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Because the WHIRC filters are not the "standard" size, the vendor did not obtain cryogenic transmission information on the actual filters in the instrument. Instead, the vendor measured both ambient (300 K) and cold (77 K) transmission of a 25 mm diameter witness sample (which fits into their variable-temperature filter holder) and used the shift in the transmission characteristics with temperature to calibrate the 300 K transmission curve of the actual filter to a calculated curve at 77 K. These numbers are the center wavelength and bandpass presented in the Table.
The average transmission in the table was calculated by integrating under the ambient transmission curves and dividing by the vendor-calculated cryogenic FWHM.
The tracings on the links below are the 300 K transmission plots of the actual WHIRC filters.
The complete set of vendor scans has been compiled into a spreadsheet for downloading.
|Filter||λ (μm)||Δλ (μm)||tavg|
|Pa β 45||1.303||0.0133||0.863|
|[Fe II] 45||1.668||0.0162||0.917|
|Br γ 45||2.188||0.0237||0.940|
Note: The Pa β 45 and CO-n filters were removed from WHIRC in January 2012 and replaced by the CN and CO-w filters.