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R.C. Iping (Catholic University of America), G. Sonneborn (NASA/GSFC)
P-Cygni, AG Carinae, S-Doradus and Eta Carinae were observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. FUSE covers the spectral range 905 to 1187 Angstroms at a resolution of 0.05 Angstroms. In this paper we explore in what way the LBV's are similar and in what way they are different. For Eta Car the observed flux at 1160 A, is 4E-12 erg/cm2/s/A. This is 20X larger than observed by STIS/E140M at the same wavelength through a 0.2"x0.2" aperture. The flux level declines toward the Lyman limit where converging molecular and atomic hydrogen features completely blanket the spectrum. The shape of the spectrum shortward of 1110 Angstroms is dominated by strong absorption bands of interstellar molecular hydrogen. In addition to many strong interstellar atomic species, the spectrum contains several prominent P-Cygni features, including C III 1175, S IV 1063-73, Si III 1113, and N I 1134. The lines are broad with unsaturated absorption troughs, implying that the wind is patchy and/or only partly covers the UV emitting surface. The wind absorption extends to -1000 km/s. The large far ultraviolet flux levels at 1150-1180 A, relative to those observed by HST/STIS, imply that the observed far-UV spectrum is formed in an extended ~ 1-2 arcsec diameter UV scattering envelope. The far-UV spectra of P Cygni and AG Carinae are very similar and indicate a cooler atmosphere than Eta Car and S Dor. There is very good agreement between the FUSE spectrum of P Cygni and a model atmosphere computed by Hillier with his code CMFGEN.
This work has been supported in part by NASA grants NAG5-8631 to Catholic University of America and NAS5-32985 to Johns Hopkins University.