Filters and Grisms
Filters
A number of filters have been installed in the two filter wheels. Basic specifications and characteristics for the available filters are listed below.
| Name |
Central Wavelength (µm) |
FWHM (µm) |
Peak Transmission (percent) |
|---|---|---|---|
| J | 1.238 | 0.271 | 82 |
| H | 1.656 | 0.296 | 85 |
| K | 2.195 | 0.411 | 75 |
| KS | 2.150 | 0.320 | (1) |
| H2 1-0 S(1) (H2-2.122) | 2.125 | 0.020 | 80 |
| H I (n=7-4) (BrG-2.16) | 2.167 | 0.020 | 78 |
| J CH4 (CH4-1.2) | 1.183 | 0.040 | 86 (2) |
| K CH4 (CH4-2.4) | 2.356 | 0.130 | 80 |
| 2.2/0.04 | 2.192 | 0.047 | 79 |
| H cont | 1.570 | 0.020 | (1) |
| [Fe II] | 1.644 | 0.016 | (1) |
| K cont | 2.270 | 0.020 | (1) |
Notes:
(1)Specified, not measured.
(2)Unblocked, needs to be crossed with the J filter for blocking.
Transmission curves for many of the filters are shown below.
Click for full-sized image. |
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Click for full-sized image. |
Filter and Aperture Positions in IRCAL
The following filters and apertures are mounted in IRCAL:
| Filter1 | Filter2 | Aperture |
|---|---|---|
| Home | Home | Home |
| Open | KSiGrism-2 | Pinhole-100um |
| J | Wollaston | Slit-100um-V |
| H | K | Half-field |
| Ks | Ch4-2.4 | Open |
| H2-2.122 | CH4-1.2 | Slit-100um-H |
| BrG-2.16 | Open | Finger |
| FeII | Blank25 | Open(F) |
| CaF-Kgrism | HGrism |
Please note that Home Positions are not the same as Open.
There is not enough space in IRCAL to have all filters mounted and available.
If you want to use a specific filter or grism, please be sure to request it
on your telescope time proposal.
Grisms
A 5 mm pupil size was chosen as a compromise between instrument size, and the ability to do grism spectroscopy. With a 5 mm pupil, it is possible to do moderate resolution spectroscopy with a calcium fluoride and resin replica grating grism. R=700 is chosen to fit the full bandpass of the J, H, or K atmospheric windows across 256 pixels with 2 pixel spectral resolution.A high resolution silicon grism has been installed in the camera for testing, but is not available for general observer use.
Polarimeter
A Wollaston prism and waveplate have been installed to allow polarimetry observations. The Wollaston prism is installed in the filter wheel (and should be used with the Half-field aperture stop). The waveplate is mounted immediately in front of IRCAL. Rotation of the waveplate is controlled through an IRCAL script, or directly through the AO motor control software.
Elinor Gates Last modified: Fri Mar 2 14:02:58 PST 2007