NB_Assistant, which solves sets of simultaneous equations that relate the broadband and narrowband contributions to the values of each image pixel. This separation allows even greater isolation of details in areas lit by emission lines.

Target Statistics:
Distance: 8.4k ly
Pixel Resolution: 0.39"
Pixel Span at Target: 1.5E10km
Image Width 1.4E14 k

Alex Woronow