Subject: Br-gamma filter in GRIM II

From: Alan Watson

Submitted: Tue, 28 Jan 1997 13:52:02 -0700

Message number: 33 (previous: 32, next: 34 up: Index)

The documentation for GRIM II includes two different curves for
filters that could be the 2.17 micron Br-gamma filter. One is dated
1987, has a peak transmission of 0.69, and a FWHM of 0.029 microns.
The other is dated 1992, has a peak transmission of 0.79, and a FWHM
of 0.022 microns.

To determine which one is actually in the instrument, I took ratios of
f/10 spectra of the dome incandescents through the 2.12, 2.17, 2.25,
2.30, and K filters. I used the lab K transmission to estimate the
peak transmissions and also measured rough FWHM.

    Filter                          2.12    2.17    2.25    2.30
    K transmission (lab)            0.75    0.75    0.72    0.72
    Peak transmission (this work)   0.56    0.65    0.78    0.75
    Peak transmission (lab)         0.62            0.78    0.75
    FWHM (this work)                0.030   0.028   0.025   0.026
    FWHM (lab)                      0.029           0.024   0.027

I think these measurements are most consistent with the 1987 curve,
especially since my measurement of the peak transmission of the 2.12
filter is a bit lower than the lab measurement.

Regards,

Alan Watson
APO APO APO APO APO  Apache Point Observatory 3.5m  APO APO APO
APO
APO  This is message 33 in the apo35-grim archive. You can find
APO  the archive on http://www.astro.princeton.edu/APO/apo35-grim/INDEX.html
APO  To join/leave the list, send mail to apo35-request@astro.princeton.edu
APO  To post a message, mail it to apo35-grim@astro.princeton.edu
APO
APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO