It is interesting - as far as one is able - to delve into the science that determines the particular colours and forms of the various planetary, emission, supernova remnant and other types of nebula. I got puzzled over questions like - for example - why when sulfur is such a relatively minor constituent of star stuff do we use the Hubble palette - what does SII tell us and what unique scientific insight does it provide ? What is OIII, how is it excited to produce light and why is it's light dominant over HA in planetary nebula but usually, if at all, only more faintly found near the core of HA emission nebulae ? Why does SII signal show up at the edges of HA in emission nebulae ? Why can there be more SII in supernova remnants etc etc
So in case possibly interesting or useful to anyone else - below are a rather eclectic set of links to a few articles that I personally found interesting and also reasonably accessible (i.e. meaning I was happy to understand just 20% of them or even just 2% of the last two
) as start points for gaining some understanding about quite why nebulae look as they do along with their consitituent atomic abundances. The reading also provided just a flavour of some of the debates that remain topical in nebula science - for example whereas the physics of recombination line spectroscopy (e.g. such as HA line generation from ionized H) and of collisionally excited forbidden line spectroscopy (e.g blue/ green line generation from OIII) are both well understood the two types of spectroscopy nevertheless produce quite different estimates of the temperatures and densities of nebulae; no doubt astrophysicists will eventually gain new understanding about nebula structure from the resolution of this disagreement.https://wikis.uit.tufts.edu/confluence/ ... ?version=1
https://star.pst.qub.ac.uk/webdav/publi ... ub2015.pdf
https://clarkvision.com/articles/index.html
https://iopscience.iop.org/article/10.1 ... 873/aa72c3
https://www.stsci.edu/~volk/pnspectra.html
https://ned.ipac.caltech.edu/level5/Mar ... rames.html
http://www.astronomy.ohio-state.edu/~po ... onized.pdf
Tim
