Suggested Flat Exposure Times
40 l/mm grating:
| Wavelength | Order | BB Aperture | Exposure Tim (secs) |
|---|---|---|---|
| 1.15 | 2 | 5.0 | 2.0 |
| 1.30 | 2 | 5.0 | 2.0 |
| 1.70 | 1 | 1.3 | 0.6 |
| 2.20 | 1 | 1.3 | 0.25 |
| 3.10 | 1 | 3.2 | 0.75 |
| 3.80 | 1 | 2.0 | 2.0 |
| 4.90 | 1 | 1.3 | 1.0 |
150 l/mm grating:
| Wavelength | Order | BB Aperture | Exposure Time (secs) |
|---|---|---|---|
| 1.15 | 3 | 5.0 | 5.0 |
| 1.30 | 3 | 5.0 | 2.5 |
| 1.70 | 2 | 2.0 | 1.0 |
| 2.20 | 2 | 3.2 | 0.25 |
| 2.20 | 1 | 3.2 | 0.12 |
Echelle:
Because of the extremely small wavelength coverage of the echelle, it is fairly impracticable to provide a table of suggested blackbody apertures and exposure times. The quickets way to determine an appropriate exposure time and aperture is as follows (this technique can be used with any grating):
- Write an astronomical config for the wavelength you wish to observe at.
- Set to this config using the Set_Single_Observation menu in the CGS4 software and specify a flat observation.
- Select “Movie”, select an exposure time in “Set_Movie” (e.g., 0.5 secs) and then “Run_Movie”
- Note the counts on the movie screen.
- Select “Direct_Motor_Control” and select another blackbody aperture. You will see the counts change.
- When you are happy with your selection (i.e., 3000 – 4000 counts) abort the movie and edit your config with the appropriate numbers.
CGS4 Arcs
For a given wavelength, we do recommend that specific arc lamps are used. These will give the best coverage of unsaturated spectral lines. They are:
| Wavelength | Order | Recommended Lamp | Alternative Lamp |
|---|---|---|---|
| 1.15 | 2 | Krypton | Xenon |
| 1.30 | 1 | Krypton | Xenon |
| 1.70 | 1 | Xenon | Argon |
| 2.20 | 1 | Argon | Xenon |
| 3.10 | 1 | Xenon (2nd order) | Argon (2nd order) |
| 3.80 | 1 | Argon (2nd order) | Xenon (2nd order) |
List of available arc spectra.
Below is a list of arc spectra obtained with CGS4 at UKIRT. You may use these to help wavelength calibrate your CGS4 data both during and after your run. Currently, only low resolution spectra (75 l/mm grating, short focal length camera) are available on the web.
Lamp lines in the 3 to 5 micron region cannot be observed due to absorption by the lamp bulb glass. However, you can obtain lines in this region by observing 1 and 2 micron arc lines in 2nd order. In the spectra listed below, we have not indicated the wavelength value in 1st order for lines beyond 3 microns. If you are interested in this number, simply divide the indicated value by 2.
GIF files:
Argon
1.15um, 1.30um, 1.60um, 2.18um, 3.10um, 3.40um, 3.80um, 4.70um
Krypton
1.15um, 1.30um, 3.10um, 3.40um, 3.80um
Xenon
1.15um, 1.30um, 1.60um, 2.18um, 3.10um, 3.40um, 3.80um
PostScript files:
Shift-Click these to save them to local disk.
Argon
1.15um, 1.30um, 1.60um, 2.18um, 3.10um, 3.40um, 3.80um, 4.70um
Krypton
1.15um, 1.30um, 3.10um, 3.40um, 3.80um