1 - X-ray lines and edges

Summary

The X-ray waveband contains atomic and ionic transitions for nearly all astrophysically abundant elements – with the notable exception of H and He. These arise primarily from transitions involving electrons in the 1s shell but for heavier elements (i.e. Fe, Ni), there are transitions involving higher shells as well. This appendix contains a short discussion of spectroscopic notation combined with information on a selection of particularly strong transitions, including those from hydrogen-like and helium-like ions, Fe XVII–Fe XXIV, as well as fluorescent transitions from neutral atoms and ionization edges for all of the abundant elements. More information about atomic data useful for X-ray astronomy can be found at http://www.atomdb.org.

Spectroscopic notation

A complete discussion of spectroscopic notation is beyond the scope of this handbook; we suggest the short but highly informative text by Herzberg (1945) for a more detailed review; another useful source is the X-ray Data Booklet published by the Center for X-ray Optics and Advanced Light Source at Lawrence Berkeley National Laboratory (http://xdb.lbl.gov). It should be noted that X-ray astronomy is rife with poorly used spectroscopic terminology, so following the form used by an earlier refereed paper does not guarantee proper usage.