Vibrating Crow

Our CRO is a very fast f/1 optic, and our ASM makes an f/16 beam. So motions of the CRO are amplified by a factor of 16 in our focal planes. We can see this on the VisAO CCD47 as a dancing image due to small mechanical vibrations of the telescope.

The MagAO project is adding a little bit to the vibrations of the telescope, mainly with two cooling pumps. One pump circulates glycol for our CCDs and the Shutter, and the other keeps Clio2 cold. With the 16x CRO amplification, we really see the impact of these pumps. We recorded 60 sec time series of the CCD47 operating at 32Hz in a 64×64 subarray mode. Here are the results:

With both pumps off:

Unnormalized power spectrum of the x position of the VisAO image position. Note that I'm being lazy and not fully normalizing the PSD. With both pumps off, we had an rms jitter of 2.2 pixels.

With the Clio2 pump off, and the CCD pump on:

Here we see more white noise, but no strong resonances and the image is fairly stable by eye. Rms jitter was 5.4 pixels.

With the Clio2 pump on, and the CCD pump off:

The Clio2 pump excites a ~2.3 Hz resonance. We think this is due to the rack holding the pump sitting on a beam connected directly to the telescope. Rms jitter in this configuration was 9.5 pixels

We are actually very happy with the vibration performance of the system attached to Clay. Taking into account the factor of 16 for the CRO reflection, we expect to have only a few milli-arcsec of jitter when we observe actual stars. We have also taken measurements with our internal artificial star without the CRO and confirmed this. Good news, especially for VisAO.

Another experiment we conducted was having the PI bounce around the control room. He has a noticeable effect.

Time series of the VisAO centroid x position, with some input from the PI.

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