We analyze the Far-UV/UV spectra of four central stars of planetary nebulae with strong wind features — NGC 2371 , Abell 78 , IC 4776 and NGC 1535 , and derive their photospheric and wind parameters by modeling high-resolution FUSE ( Far-Ultraviolet Spectroscopic Explorer ) data in the Far-UV and HST-STIS and IUE data in the UV with spherical non-LTE line-blanketed model atmospheres .
Abell 78 is a hydrogen-deficient transitional [ WR ] -PG 1159 object , and we find NGC 2371 to be in the same stage , both migrating from the constant-luminosity phase to the white dwarf cooling sequence with \mbox { $T _ { eff } $ } \simeq 120 kK , \mbox { $ \dot { M } $ } \simeq 5 \mbox { $ x 10 ^ { -8 } $ } { M _ { \odot } \ > yr ^ { -1 } } .
NGC 1535 is a “ hydrogen-rich ” O ( H ) CSPN , and the exact nature of IC 4776 is ambiguous , although it appears to be helium burning .
Both objects lie on the constant-luminosity branch of post-AGB evolution and have \mbox { $T _ { eff } $ } \simeq 65 kK , \mbox { $ \dot { M } $ } \simeq 1 \mbox { $ x 10 ^ { -8 } $ } .
Thus , both the H-rich and H-deficient channels of PN evolution are represented in our sample .
We also investigate the effects of including higher ionization stages of iron ( up to Fe x ) in the model atmosphere calculations of these hot objects ( usually neglected in previous analyses ) , and find iron to be a useful diagnostic of the stellar parameters in some cases .
The Far-UV spectra of all four objects show evidence of hot ( T \sim 300 K ) molecular hydrogen in their circumstellar environments .