Spitzer Space Telescope - General Observer Proposal #3594


Determining Wolf Rayet Wind Structure from IRS Spectra 

Principal Investigator: Joseph Cassinelli
           Institution: University of Wisconsin-Madison

Co-Investigators: 
Henny Lamers, Astronomical Institute, University of Utrecht           
Richard Ignace, East Tennessee State University                       
Edward Churchwell, University of Wisconsin-Madison                    

Science Category: massive stars 
 Observing Modes: IrsStare 
  Hours Approved: 2.9 

Abstract:
We propose obtaining IRS spectra of a selection of 8 single Wolf Rayet
stars, of both WC and WN subclasses.  By observing spectral lines over
the broad range from 10  to 40  microns we will be able to study the
density concentrations or "clumpiness'' of the winds of WR stars over
a geometrically extended region.  This is because IR-radiation of
increasing wavelength, comes from increasingly higher layers in the
wind.  Knowing about the clumpiness is crucial for three reasons:  1.
the mass loss rates of WR stars derived from observed spectra depends
on the adopted clumping and the clumping seems to decrease with
distance 2.  clumpiness increases the possibility of photons to escape
and so it influences the applicability of the current WR wind models
that depend on multiscattering of the radiation field.  3.  It has
been discovered recently that the IR flux distributions (i.e.  the
spectral slope) of WR-stars depend in a systematic way on the spectral
subclass from WC 4 to 7 and WN 4 to 7.  The IRS spectra will provide
an explanation of this.  This will provide a basis for interpreting
the IRAC colors of the hundreds of WR stars that are expected to be
discovered in the GLIMPSE legacy survey of the Galactic plane.