Semi-empiric Radiative Transfer Modeling of FUSE Stellar Spectra

Lobel, A.; Avrett, E. H.; Aufdenberg, J. P.

Semi-empiric Radiative Transfer Modeling of FUSE Stellar Spectra

Authors

Lobel, A.

Avrett, E. H.

Aufdenberg, J. P.

Description

We present an overview of radiative transfer modeling efforts to interpret spectra of a variety of stellar objects observed with FUSE. Detailed radiative transfer modeling of high ion emission line profiles of C III and O VI observed in the far-UV spectrum provides a powerful means to probe the thermal and dynamic properties of high-temperature plasmas in the atmospheres of stars. We model asymmetric emission lines of C III lam977 observed in spectra of luminous cool stars such as Alpha Aqr, to infer the wind- and microturbulence velocity structures of the upper chromosphere. Semi-empiric radiative transfer models that include transition region temperature conditions, are further developed based on detailed fits to O VI resonance emission lines in the supergiant Alpha Aqr, the classical Cepheid variable Beta Dor, and to self-absorbed O VI emission lines in the cataclysmic variable SW UMa. We observe that the C III resonance line profile of Alpha Aqr assumes a remarkable asymmetric shape, reminiscent of P Cygni type profiles observed in hot luminous supergiants. The model calculations indicate outflow velocities above ~140 km/s at kinetic temperatures of 65 kK and higher. Based on detailed model fits to the narrow red-shifted and self-absorbed O VI emission lines of SW UMa we compute that the gas- and electron-density exceed the density conditions of the upper solar transition region by about three orders of magnitude. We discuss how detailed semi-empiric fits to emission lines observed with the high spectral resolution of FUSE can provide reliable constraints on the mass-loss or mass-accretion rates in these objects.
3 pages, 3 figures, Submitted for publication in the Proceedings of "Astrophysics in the Far Ultraviolet", 2nd FUSE Science and Data Workshop, Victoria, BC, Canada, Aug 2 - 6, 2004, ASP Conf. Ser., Eds. G. Sonneborn, W. Moos, & B.-G. Andersson, (in press)