Modeling Forbidden Line Emission Profiles from Colliding Wind Binaries

R Ignace, R Bessey, C S Price

Department of Physics and Astronomy, East Tennessee State University

This paper presents calculations for forbidden emission line profile
shapes arising from colliding wind binaries. The main application
is for systems involving a Wolf-Rayet (WR) star and an OB star
companion. The WR wind is assumed to dominate the forbidden line
emission. The colliding wind interaction is treated as an archimedean
spiral with an inner boundary. Under the assumptions of the model,
the major findings are as follows. (a) The redistribution of the
WR~wind as a result of the wind collision is not flux conservative
but typically produces an excess of line emission; however, this
excess is modest at around the 10% level. (b) Deviations from a
flat-top profile shape for a spherical wind are greatest for viewing
inclinations that are more nearly face-on to the orbital plane. At
intermediate viewing inclinations, profiles display only mild
deviations from a flat-top shape. (c) The profile shape can be
used to constrain the colliding wind bow shock opening angle. (d)
Structure in the line profile tends to be suppressed in binaries
of shorter periods. (e) Obtaining data for multiple forbidden lines
is important since different lines probe different characteristic
radial scales. Our models are discussed in relation to {em Infrared
Space Observatory} data for WR~147 and $gamma$~Vel (WR~11). The
lines for WR~147 are probably not accurate enough to draw firm
conclusions. For $gamma$~Vel, individual line morphologies are
broadly reproducible but not simultaneously so for the claimed wind
and orbital parameters. Overall, the effort demonstrates how lines
that are sensitive to the large-scale wind can help to deduce binary
system properties and provide new tests of numerical simulations.

Reference: to appear in MNRAS
Status: Manuscript has been accepted