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

Photon Integrator

Figure 1: Integrator Control Panel

The Photon Integrator predates the Hamilton spectrograph, having been originally designed as an exposure meter for photographic plates taken with the old coudé spectrometers. It may optionally be used to estimate the progress of Hamilton exposures, and is now also used -- in conjunction with new software, Showmidpoint -- to provide an exposure's photon-weighted midpoint to aid with barycentric correction of precision radial velocity measurements.

The integrator uses a rapidly rotating propellor/chopper, located just behind the entrance slit, to divert ~6.5% of the light passing through the slit to a photomultiplier tube (PMT). The signal from the PMT gives an instantaneous measure of the throughput at the slit, and is electronically integrated to give a running, cummulative level for the exposure.

To operate the integrator one should use the following procedure.

  1. Make sure the "Dimmer Power" and "Shutter" switches are on (i.e. toggle switches are up, see Figure 2 below).
  2. Turn on the integrator. The power switch is located on the lower right of the integrator panel (see Figure 1).
  3. Check the shutter, brightness, and multiplier dials to make sure they are properly set for your program. The usual settings are one step above "Faint", 0.1 multiplier, and Open shutter. Rarely are other settings necessary.
  4. Before turning on the PMT power, make sure the voltage dial on the right is set to zero (Figure 3).
  5. Turn on PMT power supply. Slowly turn the dial to 705. This corresponds to a reading of ~137 on the display (Figure 4).
  6. Pull the plunger (Figure 5) for the chopper to start it rotating (you should be able to hear the faint whir of its motion). You should also hear beeps from the integrator panel for each count detected by the PMT.

Figure 2: Dimmer Power and Shutter switches should always be on (toggle switch in up position).

Figure 3: PMT Power Supply, voltage dial set to zero.

Figure 4: PMT Power Supply, voltage dial set to 705.

Figure 5: Integrator Chopper Plunger.

The PMT is very sensitive to light and you do not want to subject it to the bright light of the arc lamps or quartz flat field lamp. You may protect it by closing its shutter (the switch is on the integrator panel) or by not turning on the PMT until you are ready for night time operations (this is the more common tactic so that the shutter won't accidently be left closed for data taking).

When done with the integrator at the end of the night, shut it down in the following procedure.

  1. Push in the plunger. This ensures that the chopper is parked out of the way of the slit and will not block the light for future observers not using the integrator (Figure 5).
  2. Turn the PMT dial down to zero (Figure 3).
  3. Turn off PMT power supply (Figure 3).
  4. Set Shutter switch on Integrator Panel (Figure 1) to Closed.
  5. Turn off integrator (Figure 1).

The photon integrator hasn't been fully characterized, but preliminary testing (Feb 2021) gives the following count rates on the detector:
5.5 DN/pix/PMT count @ 5500A for a B-V=0.0 star
9.5 DN/pix/PMT count @ 7500A for a B-V=0.0 star
with the standard settings. Redder stars appear to generate higher DN/pix/PMT count and bluer stars fewer at the sampled wavelengths, but has not yet been calibrated.

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Last modified: Mon Feb 22 19:01:29 PST 2021