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Semi-empiric Radiative Transfer Modeling of FUSE Stellar Spectra

By SpaceRef Editor
May 8, 2005
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Astrophysics, abstract

From: A. Lobel [view email]
Date: Sun, 24 Apr 2005 03:43:41 GMT (71kb)

Semi-empiric Radiative Transfer Modeling of FUSE Stellar Spectra

A. Lobel (1),
E. H. Avrett (1),
J. P. Aufdenberg (2), ((1) Harvard-Smithsonian CfA, (2) NOAO)

Comments: 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)

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.

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