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J.E. Herald, Luciana Bianchi (Center for Astrophysical Sciences, The Johns Hopkins University)
We present results from a comprehensive spectral analysis of FUSE, IUE, HST and ground-based data of Galactic and LMC Central Stars of Planetary Nebulae (CSPN). We determine the central star parameters and the characteristics of the circumstellar envelope, and discuss their evolutionary implications.
Typically, the spectra of a CSPN in the optical and near-UV range are dominated by its nebula. The wavelength range of FUSE (905-1187Å) discloses the continuum of the hot central star, as well as important diagnostic lines (e.g. O VI 1032,1037) which allow determination of the central star's photospheric and wind parameters. We have determined the stellar parameters with stellar atmosphere codes (TLUSTY and CMFGEN). In some cases, the high resolution of FUSE (~15,000) allows us to determine the characteristics of the H2 gas associated with the nebula as well as the component associated with the ISM.
By determining the present-day characteristics of the central star, and inferring its past through study of its expelled ionized and molecular materials, a more complete picture of the star's evolution is gained, including the mass of the progenitor star. Modeling the central star's spectrum gives its parameters as well as the (unobservable) EUV radiation field, which can be used as input to photoionzation models to constrain parameters of the nebula. This information can be used to test theories of stellar evolution, nebular shell formation, and radiative wind driving.
This study is currently being extended to include CSPN in the LMC (FUSE cycle 2) and the SMC (FUSE cycle 3).
This work has been funded by NASA grant NAG 5-9219 (NRA-99-01-LTSA-029).