and adopting an absorption cross–section per carbon atom of 3 × 10−18 cm−2 (Allamandola et al. 1989) and an interstellar carbon abundance C/H=2.3 × 10−4 (Snow & Witt 1989;
and adopting an absorption cross–section per carbon atom of 3 × 10−18 cm−2 (Allamandola et al. 1989) and an interstellar carbon abundance C/H=2.3 × 10−4 (Snow & Witt 1989;