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\newpage{Marshall Cohen's Research Interests}
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	Cohen's current research is mainly concerned with active 
	galactic nuclei.  In these studies the first need is to describe 
	the nuclear region.  What components are there, what is the disposition 
	of disks and torii, is the outflowing material 
	in a wide cone or perhaps held close 
	to the equatorial plane, what fraction of quasars and galaxies 
	have extended scattering regions, etc.  The second need, then, is to 
	understand this phenomenology in terms of physics, and of course the 
	two tracks are pursued simultaneously. \p
	
	The observational program aimed at these goals is mostly built around 
	spectropolarimetry at the Hale and Keck telescopes.  As an example, the 
	figure shows spectra for a broad-absorption-line quasar, 0105-265, taken at 
	the Keck telescope.  The top panel shows the total flux and the lower 
	panel shows the fractional linear polarization.  Five broad 
	absorption troughs are visible; they are due to the atomic species 
	C IV, Si IV, Ly alpha/N V, O VI, and S VI.  The polarization increases 
	in these absorption featuers, and decreases in the emission 
	features.  A simple explanation for this might involve two components.  
	One is the 
	unpolarized continuum+line radiation which passes through material 
	flowing out near the equatorial plane; this material absorbs at the 
	various resonance wavelengths.  The other is continuum light from the 
	nucleus which is reflected from electrons or dust located, perhaps, 
	high on the axis.  The reflected light is strongly polarized and makes 
	up most of the light in the troughs, but only a fraction of the 
	continuum light and an even smaller fraction of the total light in the 
	emission lines.  This simple picture turns out to be deficient in 
	several ways, and a more complicated explanation is currently being 
	investigated. \p
	
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