Synthetic Spectral Analysis of the Hot Component in the S-Type Symbiotic Variable EG Andromeda

Details Synthetic Spectral Analysis of the Hot Component in the S-Type Symbiotic Variable EG Andromeda Synthetic Spectral Analysis of the Hot Component in the S-Type Symbiotic Variable EG Andromeda

2004-07-26

arxiv.org/abs/astro-ph/0407536v1

Astronomy and Astrophysics

Astrophysics

AJ, Oct. 2004

Scientific paper

10.1086/423700

We have applied grids of NLTE high gravity model atmospheres and optically thick accretion disk models for the first time to archival IUE and FUSE spectra of the S-type symbiotic variable EG And taken at superior spectroscopic conjunction when Rayleigh scattering should be minimal and the hot component is viewed in front of the red giant. For EG And's widely accepted, published hot component mass, orbital inclination and distance from the Hipparcos parallax, we find that hot, high gravity, NLTE photosphere model fits to the IUE spectra yield distances from the best-fitting models which agree with the Hipparcos parallax distance but at temperatures substantially lower than the modified Zanstra temperatures. NLTE fits to an archival FUSE spectrum taken at the same orbital phase as the IUE spectra yield the same temperature as the IUE temperature (50,000K). However, for the same hot component mass, inclination and parallax-derived distance, accretion disk models at moderately high inclinations, $\sim 60-75^{\circ}$ with accretion rates $\dot{M} = 1\times 10^{-8}$ to $1\times 10^{-9} M_{\sun}/yr$ for white dwarf masses $M_{wd} = 0.4 M_{\sun}$ yield distances grossly smaller than the distance from the Hipparcos parallax. Therefore, we rule out an accretion disk as the dominant source of the FUV flux. Our findings support a hot bare white dwarf as the dominant source of FUV flux.

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