IMAGE CONTENTS

I have been thoroughly enjoying Annals of the Deep Sky by Jeff Kanipe and Dennis Webb. Volume 4 includes Cassiopeia with several pages devoted to the Heart and Soul Nebulae. Much of the following information is gleaned from there.

This is IC1848, commonly called the Soul Nebula, in Cassiopeia rendered in the SHO palette using narrow band (NB) Ha, SII, OIII data. Referring to the annotated image (Rev E) the larger nebula region is marked as Sh2-199, and the star cluster mid-right in the center of the large right lobe is IC1848. The small nebula regions to the left and lower right of the main body are Sh2-201 and Sh2-198, respectively. The fuller region shown is also Westerhout 5 (W5).

This is a HII region being ionized by star cluster IC1848, comprised mostly of OB stars. The distance is on the order of 1.9 to 2.4 kpc. And now a little bit from Wikipedia. There are large cavities present that were carved out by radiation and winds from the more massive stars. The theory of triggered star formation is that this action pushes gas together causing the ignition of a new generation of stars. Scientists have shown that the ages of the stars here become progressively younger further from the center of the cavities.

I have also annotated the magnitudes of the brighter stars down to magnitude 10. Although they appear quite bright and prominent in this image, none of them are named and are most likely not visible to the naked eye even from a dark site.

My annotation search also yielded 3 PGC galaxies, two of which remarkably can be seen through the main body of the nebula, but I did not include them here as they are not visible in this NB image. Most likely they are too far away and red shifted out of the 3nm Ha filter band.

ACQUISITION & PROCESSING NOTES

This nebula is framed very nicely with the Tak FSQ-106EDX4 and FLI ML16200 at 2.332 arcsec/px. The Ha data was taken during earlier sessions starting in late October. The SII and OIII data was taken more recently in mid November. The later is, as usual, weaker data in more need of tender care to eek out detail in those channels.

NB color processing is very much a matter of taste, and it's been my more recent goal to show as much distinction as possible of the three-wavelengths information in my data. Typically, as seen here, it is difficult for me to find regions of more distinct separation of SII from the Ha. These are the various brown and yellow areas. OIII shows up more prominently in the central areas of the nebula. The green color is most dominant from the strong Ha signal, which had to be suppressed relative to the other two channels in order to bring out the contrast seen here.

It is my ongoing intention to reduce the amount of processing in my images, particularly those taken at this wide FOV scale. I like to see what the data and integration time can do for the quality and detail of the image. Even so, I did apply noise reduction at the linear and nonlinear stages, although I did scale back the amount quite a bit from past processing. In fact in my first pass with this data I used my usual heavy hand, and in the end I got a creamy, unnatural result that does not fit my taste. Unlike what I used to believe, noise is not inherently bad, and too much noise reduction can smooth out detail and naturalness.

Another thing I did not apply here was a late processing sharpening step. This can, when not applied with a heavy hand, sharpen up some of the nebula detail, but I have never liked what it does to the stars. The stars often become so sharpened that they look like little flat white discs with no smooth transition between star and background. Even star masking has never satisfactorily work for me except at much smaller image scales. So, no sharpening was done here. (Besides, if you soak in the image as a whole, you would barely even notice the sharpening anyway.)

CONCLUSION

I hope you enjoy this image. I have a previous image of nearby IC1805, the Heart Nebula, and I am going to see to what extent the two images overlap and could be built up into a mosaic, at least the Ha data.