HIRES has two 12 position filter wheels that reside immediately behind the decker plate. Their primary function is to block unwanted orders from the cross-disperser. Each filter wheel has a "clear" position that is empty. Proper choice of blocking filters is critical for isolating particular regions of interest. The Table below gives some useful combinations of filter choice for given spectral regions. Note that each combination of filters requires refocusing of the collimator which is handled automatically if installed from the XHIRES GUI. Clicking the link on one of the filter names in the table will bring up a plot of the estimated transmission of the filter and atmosphere as a function of wavelength.
| Cross-disperser Order | Wavelength (microns) | Filter Wheel 1 | Filter Wheel 2 |
|---|---|---|---|
| 1 | 0.69 - 1.1 | 2 (RG610) | 1 (clear) |
| 1 | 0.63 - 1.1 | 3 (OG530) | 1 (clear) |
| 1 | 0.53 - 1.1 | 4 (GG475) | 1 (clear) |
| 1 | 0.48 - 1.1 | 5 (KV418) | 1 (clear) |
| 1 | 0.44 - 1.1 | 6 (KV408) | 1 (clear) |
| 1 | 0.39 - 1.1 | 8 (KV380) | 1 (clear) |
| 1 | 0.35 - 1.1 | 9 (KV370) | 1 (clear) |
| 1 | 0.30 - 1.1 | 11 (WG335) | 1 (clear) |
HIRES has two filter wheels in front of the guide CCD (an E2V CCD47) which can be used to limit the spectral range used during guiding. The first wheel contains six filters (Schott bg24a, gg495, rg610, bg23+dt, bg38, and dt). The second wheel contains another dt filter, several neutral density filters, and a clear slot. The dt filter in the second wheel can be used in combination with the filters in the first wheel.
The list below shows common filter combinations with links to the estimated response of the system (including the atmospheric transmission and CCD QE) as a function of wavelength.
| Wheel1 | Wheel2 | Estimated Response Plot |
|---|---|---|
| bg24a | none | Guider Response Curve |
| gg495 | none | Guider Response Curve |
| rg610 | none | Guider Response Curve |
| bg23+dt | none | Guider Response Curve |
| bg38 | none | Guider Response Curve |
| dt | none | Guider Response Curve |
| bg24a | dt | Guider Response Curve |
| gg495 | dt | Guider Response Curve |
| rg610 | dt | Guider Response Curve |
| bg38 | dt | Guider Response Curve |
The lamps in the instrument also have filters to modify their output. The response curves of those filters are provided below.
