A Simple Polarimetric System for the Lick Observatory Image-Tube Scanner

The insertion of a simple, stationary, three-element filter in front of the Cassegrain spectrograph and image-tube scanner (ITS) of the Lick 120-inch telescope allows simultaneous measurement of the Stokes parameters as a flinction of wavelength across at least 2000 A. Resolution for linear polarization varies from 25 A at 3100 A to 175 A at 8000 A, while the instrumental polarization is less than 0.2%. Simultaneous sky subtraction, small slit, and online reduction of incoming data already achieved in the ITS system make this a useful spectropolarimetric device for faint objects.