SXT Status Report 4 April 1997 to 21 April 1997 (Weeks 14-16) Hugh Hudson SUMMARY SXT continued to operate well. Solar activity was generally low but yielded two Yohkoh flare-mode triggers on April 15. SOLAR ACTIVITY Activity was low throughout weeks 15 and 16, with the exception of the two C-class flares causing Yohkoh flare-mode flags on 15 April. These flares were from two new-cycle regions, and the new-cycle regions seem to be dominating the activity now. The general pattern seems to be hot start => short lifetime. A remarkable phenomeon occurred at the boundary of the N polar hole on 10-11 April. Possibly this was just a peculiar "restructuring" as a part of the normal helmet-streamer evolution, but it sure looked different. Fans of boundary behavior in coronal holes, and there are many such scholars around the world, might want to take a special look at this. SXT INSTRUMENT STATUS SXT continues to perform well technically. One of the two flare flags did not result in correct ARS function, but the reason for this (stray light in the Be filter used for flare ARS patrol images) was recognized and corrected. A second flare with the old setting had shown correct behavior before the fix was in place. The current flare-mode observational sequence emphasizes ejecta, and the second flare on 15-Apr was one of the few chances we have had to test this sequence. It looks good but there was no beautiful ejection to observe. SXT CALIBRATION ACTIVITIES Thanks to Lemen's software improvements on his last visit, the terminator program is on a much solider footing. The Yohkoh pointing was adjusted (S/C south by about 1 arc min) to allow for the seasonal drift of the attitude control system. The previous adjustment had been made December. The behavior is quite regular, so another adjustment will probably be made in six weeks or so; by doing this we keep a tighter pattern of terminator image locations relative to the real observations and can do more accurate corrections. This is mostly for the sake of the Al.1 filter, which has a complicated stray-light pattern. PASS CONFLICTS Yohkoh loses some KSC real-time telemetry passes to other spacecraft; ISAS now has the new radio astronomy mission (HALCA) as well as others. During the setup activities for HALCA, which continue, we will be losing contact passes frequently as shown below. However from Week 17 the number of losses will decrease. A few other passes were lost to ASCA and AKEBONO, but the ASCA conflicts have almost disappeared now due to orbital precession. Week 14: 12 passes were canceled for HALCA Week 15: 10 passes were canceled for HALCA Week 16: 8 passes were canceled for HALCA. CAMPAIGNS There were no organized campaigns during this interval. For Yohkoh target planning, the SXT weekly observing plan is available on the Web at http://www.space.lockheed.com/SXT/html2/First_Light.html or with "finger campaign@isass0.solar.isas.ac.jp | more" . See http://sohowww.nascom.nasa.gov/operations/targets/today" for SoHO target planning. VISITORS AND PERSONNEL Loren Acton departed, but will return in May for the Solar-B meeting and some research. Serge Savy left for the Aussois meeting on filaments. Hugh Hudson returned from Australia. SEMINARS There was a double Yohkoh seminar on April 17: C. Foley (UC London/MSSL) "Scattering Characteristics of Yohkoh SXT" H. Hudson (SPRC/ISAS) "Interactions of Coronal Currents: Helicity Twitching and Sloshing?" (journal review) This was well-attended. Both talks caused lots of discussion, and in the helicity talk a bit of confusion. Nobody asked about "twitching and sloshing", so there will be another go at this most likely. The new work on the SXT point response function (Foley and Shin) seem extremely likely to put the SXT scattering function a firmer foundation, so we expect that many of the measurements will improve considerably. TOHBANS Tohbans for Week 14: SSOC : S. Tsuneta & S. Savy KSC : M. Shimojo & S.Kubo SXT_CO: L. Acton SXT_SW: - Tohbans for Week 15: SSOC : Y. Saito & S. Yashiro KSC : M. Shimojo & M. Yamamoto SXT_CO: L. Acton SXT_SW: - Tohbans for Week 16: SSOC : J. I. Khan & D. Alexander KSC : M. Yamamoto & S. Tanuma SXT_CO: H. Hudson SXT_SW: - QUOTATION "A Nobel Prize in Physics and I'm fighting to keep my diaper on". Dr. Sam Beckett, Quantum Leap.