SXT REPORT FOR WEEK 20; 9 MAY 1993 TO 15 MAY 1993

GENERAL STATUS

          Sxt continued to work well this week.  Last week's 
     collaborative observations were completed over the weekend.  We 
     continued observations of NOAA active regions 7496 and 7500 as they 
     crossed the limb.  Since they were the dominant features, we decided 
     to track them by dead reckoning with ARS disabled.  The operation was 
     very successful, and the data are of excellent quality.  An M flare 
     was observed by Yohkoh on 14 May, and there were numerous C flares.


PERSONNEL
     
          Mons Morrison arrived for a 3 month tour.  Marilyn Bruner took 
     over the SXT Chief Observer duties from Hugh Hudson.  Gerry Doyle 
from the Armagh observatory arrived for a two week visit.  He 
will be working primarily with the BCS team, but will also work 
with Hudson in comparing SXT and BCS flare data.

SOLAR ACTIVITY

          The active region pair NOAA 7496 and 7500 were the dominant 
     features on the disk for the whole week.  An interesting discovery 
     by Labonte and Bruner was a dark lane between the two regions 
     underneath of which could be seen bright plage material in H-alpha 
     images.  This observation is surprising, since conventional wisdom is 
     that plage regions are correlated with footpoints of overlying x-ray 
     coronal loops.  A TBB item will be submitted to study these data.  
     The M flare appeared late in the week in AR 7500; a delta region that 
     was known to have the capacity to produce a substantial flare.

SCIENCE PROGRESS

          Hudson has completed the manuscript for the Nature paper on 
     which he and Strong are co-authors.

SXT OPERATIONS

          Initial attempts to observe the dual active regions 7496 and 
     7500 with ARS-2 were frustrating, as the bright one would be 
     centered, and the other would be out of the field of view.  We 
     decided to observe them with a 1 x 4 ROI with ARS disabled and to 
     manually set the position of the ROI each day, based on the location 
     of the AR's on the previous day.  The idea was to make the ROI a bit 
     longer than necessary and to allow solar rotation to carry the active 
     regions slowly through the field during the course of the day.  The 
     first attempts to do this were carried out manually, using the 
     `profiles' utility to locate the desired pixel coordinates.  Sam 
     Freeland created a utility that places an ROI-sized box on a full 
     frame image such that it can be positioned with the mouse.  The 
     function, ORCENT, returns a 2 element vector containing the macro-
     pixel coordinates in the form for direct entry into the ROI table.  
     With this new tool, manual selection of the SXT field of view is 
     rapid, simple, and reliable.  We hit the desired target on every 
     attempt.

          Freeland's major effort for the week was the installation of a 
     system to automatically update Yohkoh software on all of the 
     workstations participating in the mission, including those at remote 
     sites.  Once this system is checked out, it will ensure that all 
     sites are using the same (and latest) versions of the analysis 
     software.

          Plans were made late in the week for an observing campaign with 
     Big Bear, Kitt Peak, and Mees observatories for a study of X-ray 
     bright points.  The campaign will begin on Monday, 17 May.  Initial 
     studies will use the FFI dominant mode.  PFI dominant mode may be 
     tried later in the week, if studies of the problems encountered in 
     the last use of this mode can be understood and corrected.


                                             Marilyn Bruner
                                             SXT Chief Observer