QUANTITATIVE-ANALYSIS OF THE FUV, UV AND OPTICAL-SPECTRUM OF THE O3 STAR HD 93129A

A quantitative analysis of the extremely hot and massive galactic O3 I f supergiant HD 93129A is carried out using stellar wind and pseudo p hotospheric lines observed in the FUV, UV and optical spectrum togethe r with hydrodynamical NLTE model atmospheres. The analysis in the FUV is combined with spectrum synthesis of the molecular and atomic/ionic interstellar spectrum to disentangle stellar and interstellar blends. It is demonstrated that the combined stellar/interstellar spectrum syn thesis technique is crucial for the determination of both interstellar column densities and stellar properties. The fraction of hydrogen ato ms in molecular form in the Carina interstellar clouds is found to be 0.1, smaller than one would expect for its E(B-V) value of 0.54. We at tribute this to dissociation by the strong FUV radiation field of HD 9 3129A. The excitation temperature of ortho-hydrogen (J=1) is about 80K , whereas the excitation to higher levels requires temperatures up to 230 K in accordance with NLTE effects for interstellar H-2 as discusse d in the literature. The abundance of HD relative to H-2 is Of the ord er of 10(-5). For CO we obtain an upper limit of 2.6 x 10(-5). Abundan ces for the interstellar atomic and ionic species are also derived. Th e terminal velocity of the stellar wind of HD 93129A is 3200 +/- 200 k m/s and the rate of mass-loss is 18 x 10(-6) M./yr. The ionization equ ilibrium of the optical emission and P-Cygni lines of N III, N IV and N V is used to determine the effective temperature as T-eff=52000 +/- 1000 K in reasonable agreement with previous values obtained from the helium ionization equilibrium. This high temperature is confirmed inde pendently by an analysis of the Ar VI/Ar VII ionization equilibrium in the FUV. The luminosity of HD 93129A is log L/L.=6.4 +/- 0.1 correspo nding to a zero age main sequence mass of slightly in excess of 120 M. . This very high mass is consistent with the mass determined from the stellar gravity and with the mass derived from V-infinity using the th eory of radiation driven winds. HD 93129A is thus the most luminous an d most massive star known in our galaxy. The abundance determinations yield clear evidence of contamination with CNO-cycled matter in the at mosphere. The abundances of heavier elements are about solar. The pres ence of high ionization stages such as O VI can be explained by X-ray emission due to stellar wind shocks of low temperature (2.5 x 10(6) K) corresponding to the jump velocity of 500 km/s obtained from UV and F UV P-Cygni profiles. Their luminosity is 1.6 dex smaller than the lumi nosity of the high temperature shocks (1.1 x 10(7) K) observed directl y with the ROSAT PSPC. Using effective temperature, gravity, radius an d abundances as input parameters we calculate radiation driven wind mo dels for HD 93129A. We find that the theory is able to reproduce the e xtreme stellar wind properties very precisely.