This paper presents the first empirical measurement of the <i>K</i><sup>1</sup>-band effective wavelength and bandwidth of the
CHARA Classic beam combiner on the CHARA Array. Prior to this work, the accepted effective wavelength
value used for CHARA Classic data (2.1501μm) came from a model of the system; it was not derived from
measurements done on the system directly. We employ two data collection methods for our observations: using
the Optical Path Length Equalizer (OPLE) cart to scan through the interference fringes and using the dither
mirror to scan through the fringes. The two observational methods yield similar effective wavelength measurements
(2.141±0.003μm with the OPLE cart and 2.136±0.002μm with the dither mirror). Both of these results are lower than the previously adopted effective wavelength value, but by less than 0.7%. The bandwidth values
measured by the two methods differ from each other by almost 5% (0.334 ± 0.002μm with the OPLE cart and
0.351±0.003μm with the dither mirror). Our results establish the first estimate of the uncertainty in the effective
wavelength and bandwidth.
The Smithsonian Widefield Infrared Camera (SWIRC) is a Y -, J-, and H-band imager for the f/5 MMT.
Proposed in May 2003 and commissioned in June 2004, the goal of the instrument was to deliver quickly a wide
field-of-view instrument with minimal optical elements and hence high throughput. The trade-off; was to sacrifice
K-band capability by not having an internal, cold Lyot stop. We describe SWIRC's design and capabilities, and
discuss lessons learned from the thermal design and the detector mount, all of which have been incorporated into
the upcoming MMT & Magellan Infrared Spectrograph.