User's Guide to the Hamilton Spectrograph

Table of Contents

Quick Reference
CCD Characteristics
Grating Tilt & Dewar Height
Filter Wheel & Shutter
Calibration Sources
Photon Integrator
Image Rotator
Iodine Cell & Slit Room Controller
Guide Camera & Filter Wheel
Data Taking System
Hamilton Motor Controller
Hamilton Focus
More Info:
Spectral Format
Navigating the Spectrum
Table of Orders
Setup Procedures
Observing Hints

Data Archive
Mt. Hamilton Homepage

Entrance Apertures

The Hamilton was originally designed with conventional slit jaws, surmounted by a stepped decker to limit slit height. (Because the echelle format consists of many spectral orders, slightly separated by cross dispersion, slit height must be limited to prevent orders overlapping one another.) Slit and decker have been functionally replaced with a selection of precise rectangular openings in a polished steel aperture plate, which offers the observer a variety of height/width combinations. (The slit is still present, but when the aperture plate is selected in software, the jaws are automatically opened to their maximum width so as to be entirely clear of the light path.)

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
aperturesB-FG-K L-PQ-UV-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
microns320 400640800 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

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Last modified: Sun Feb 13 16:49:16 PST 2011