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Effect of Ent.-Filter Correction on SXT Temperatures

Image name: Te_Effect_of_Ent_Filt_Changes.png (click image to enlarge)
Image size: 10.2870 KB (1024x512)
Date submitted: 18-Jan-1996


As part of a study of solar cycle effects and the sun as a star I've derived
the gross average coronal temperature for 12,208 AlMg/Al.1 SFD image pairs
which were taken within 3 minutes of each other over the period

	(first, last) = '10-NOV-91  15:21:01', '11-NOV-95  13:55:36'.

Of these pairs of images 3197 were acquired before the first entrance filter
failure on 13-NOV-92 16:50, 8507 between the first and second entrance
failure, and 504 after the second entrance filter failure on 16-AUG-95 08:21. 

This figure illustrates the magnitude of the correction to derived
temperature as a function of the date-corrected temperature.  The LH plot
displays the temperature difference and the RH plot displays the temperature
ratio.  The lower curve in each plot is for the 8507 cases between the first
and second failures and the upper curve is for the 504 cases after the second
failure.  It is clear that the correction is significant -- and quite
temperature dependent.  The date-corrected temperature is higher than if the
change in entrance filter transmission is ignored. 

However, I must emphasize that our knowledge of the "open fraction" of the
entrance filter is poor.  The values in the SXT data base, used here, are
0.0833 and 0.1667.  These have been estimated from the straylight -- and are
only approximate.  I believe that the FFI "starburst" images may be helpful
in deriving a more accurate estimate.  Changes in the azimuthal distribution
of scattered x-rays were clearly evident following the second failure. 

                                        L. Acton  18-Jan-96

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