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Emission line profile shapes from anisotropic resonance line scattering in planar equatorial disks
Received 10 March 1998 / Accepted 12 June 1998
The consequences of anisotropic resonance line scattering for the emission profiles of equatorial disks are considered. In particular the opportunity to infer the disk velocity field owing to the anisotropic scattering is discussed. Analytic expressions for the profile shapes are derived for the cases of constant expansion and rotation, and numerical results are given for more realistic disk velocity fields of linear expansion and Keplerian rotation. The essential result is that the anisotropic line scattering produces a different profile signature in expanding disks as compared to rotating disks, owing to the difference in the isovelocity pattern of the two cases and how the two respective patterns relate to the scattering geometry. Unlike the spherical case discussed in a preceding paper, the anisotropic effects are more significant (up to 10-20%) in disk geometries because the degree of stellar occultation depends on viewing inclination. The key to using the formulae presented here is to obtain profiles of lines that have differing degrees of anisotropic scattering. In particular, strong doublets of Lithium-like atoms (e.g., CIV 1548,1550, MgII 2796, 2803, CaII 3935, 3969 to name a few) are well-suited for comparison, with the long wavelength component scattering isotropically and the short wavelength component being partially dipole scattering. Consideration of such doublets are advantageous in that the two components arise from the same spatial location in the flow, whereas the spatial coincidence of formation for two completely different lines is not assured. Owing to several simplifying assumptions, direct application of the results presented here to observations requires somewhat restrictive conditions, yet the diagnostic potential of the method does appear promising, especially for multiplets.
Key words: line: profiles techniques: spectroscopic circumstellar matter stars: early-type stars: emission-line, Be stars: rotation
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Online publication: August 27, 1998