THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996

4. Report on Operations

4.4. Instruments

4.4.4. Accessories

The performance of the recently commissioned IRPOL2, both with IRCAM3 and CGS4, was one of the great successes of UKIRT during late 1995 and 1996. Built at the University of Hertfordshire, IRPOL2, with its dual-beam feature, achieves an order of magnitude improvement in the sensitivity of imaging polarimetry and spectropolarimetry compared with previous polarimeters (including IRPOL1), placing UKIRT's infrared polarimetric capability in a class by itself. On-line data reduction routines are being written by UKIRT staff and will be made generally available in Semester 97A.

The first year of IRPOL2 on UKIRT was not entirely trouble-free. In particular, some IRCAM3 data obtained in 1995 showed a serious systematic problem -- measurements of bright sources produced significantly lower polarizations than their known values. After investigation by staff at the University of Hertfordshire and the JAC, the cause of the problem was identified as integrations beginning before completion of waveplate moves. For short exposure times this resulted in a large underestimate of polarisation, as observed. Affected IRPOL2 users have been informed of the problem and a software fix will be implemented in early 1997. ³

A new low resolution Queensgate Instruments Fabry-Perot etalon for the 2.0-2.5m band was successfully commissioned early in 1995. Apart from one electrical failure at the end of 1996, it has operated reliably and produced excellent science. The resolution of the Fabry-Perot is 300-350 km/s, lower than the value of 250 km/s which had been specified. Despite this, the etalon was accepted, because its other important characteristics (transmittance and thermal stability) are excellent.