ANALYSIS OF VOYAGER SPECTRA OF THE BETA-CEPHEI STAR NU-ERIDANI

Voyager 500-1700 angstrom spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observatio ns were obtained in 1981 and cover six pulsation cycles of the star. T hese data are supplemented with a set of nine IUE SWP high-resolution observations covering one, earlier epoch, pulsation cycle. Light curve s are derived from the Voyager data at 1055 and 1425 angstrom. These l ight curves are found to be consistent in both shape and period with p ublished optical curves. The 1055 angstrom light curve also exhibits a phenomenon not seen in the optical curves: a small but highly signifi cant systematic increase in the flux of the maximum light phases while maintaining a constant minimum light level over the interval of obser vation. Substantially larger errors in the longer wavelength data prec lude discussion of this phenomenon in the 1425 angstrom light curve. E xamination of the far-UV continuum in v Eri during this period shows t hat the color temperature is lower for the brighter maxima. Analysis o f the far-UV continuum at maximum and minimum light yields an effectiv e temperature difference between these two phases of 2200 +/- 750 K. S pectroscopically, three prominent features are seen in the Voyager dat a: a feature at 985 angstrom mostly due to a blend of C III 977 angstr om, H I Lygamma 972 angstrom, and N III 990 angstrom; a feature at 103 0 angstrom due to H I Lybeta 1026 angstrom and C II 1037 angstrom; and the Si IV resonance doublet near 1400 angstrom. A comparison of the 9 12-1700 angstrom spectral region in v Eri with a set of standard, i.e. , nonpulsating stars, shows that nu Eri closely resembles the standard both in continuum shape and spectral line strengths with the possible exception of a slight flux excess between 912 and 975 angstrom. The e quivalent width of the 985 angstrom feature is shown to vary in streng th over the pulsation cycle in antiphase with the light curve and vari ations seen in the C iv 1548-1551 lines from the IUE data. This behavi or of the 985 angstrom feature is most likely caused by variations in the strength of the Lygamma component of the blend. Comparisons are al so made between nu Eri and the only other beta Cephei star studied in the far-UV, BW Vul, with the most notable differences between the two stars being the much larger DELTAT(eff) for BW Vul and the almost tota l absence of abnormalities in observed spectrum of nu Eri.