TurPol was built at Turku Observatory by V.Piirola, based on his earlier design of such a photo--polarimeter. This later version has been in use at the NOT since March 1989. Photograph 1.1 shows the polarimeter at the telescope.
Figure: Photograph of the polarimeter on the telescope.
TurPol is a 5--channel photo-electric photo--polarimeter, allowing both photometry and polarimetry to be performed in 5 channels simultaneously. The permanently mounted filters are UBVRI. The pass bands are defined by four beam-splitters, and the UBVRI filters themselves. The use of beam-splitters gives a high throughput since they have very low absorption.
The instrument can be equipped with an achromatic half-- or a quarter wave plate, respectively for linear or circular polarisation measurements. With the quarter wave plate mounted it is also possible to do simultaneous linear and circular polarimetry.
By removing the calcite polariser from the beam, the instrument can be used for 5--channel sky chopping photometry.
TurPol is remotely controlled from a PC with a CAMAC interface crate during observations. The CAMAC crate and PC are in the control room.