Construction of a 1–3 micron infrared photometer and its test observations

We report on the design and construction of a l–3μ infrared photometer. We use a pre-focus rotating chopper to effect modulation and, unlike some previous designs, we use the chopper to feed in the sky background only, and use a fixed mirror to feed in the star signal. In this way, excess demand on the precision setting of the rotating chopper Is avoided. Test observations on a 1-m telescope show that our photometer is capable of observing all the IRC sources with an accuracy better than O.lmag at a time constant of 2 minutes.