CG 38, 31, 30, … : The Destiny of Planetary Globules

OTA: CDK24
Camera: Morovian 61000Pro
Observatory: Heaven's Mirror
Date of Capture: Feb '24
Date of Processing: Mar '24

Exposures Used:
R: 16 x 900 sec
G: 26 x  "
B: 16 x  "
L:  provided but degraded resolution captured in the Ha
H: 18 x 1200 sec
Total Exposure time: xxx hours
Image Width: xxx arc-minutes

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

Target Description:
What is happening here is the violent collision of two nebulae and the formation of a shock front that is ionizing the clouds along that front. The dark nebulae are often called "cometary globules" (CG). However, there is nothing cometary about them beyond their shape. These globules are moving rapidly through the background nebula. However, who is moving and who is stationary (or relatively stationary) is not evident without some additional information not present in the image.

This quote from (Kim and Walter, 2005) explains more about the dynamics of these globules, how they evaporate over time, and why they have the shapes they do (see their article for the references):

"The CG formation scenario was discussed by Bertoldi & McKee (1990). Lefloch & Lazaref (1994) imply that these small globules in H II regions are evaporating and being compressed due to the external ionizing sources. Theoretical studies involving "rocket effects" and the "radiation driven implosion" models (Oort & Spitzer 1955; Reipurth 1983; Lefloch & Lazaref 1994) explain how a shock can drive into a spherical clump, compress it, and produce the cometary shape of clouds in pressure equilibrium with surrounding photoevaporating gas. The globule then can be accelerated away from the UV source as it photoevaporates."

As for globule identifications, the small one at the bottom left is CG38. The next one to its right is CG 30, and the large one to the right of that is CG 31. I did not attempt to uncover the names of the remaining globules.

The effects of the erosion are revealed at the tip of CG 30 (and other globules).

Processing Description:
The Ha stack shows far greater detail than the RGB and the L. To exploit this Ha detail, I made an R sub heavily weighted toward the Ha relative to the R and used that to make an RGB image. Attempts not to waste the L were unsuccessful, as even the best way to introduce the L degraded the detail gained from using the Ha in the stated way. L is universally not helpful for detail when the RGB (and/or SHO) are adequate in number and not more binned than the L.

Alex Woronow