Focus sweep data

We had a unique diagnostic tool for determining whether or not the secondary was fractured during the dark run in that we had 3 sets of focus sweep data for the imaging camera taken on the nights of 05 October 1999, 11 October 1999, and 14 October 1999. The sweeps consisted of images from which a range from nominal focus to $\pm300 \mu$ m for the secondary. The files were obtained from the backup tapes by Snedden for images that were -300 $\mu$ m out of focus. Four images were obtained from each focus sweep; 1) CCD g1, at the trailing corner of the CCD array; 2) CCD g3, near the middle of the trailing edge; 3) CCD u1, at the edge of the central row of CCDs; 4) CCD u3, near the center of the CCD array. The gray-scale images are found below: see Figures 7 to 18. In addition, we have, for the sake of completeness included pseudo-3D plots of the same doughnuts in Figures 19 through 30.

**Figure:** 05 October 1999, CCD g1
$\begin{figure} \centerline{ \psfig {figure=blowup_992_g1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD g3
$\begin{figure} \centerline{ \psfig {figure=blowup_992_g3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD u1
$\begin{figure} \centerline{ \psfig {figure=blowup_992_u1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD u3
$\begin{figure} \centerline{ \psfig {figure=blowup_992_u3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD g1
$\begin{figure} \centerline{ \psfig {figure=blowup_1027_g1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD g3
$\begin{figure} \centerline{ \psfig {figure=blowup_1027_g3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD u1
$\begin{figure} \centerline{ \psfig {figure=blowup_1027_u1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD u3
$\begin{figure} \centerline{ \psfig {figure=blowup_1027_u3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD g1
$\begin{figure} \centerline{ \psfig {figure=blowup_1051_g1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD g3
$\begin{figure} \centerline{ \psfig {figure=blowup_1051_g3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD u1
$\begin{figure} \centerline{ \psfig {figure=blowup_1051_u1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD u3. The white pixels are saturated in this image.
$\begin{figure} \centerline{ \psfig {figure=blowup_1051_u3.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD g1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=992_g1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD g3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=992_g3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD u1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=992_u1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 05 October 1999, CCD g3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=992_u3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD g1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1027_g1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD g3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1027_g3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD u1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1027_u1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 11 October 1999, CCD u3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1027_u3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD g1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1051_g1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD g3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1051_g3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD u1. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1051_u1_surf.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** 14 October 1999, CCD u3. **Surface** plot.
$\begin{figure} \centerline{ \psfig {figure=1051_u3_surf.ps,height=3.5in,angle=-90} }\end{figure}$

Morphologically, the out-of-focus doughnuts from the 3 nights are quite similar, but a more quantitative analysis was thought desirable, so Snedden calculated a series of normalised brightnesses (after sky subtraction), in radial cuts through each of the doughnuts for CCDs g1 and g3, and compared the different nights to each other. All measured stars were chosen to be of approximately the same brightness. In Figure 31, are plotted the normalised brightness at the various cuts for the 3 nights in question for CCD g1. Figure 32 plots the same data but for CCD g3. The error bars are based on multiple measurements of 2 or more stars on an image.

We notice immediately that the data from the night of 05 October 1999 is systematically offset, and generally has a higher value than either of the other two nights. This could be interpreted as: 1) the seeing and atmospherics on the night of 05 October were better than the succeeding nights; 2) the fracture occurred sometime between the nights of 05 October 1999 and 11 October 1999, but lead to only a minor amount of image degradation; 3) we placed a stress on the secondary between the nights of 05 October 1999 and 11 October 1999, but this did not result in the immediate fracture of the secondary - the temperature drop was the final ingredient needed; 4) the focus was slightly better and the values were binned differently so that the resulting flux distribution was flatter. What is of interest is that the nights of 11 and 14 October 1999 both trend quite closely to each other, with the exception of the angular shift of the brightest regions. Because of the uncertainties in the measurements, we cannot say that the differences between 05 October and the other two nights are absolutely definitive evidence for the fracture occurring as mentioned in option 1 above, only somewhat suggestive.

**Figure:** Comparison of normalised brighness for the out-of-focus doughnuts for the nights of 05, 11, and 14 October 1999 for CCD g1. We note the trends are quite similar for each night, and that the night of 05 October 1999 is systematically different then either of the two other nights.
$\begin{figure} \centerline{ \psfig {figure=donut_g1.ps,height=3.5in,angle=-90} }\end{figure}$

**Figure:** Comparison of normalised brighness for the out-of-focus doughnuts for the nights of 05, 11, and 14 October 1999 for CCD g3. Again note that the night of 05 October 1999 is systematically different then either of the two other nights.
$\begin{figure} \centerline{ \psfig {figure=donut_g3.ps,height=3.5in,angle=-90} }\end{figure}$