[Fe ii] 8616 Å/[O i] 6300 Å  ratio plotted against the gas temperature for a density of 5 × 10⁴ cm^-3. The solid curve shows predictions assuming an [Fe/O] solar gas phase abundance of 0.062 (Asplund et al. 2006). Other curves are plotted for decreasing values of the [Fe/O] abundance. Data points correspond to the values measured in the HVC and LVC toward HH34 IRS, and indicate an [Fe/O] abundance ratio close to solar for the HVC and a factor between 2 and 8 below solar for the LVC.