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The infrared photometer-spectrometer, IRPS

IRPS was the first infrared instrument to be developed for the AAT, and introduced a novel design of electronic control for InSb detectors which gave it both impressive sensitivity and great versatility. Barton and Allen (1987 PASP 92, 368) give a detailed account of the instrument.

IRPS is no longer used as a standalone instrument.  Its functions have been mostly superseded by IRIS, and we do not offer it as a general user instrument.  It is still used with the Hatfield polarimeter however to provide the infrared channel for that instrument.  Estimates of the performance of IRPS are given below.  

Five standard broad-band filters are installed, as listed in Table 8.4. For further information on the wavebands, including colour corrections, see Bessell and Brett (1988 PASP , 1134).

 
Table: Wavebands for IR photometry

The sensitivity limits quoted are for 3 sigma after 30 minutes of integration. This is about the longest one should spend on a single measurement, but actually the sensitivity limits fluctuate because the sky brightness is not constant. In summer the longer wavelengths fare less well, and around sunspot maximum J and H are worsened. Atmospheric extinction is slightly higher in summer and less in winter. At J and M, the extinction is sensitive to humidity.

A list of standard stars for JHKL' (Allen and Cragg 1983 MNRAS 203, 777) can be called up by name through the telescope control computer. Magnitudes are listed in the users' manual.

The dewar is limited to aperture sizes smaller than 8" diameter. If the seeing (in the visible) exceeds about 3", photometric accuracy better than ~ 2% cannot be attained. Obviously, photometric weather is necessary to do photometry.


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