Chemical abundances

iSpec implements two approaches to derive individual chemical abundances: the synthetic spectral fitting technique and the equivalent width method.

Synthetic spectral fitting technique

The process is equivalent to the determination of atmospheric parameters with this technique and the same menu option should be selected "Parameters - Determine astrophysical parameters with synthesis". It requires:

• Atmospheric parameters
• Fix all the parameters except the "individual abundance" and select the element to be derived
• Line masks corresponding a lines of the element we want to derive
• Segments that cover one or more line masks and for which the synthetic spectra will be computed (instead of the full spectrum, which would be slower)

The results are shown directly in the terminal.

Equivalent width method

Again, the process is similar to the determination of atmospheric parameters with equivalent width but the menu option is "Parameters - Determine abundances with equivalent widths". The following steps are needed before the determination:

• Load a spectrum and the line masks to be used in the analysis
• Fit the continuum
• Fit the lines:
  • A gaussian/voigt profile will be fitted to determine the equivalent width, central wavelength, etc.
  • A cross-match with the some selected atomic data will be executed to assign atomic data for each line (it will be used to derive atmospheric parameters)
• Specify the atmospheric parameters of the star