Polynomial Approximants for the Calculation of Polarization Profiles in   the \ion{He}{1} 10830 \AA Multiplet
  The \ion{He}{1} multiplet at 10830 \AA is formed in the incomplete Paschen-Back regime for typical conditions found in solar and stellar atmospheres. The positions and strengths of the various components that form the Zeeman structure of this multiplet in the Paschen-Back regime are approximated here by polynomials. The fitting errors are smaller than $\sim10^{-2}$ m\AA in the component positions and $\sim10^{-3}$ in the relative strengths. The approximant polynomials allow for a very fast implementation of the incomplete Paschen-Back regime in numerical codes for the synthesis and inversion of polarization profiles in this important multiplet. 
H. Socas-Navarro, J. Trujillo Bueno & E. Landi Degl'Innocenti