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April 1999 Entrance Filter Failure Event

Image name: APR_99_Filter_Failure.png (click image to enlarge)
Image size: 12.2710 KB (512x700)
Date submitted: 12-Sep-2001


                 L. Acton, 12-Sep-2001

To the accuracy of the data it appears that the April 1999 entrance
filter failure happened at sunrise, as has been the case for several
other filure events.  This would suggest that thermal stress plays a
role in the failures.

The top panel displays the total signal in narrow-band straylight monitor
images with the 2-level intensity bifurcation normalized out.  In the
middle panel is the intensity in an exposure and resolution normalized
strip across the bottom of AlMg images.  The crosses are all exposures
of DPE=19 and longer.  The diamonds include DPE=11 exposures and are
plotted with expanded time scale in the bottom panel.  Yohkoh night is
also displayed in the bottom panel

Until further notice we will assume a failure time of

	20-APR-99  19:02:00

and a failure fraction of 1/12 or 0.0833 for this failure event.

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