Unified NLTE model atmospheres including spherical extension and stellar winds. II - EUV-fluxes and the He II-Zanstra discrepancy in central stars of planetary nebulae

Details Unified NLTE model atmospheres including spherical extension and stellar winds. II - EUV-fluxes and the He II-Zanstra discrepancy in central stars of planetary nebulae Unified NLTE model atmospheres including spherical extension and stellar winds. II - EUV-fluxes and the He II-Zanstra discrepancy in central stars of planetary nebulae

May 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991a%26a...245..587g&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 245, no. 2, May 1991, p. 587-592. Research supported by Max-Planck-Institut fü

Statistics

Computation

38

Planetary Nebulae, Stellar Atmospheres, Stellar Winds, Computational Astrophysics, Stellar Models, Model Atmospheres, Central Stars Of Planetary Nebulae, Stellar Winds

Scientific paper

A large grid of unified NLTE model atmospheres including radiation driven winds and spherical extension is computed for central stars of planetary nebulae (CSPN) in the effective temperature range from 40000 K to 100000 K. The calculated energy distributions are used to investigate the longstanding problem of the "Zanstra-discrepancy". It is shown that the increase of EUV flux in the unified models, caused by the presence of the wind velocity field in the layers of He II groundstate continuum formation leads to much better agreement with the observations than was the case before, when plane- parallel hydrostatic models were used. However, for a significant fraction of the Central Stars investigated (45%) the computed flux is still about 1 dex too small. The remaining discrepancies are attributed to additional EUV-photons generated by shocks in the radiation driven winds. The ad hoc assumption of a blackbody energy distribution for λ < 228 Å using an effective temperature determined from the photo spheric NLTE analysis of hydrogen and helium lines provides an excellent empirical description of the observed EUV flux.

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