IRCS camera filters
The following table lists the filters available in the camera section of IRCS, together with their sensitivities. The transmission curves of each filter are available as plots or ASCII lists (lists kindly provided by Alan Tokunaga of the IRTF) if indicated in the respective columns.
All sensitivity figures are for 5 sigma detections in 1 hour of on-source integration with the infrared secondary mirror. They assume background-limited performance (see the guide for exposure time estimation). Point source sensitivities assume 0.5'' seeing and a 1.0'' diameter extraction aperture; extended source sensitivities are per pixel (the first column is for the 20 mas pixel scale, the second for the 52 mas pixel scale); binning over N pixels will improve the sensitivity by 1.25 log N mag.
Observers should be aware that variations in the strength of the OH airglow can cause changes of up to 1 mag in the sky background, with significant changes in sensitivity.
(1) The sensitivities for w/ AO will be improved about 1-2 magnitude with full AO correction. Please check the improvement with Imaging ETC with seeing ~ 0.1", aperture ~ 0.2" - 0.3" parameters.
The following amounts are estimated while a filter was cold and tilted by 5 degrees in IRCS (except Br gamma filter).
(1)Transmittance at room temperature.
The Transmission Curves of the ND Filter installed in the Filter Wheel 3
There are two ND filters installed for IRCS, one each in the filter wheel 1 and 3. Although we do not recommend to use this filter in combinations with any other filter for scientific photometry, it is often used for bright objects along with other filters. For its transmission curves throughout the IRCS wavelength coverage, please refer to this plot.
The Shift of Transmission Curve within the FOV
The actual wavelength coverages for these filters will change as a function of the angle of incidence (AOI) to the filter. This mean that the filter transmission will have the significant dependence with the position on the image, especially for narrow-band fileters. You can refer to these plots for the transmission shifts of several NB filters. Regarding the informations for the other filters, please contact the support astronomer.