Carbon abundance in the Magellanic Clouds from IUE observations of H II regions

Observations of C II], C III], and C IV lines in the ultraviolet spectra of three H II regions in the Small Magellanic Cloud (SMC) and of four H II regions in the Large Magellanic Cloud (LMC) were obtained with the International Ultraviolet Explorer satellite and used to derive the carbon abundance in the Megellanic Clouds by nebular model analyses. Based on absolute emission line fluxes between the IUE and ground-based observations for the individual H II regions, it is found that 12+log C/H = 7.16 +- 0.04 for the SMC and 7.90 +- 0.15 for the LMC (where the errors quoted are statistical; systematic errors due to aperture geometry and positioning differences between the IUE and ground-based observations may be several times larger). The corresponding values for the average C/O ratios are log C/O = -0.89 +- 0.02 for the SMC and -0.48 +- 0.04 for the LMC (statistical errors). For one SMC H II region, N81, the O III] lambda1663 lines were observed in the IUE spectra and permitted direct calculation of the C/O ratio independent of absolute fluxes. The result (log C/O = -0.94) is in excellent agreement with ratio based on absolute fluxes