2001AJ....122.1538B

We derive some element abundances for the central star of the planetary nebula K648 from analysis of Hubble Space Telescope Faint Object Spectrograph spectra (1200-3300 Å). Carbon is found to be approximately 4 times overabundant with respect to solar values, while oxygen is underabundant and silicon about solar, and He/H=0.6. The stellar continuum indicates a reddening of E(B-V)=0.08 and is well approximated by a synthetic model with T_eff=37,000 K and logg=4.0, as found previously by (ref???)Heber, Dreizler, & Werner. The scaling of the synthetic model with the measured UV flux indicates R=1.3 R_☉, and thus log(L/L_☉)=3.45, M=0.62 M_☉, assuming a distance of D=10.3 kpc. The C IV exhibits a wind profile, from which a terminal wind velocity of V_∞=1600±150 km s^–1 is derived and a column density of N_i(C IV)=6±3x10¹⁵ cm^–2. From ground-based spectra obtained at the William Hershel 4.2 m telescope we derive the first measurement of the expansion velocity for the nebula: V_exp([N II])=11.9 km.s^–1 and V_exp(Hα)=16.7 km.s^–1. Combined with the nebular radius measured from HST imaging in our previous paper, the velocity yields an expansion age of the object Age_kinematic≥4270 yr. This value is slightly higher than predictions from post-AGB evolutionary models for a ~0.6 M_☉ He-burning remnant. The photospheric overabundance of He and C, as well as the low luminosity of the central star, are consistent with a post-AGB object that experienced a late thermal pulse and consequent third dredge-up, and which is now in a luminosity-dip He-burning phase. The progenitor mass is fairly low.