The IUE Spectrum of the "O VI Sequence" Planetary Nebula He 2-55

Abstract

The first IUE observations of the "O VI Sequence" planetary nebula He 2-55 are reported. The ultraviolet spectrum is dominated by strong emission lines of O V, C IV, He II, and C III], plus a number of weaker ions for which emission line fluxes were measured. N V lambda 1240 and C IV lambda 1549 show P Cygni profiles. The stellar terminal wind velocity of 4500 +/- 400 km s-1 is derived from the C IV lambda 1549 absorption. Interstellar extinction, E(B - V) = 0.54 +/- 0.1, was determined from the observed flux of the He II lambda 1640/ lambda 4686 lines. The only density diagnostic available from low-dispersion data, the Si III]/C III] emission-line ratio, yields an electron density of log Ne = 9.5 +/- 0.5 cm-3 but usually results in higher log Ne than that derived from the C III] F( lambda 1907/ lambda 1909) diagnostic that requires high-dispersion data.