Entrance Apertures

The apertures are arranged on the plate in five groups. Each group comprises five apertures of a single width at different heights. Apertures are selected in accordance with program requirements and observing conditions. Choosing the best aperture for your needs is discussed in the Setup Procedures section of this manual.
Occasionally, Hamilton observations require spatial resolution not possible with the aperture plate's limitation on slit height. In such cases the aperture plate is removed and the old slit jaws are used in a techinique called longslit observation. Longslit observations trade wavelength coverage for spatial resolution and have special setup and operating requirements.
The table below lists the available aperture widths, given in arcseconds on the the sky at the 3-meter and CAT plate scales, in pixels as projected on the detector (assuming 15-micron pixels), and their actual widths in microns.
Aperture Widths | |||||
---|---|---|---|---|---|
apertures | B-F | G-K | L-P | Q-U | V-Z |
arcsecs, 3-m scale | ~ 0.6 | ~ 0.8 | ~ 1.2 | ~ 1.5 | ~ 1.8 |
arcsecs, CAT scale | ~ 3.0 | ~ 4.0 | ~ 6.0 | ~ 7.5 | ~ 9.0 |
pixels | ~ 0.5 | ~ 0.66 | ~ 1.0 | ~ 1.25 | ~ 1.5 |
microns | 320 | 400 | 640 | 800 | 960 |
Each of the five widths is available in five heights: 2.0, 2.5, 3.0, 5.0, and 6.0-arcseconds at the 3-m plate scale, for a total of 25 apertures labeled B-Z. Aperture A is 100-microns wide by 2.5-arcseconds, and is used exclusively for focusing.
Aperture choice is controlled using the spectrograph motor control software, hammotor_gui (see Figure 1 for the aperture selection choices). The letter identifiers for the apertures are not listed in the motor control interface, but go in order from A 100:25 through Z 960:6.0. To do longslit observations set the aperture to Out, and adjust the slit width to the desired setting in microns using the Slit section of the hammotor GUI (shown in Figure 2).

Figure 1: Aperture Plate Selection Menu
Figure 2: Slit Size
Support Astronomers (sa@ucolick.org) Last modified: Sun Feb 13 16:49:16 PST 2011