Resonance line transfer with partial redistribution. V. The solar Ca II lines

Line profiles for the Caii H and K lines have been calculated, accounting for the partial frequency coherence of scattered photons. These profiles are compared with calculations made with identical atomic and atmospheric models but assuming complete redistribution. Very significant differences between the profiles obtained using these two different physical descriptions of the scattering process are found, and it is now apparent that the assumption of complete redistribution is a serious oversimplification of the actual physical situation. The partial redistribution (PRD) results are in substantially better agreement with observation than the complete redistribution (CRD) profiles in describing (a) the center-to-limb behavior of the intensity at K₁ and K₂, (b) the center-to-limb behavior of the wavelength positions of K₁ and K₂, and (c) the relative behavior of the H and K profiles, as a function of wavelength, at disk center. Further, we find that we may match the observed absolute intensity at K₁ with a minimum chromospheric electron temperature of about 4450 K, and that HSRA temperature minimum is too low when partial redistribution effects are taken into account. This result raises questions about the validity of equating brightness temperatures observed at K₁ in stellar spectra with minimum temperatures in stellar chromospheres; it appears likely that such a procedure will systematically underestimate the value of T). (authors)