Linear polarization of resonance lines in the absence of magnetic fields. I - Slabs of finite optical thickness

Effects of partial frequency redistribution on resonance polarization of spectral lines in the absence of magnetic fields are studied for resonance lines formed in finite slabs. The emphasis is on testing the validity (for polarization calculations) of various approximate forms of the so-called R_II frequency redistribution function which describes the formation of resonance lines formed in dilute media. Polarization profiles obtained with the angle-dependent R_II are compared to profiles calculated with the angle-averaged form of R_II and its approximate versions proposed by Kneer and Ayres. A comparison with complete frequency redistribution polarization profiles is also presented.