one. According to [@har04], they also yield extinction more consistent with optical spectroscopic result for a protostellar jet.

The ratios of the other three lines, e.g., 1.534 , 1.600 , and 1.664 , to 1.644 are good indicators of electron density [e.g., @oli90]. We solved the rate equation using the atomic parameters assembled by CLOUDY [version C05.05, @fer98] which adopts the Einstein A coefficients of [@qui96] and collision strengths of [@pad93] and [@zha95]. We have included 16 levels which is enough at temperatures of our interest ($\simlt 10^4$ K). We consider only the collisions with electrons, neglecting those with atomic hydrogen, even if the degree of ionization of the emitting region could be low (see § 4.2). This should be acceptable since the rate coefficients for atomic hydrogen collisions are more than two orders of magnitude smaller than those for electron collisions [@hol89]. The ratios of 1.534  and 1.664  lines yield consistent results, e.g., $6,000\pm 400$ cm$^{-3}$ and $5,900\pm 400$ cm$^{-3}$, while 1.600  line ratio yields a little higher density ($7,800\pm 400$ cm$^{-3}$) at $T=5,000$ K which is the mean temperature estimated for line-emitting regions in other SNRs [@gra87; @oli89; see also § 4.2]. The result is not sensitive to 