IRS Throughput Data

The data on throughput provided here was taken on 17Oct97. This data
reflects the effect of the detector installed at end of 1996 and, more
recently, the effects of the optics modifications enable the IRS to
work at f/14.5 with the new tip-tilt secondary.

The data were taken with a 2mm slit to avoid slit-edge losses. The data
presented here are extracted by summing all of the pixels in the
cross-dispersion direction with significant signal.  (Typically,
depending on seeing, the light will be distributed over ~3+ pixels).

The graphs here are normalized to the case of a 7th magnitude star (in
each band) and divided by the integration time and spectral bandwidth
per pixel to provide a measure of throughput which is independent of
dispersion.

The bias of the detector was in all cases 0.55 volts, (the recommended
value for all conditions except for very high background).

A summary of all the data is compact and useful:
 winsum.ps winsum.gif

A clean laser print of the postscript file is
mostly legible. The illegible exponent in the graph is 6!

The data were taken using the 75 line 4.5 micron blaze grating and the
cross-dispersed grating. The 75 line data was obtained with the G8III
star BS9054. The Cross-dispersed spectrum is of the CTIO IR photometry
standard star HD19904.

The individual graphs are also available separately;

Cross dispersed grating:
K band (3nd order) xd_K.ps xd_K.gif
H band (4rd order) xd_H.ps xd_H.gif
J band (5rd order) xd_J.ps xd_J.gif
I band (6th order) xd_I.ps xd_I.gif

75 line grating (4.5 micron blaze):
K band (2nd order) 75_K.ps 75_K.gif
H band (3rd order) 75_H.ps 75_H.gif
J band (4th order) 75_J.ps 75_J.gif

Brooke Gregory 22Dec97