Line ratios of HH sources with “low-” (open circles), “intermediate-” (filled circles) and “high-excitation” (crosses) spectra (data and definitions adopted from Raga et al. 1996). Red symbols represent the brightest knots in HH 1042 (knot E) and HH 1043 (knot B). The shaded region denotates the ratios predicted by the plane-parallel shock and bow-shock models in Hartigan et al. (1987). The high excitation in HH 1042 and HH 1043 can be explained by photoionization and/or -excitation by an external source of radiation.
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