Physical conditions of nebulae/HII regions

[faeriewhisper]

Hello to all!
I'm trying to develop a routine (in ESO-MIDAS) similar to NEAT (Nebular Empirical Analysis Tool) or NEBULAR package from IRAF that, by inputting certain emission line ratios i could get the physical conditions of the nebula (like Te, Ne, ionic and elemental abundances).
The thing is, since i don't have any education of atomic physics, I'm finding big problems to understand this.
I've read a lot, but i still cannot understand simple stuff like, how to determine if the nebula is low, medium or highly ionized, and how to use the atomic data to get temperatures and densities.

So please, if you are a expert in this area, i would be very appreciated if you could explain to me how this works.

Thanks in advance.
Kind regards, Iris.

 

[AndyW]

Hello Iris,

Thank you for reaching out and expressing your interest in developing a routine similar to NEAT or NEBULAR. As a scientist with a background in atomic physics, I would be happy to explain some basics to you.

Firstly, to determine if a nebula is low, medium, or highly ionized, we need to look at the emission line ratios. These ratios can tell us about the ionization state of the gas and the physical conditions of the nebula. For example, a highly ionized nebula will have a higher ratio of highly ionized lines (e.g. [O III], [Ne III]) to lowly ionized lines (e.g. [O II], [S II]) compared to a lowly ionized nebula.

To use atomic data to get temperatures and densities, we need to use the concept of ionization equilibrium. This means that the rate of ionization of an atom must be equal to the rate of recombination of the ion. By studying the emission line ratios of different ions of the same element, we can determine the temperature and density of the gas.

To do this, we use the atomic data for each ion, which includes the energy levels and transition probabilities. These can be found in databases such as the National Institute of Standards and Technology (NIST) Atomic Spectra Database. By comparing the observed emission line ratios to the predicted ratios based on this atomic data, we can determine the physical conditions of the nebula.

I hope this explanation helps you understand the basics of using atomic data to determine physical conditions of a nebula. I would recommend further reading and studying on the topic to gain a deeper understanding. Best of luck with your routine development!