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Astron. Astrophys. 322, 73-85 (1997)

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Appendix A: Mappings Ic

The multipurpose shock/photoionization code MAPPINGS was developed at Mount Stromlo Observatory (see Binette et al. 1985) and has since been maintained and transformed independently over the years by two independent groups. This has lead to very different versions: the branch MAPPINGS I which is maintained by Luc BINETTE (LB) and MAPPINGS II which is maintained by Ralph SUTHERLAND (RS). The two codes share many of the initial routines (e.g. the time-dependent ionization balance algorithm) although, in the most recent versions the transfer of the resonance lines and the dust effects have been developed independently by LB and RS. Moreover, RS has rewritten completely the shock model for his version II (see Sutherland 1993; Sutherland & Dopita 1993; Dopita & Sutherland 1996). One practical advantage of upgrading two codes independently is that the results can at any time be compared to test for possible errors in the implementation of new applications or physical effects or in the updating of atomic physics.

We now proceed to describe the most recent version developped by LB: MAPPINGS IC which is used in deriving the results on bowshock models presented in this paper. The limitation in LB's version I of a maximum of 6 ionization stages has been removed. The version MAPPINGS IC computes the ionization balance over up to 26 ionization stages if or when necessary. However, in any point of a photoionized nebula or of a collisionally ionized gas stream, the ionization stages are calculated in a narrower (but moveable) window of ionization stages: 14 stages in the equilibrium ionization case (e.g. photoionized nebulae) and from 8 to 12 stages in the time-dependent ionization case (e.g. interstellar shocks). The window's position in terms of which ions' abundances are calculated, is determined iteratively and made to cover the most abundant ionic species of each element. MAPPINGS IC now includes iron. All these changes were greatly simplified by the use of the data files compiled by RS for his version II. The collisional ionization coefficients are from Arnaud & Rothenflug (1985). We adopt the collisional excitation rates of hydrogen calculated by Aggarwal et al. (1989).

The treatment of dust effects in MAPPINGS IC (dust scattering, line transfer, photoheating, depletion) remains as defined in version I (Binette et al. 1993a, 1993b). Most forbidden line determination are based on a 5-level system except for [O III ] and [N II ] which use a 6-level structure and [Fe VII ] which use a 9-level structure. When the plasma is very hot, the very high ionization lines in the far UV play a major role in determining the cooling function. To compute the effect of those, we included up to 900 lines as tabulated by Landini & Monsignori (1990) (see also Mewe 1985 and references therein). We suspect that the resonance doublet lines in Landini & Monsignori (1990) for [C IV ], O VI and N V were not divided by the statistical weight of the ground level. This could explain their cooling being twice as large than ours in the range [FORMULA] K.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998