SPECTROPOLARIMETRIC CALIBRATION OF CANARICAM: DEVELOPMENT OF A NETWORK OF CALIBRATION SOURCES FOR POLARIMETERS ON LARGE TELESCOPES

摘要

One of the calibration problems posed by the new generation of mid-infrared instrumentation on 8-10 metre class telescopes is that of polarimetric calibration. To be able to calibrate polarimetric data reliably it is necessary to be able to measure both the instrumental polarisation and the efficiency of detection of polarisation with a high degree of accuracy. In many senses the problems are less difficult than for spectrophotomet-ric calibration, but still need to be defined and overcome. In this work we discuss the polarisation calibration problems relevant to the mid-infrared, in particular to the CC-Pol module of CanariCam, the mid-infrared imaging spectrograph of the 10-m Gran Telescopio Canarias (GTC), although they are applicable to other similar infrared instruments. We show that the simplicity of the optical system is a key factor in ensuring a reliable mid-infrared calibration. The photon-starved field of mid-infrared polarimetry remains, post-ISO, perhaps the last unexploited portion of the optical/infrared region. With new advanced instrumentation on large telescopes we can expect many exciting observing opportunities in the next few years.