... stars

Appendix is only available in electronic form at http://www.edpsciences.org

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... carbon

Snow & Witt (1995) discussed the carbon abundance in stars newly formed from the ISM and conclude that the carbon abundance in the local ISM is ( $2.24\pm0.5)\times 10^{-4}$.

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... Table 1

To fit the observed IR spectrum of the diffuse ISM, Li & Draine (2001a) include enhancement factors E_6.2, E_7.7 and E_8.6 in the integrated cross sections for the 6.2, 7.7 and 8.6 $\mu$m bands. For the template model, we adopt E_6.2, E_7.7, E_8.6 equal to 1, which recover typical laboratory values, but we will also consider the model with E_6.2, E_7.7, E_8.6>1 (see Sect. 4.2.5).

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... estimate

To estimate $\gamma$, we take $\gamma _0 \sim 3 \times 10^{-6}$ and $f(N_{\rm C})\sim 11$ as in Bakes & Tielens (1994).

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...

In Fig. 9, the data for the embedded young stellar object WL 16 have been corrected for dust attenuation taking a visual extinction of $A_{\rm V}=31$from Ressler & Barsony (2003) and using the extinction coefficient of Draine (1989); Draine & Lee (1984).

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