SAAO - South African Astronomical Observatory

Infrared Photometer (Mk II)

The Mk II infrared photometer is an improved version of the Mk I, designed primarily to cover the JHKL bands (1.25, 1.6, 2.2 and 3.4 microns). It uses an InSb cell cooled with nitrogen slush, and a sectored mirror focal plane chopper.

Data acquisition is via the program BRUCE, which runs in DOS on the 486 PC. BRUCE also provides online reductions, making corrections for atmospheric extinction and for zero-point. Comprehensive lists of appropriate JHKL standard star magnitudes should be available in the dome, but the wary observer may wish to get a copy in Cape Town. This is an updated version of the data published by Carter (1990, MNRAS 242, 1). It is recommended that during the course of the observing the photometry is recorded on the PC hard disk and printed out on the printer provided. The data can be transferred to Cape Town on a floppy disk where a full reduction for each individual night will be made. A chart recorder output of the signal is also available, and is especially useful for setup, observing IR-bright but otherwise invisible objects, and for cloud monitoring.

A full description of the Mk I photometer, which is very similar to the Mk II, can be found in Glass, MNRAS 164, 155, 1973.


Mk II System Parameters




1, 1.5, 2.0, 3.0, 4.0 mm diameter


InSb photoconductor

Fabry lens

Calcium flouride

Chopping speed

12.5 Hz

Acquisition field

40 mm diameter (about 12 arcmin)

Integration time

Adjustable, normally 10 seconds


10% accuracy at K = 10.4 after 4 modules (160 s) with a 2.0 mm (37 arcsec) aperture.