Including nine stars from Orion (NS11), in units of log (El/H) + 12 / atoms per 10⁶ H nuclei – computed from average star abundances (mean values over all individual lines per element, equal weight per line), the uncertainty is the standard deviation;

Esteban et al. (2004);

Simón-Díaz & Stasińska (2011);

difference between the cosmic standard and Orion nebula gas-phase abundances, in units of atoms per 10⁶ H nuclei;

Sofia & Meyer (2001);

value determined from strong-line transitions (Sofia et al. 2011), which is compatible with data from the analysis of the [C ii] 158 μm emission (Dwek et al. 1997). Weak-line studies of C ii] λ2325 Å indicate a higher gas-phase abundance ε(C) = 8.11 ± 0.07 (Sofia 2004), which corresponds to 84 ± 28 ppm of carbon locked up in dust;

Meyer et al. (1997), corrected accordingly to Jensen et al. (2007);

Cartledge et al. (2004);

Cartledge et al. (2006). The uncertainty in the ISM gas-phase abundances is the standard error of the mean;

difference between the cosmic standard and ISM gas-phase abundances, in units of atoms per 10⁶ H nuclei;

photospheric values of Grevesse & Sauval (1998, GS98), Asplund et al. (2009, AGSS09) and Caffau et al. (2010, CLSFG10).