This tutorial explains the procedure used to analyze an optical emission-line spectrum produced by a nebula ionized by massive star formation. Particularly, the methodology used to derive physical properties, such as electron density and temperature, and the ionic abundances of the most representative elements whose emission lines are present in the optical spectrum is described. The main focus is on the direct method, which is based on the measurement of the electron temperature to derive the abundances, given that the ionization and thermal equilibrium of the ionized gas is dominated by the metallicity. The ionization correction factors used to obtain total abundances from the abundances of some of their ions are also given. Finally, some strong-line methods to derive abundances are described. Such methods are used when no estimation of the temperature can be derived, but which can be consistent with the direct method if they are empirically calibrated.
Publications of the Astronomical Society of the Pacific
- Pub Date:
- April 2017
- Astrophysics - Astrophysics of Galaxies
- 27 pages, 9 figures. Accepted for publication as invited tutorial in PASP. Equation (3.5) relating t(OII) with RO2 corrected. Equation (4.20) for Ne2+ corrected. Some coefs. of the extinction law have been corrected