The Bonn WWFPP (Weit-Winkel-Flächen-Photometer/Polarimeter)

A focal reducer system for the 1.23m telescope at the Calar Alto Observatory.

The WWFPP was designed and built at the Astronomical Instituts of the University of Bonn. It allows photometric and polarimetric observation over a large field. The Calar Alto 1.23 m telescope offers an undistorted field of view (without correction optics) of about 0.5 degree diameter. The WWFPP optics were designed to image about 75% of this field size onto a 2kx2k 15µm pixel CCD-detector (field diagonal: 28.5', pixel size: 0.60").

The WWFPP has been developed to become a common user instrument. The instrument has been realized in part through grant 05BN414 of the Federal Ministery of Science and Technology, grant Bo 779/6 of the Deutsche Forschungsgemeinschaft and MWF IVA5 of the Land Nordrhein-Westfalen After several observing campaigns in 93/94/95 with astrometric measurements as well as photometric and polarimetric observations it will be made available to the community.

The WWFPP is based on a focal reducer system (f/4.0) with filters (B,V,R,I, H-alpha) and polarization optics (twin wollaston prism) in the collimated beam section. The filter wheels are mounted in drawer-like units (image: opened filterwheel drawer). Two of these units are contained in the filter wheel box. They can be exchanged individually to exchange complete filter systems in the future. Polarizers are mounted on these wheels too. Four movable masks for polarimetry and internal calibration purposes are placed in the plane of the telescope cassegrain focus. They can be moved in x and y in steps of 12µm. Tests in the workshop and at the telescope have proven the WWFPP to be mechanically stable, in spite of its length of 108 cm . The image shift over the CCD is below 1/4 pixel for a 1-2 h exposure. The sensitivity of the overall system for stellar objects is as expected from quantitative estimates. From a 19 mag object we get in the V band about 1000 electrons after 100 sec of exposure time (frontside illuminated LORAL CCD).

The total length of the WWFPP leads to some restrictions of the telescope movement. Nevertheless, using the reversion mode of the telescope, sky coverage is not restricted.

See also:


Last Update: August 13, 1997
Klaus Reif (E-mail: reif@astro.uni-bonn.de)