SXT OPERATIONS STATUS REPORT FOR WEEK ENDING 29 FEB 1992 -------------------------------------------------------- OPERATIONS ---------- After 6 months in orbit the Yohkoh mission continues to gather new and exciting data on the Sun. Apart from a bit-map error early on Sunday morning which was corrected and did not stop observations, the SXT has continued to work smoothly in the last week. The Sun has been relatively quiet but has produced two very large flares: 1) An M4 long duration event that occured on the east limb at about 03:00 UT on 21 February 1992 and lasted for at least 9 hours. It had a spectacular "helmet" structure which grew steadily throughout this time. The SXT obtained an excellent series of pre-flare, flare, and post-flare images both in PFI and FFI mode. Greg Slater and Keith Strong have been working to make this into a co-registered movie so the dynamics of the event can be studied more easily. Bob Bentley has produced a S XV BCS spectral movie of the same event showing a lightcurve, spectrum, and SXT PFI image simultaneously. While looking like a classic Kopp-Pneuman flare there are several aspects of the SXT data form this and similar events that may make us rethink this simple picture. 2) An X3 long duration event occured from the same region near disk center at about 10:00 UT on 27 February 1992. It occured as the Yohkoh came out of night but was still in SAA. As we did not go into flare mode as none of the Yohkoh flare flags were operating as the other instruments were off only SXT observed the onset of the event. Unfortunately most of the FFI's are too badly saturated to produce and useful data but some of the PFI's are usable. The long series of FFIs and PFI's in this extemely bright event have produce a small blemish on the optical and diffuser images which is being investigated currently. Keith Strong and Nariaki Nitta investigated in detail the origins of the previous series of such optical blemishes on the CCD. The theory that these were also due to SAA operations was shown to be incorrect and mostly could be traced back to an SEU event that caused a hard reset of the SXT in early February. However, we should have enough data now on these optical blemishes to accurately assess the X-ray exposure needed to produce a blemish of a given depth and so evaluate the risks and benifits of particular modes of operations. Dick Canfield completed his report on the X-ray sensitivity of SXT and concluded that within a few percent it has remained constant throughout the last 3 months. He has volunteered to continue this study after returning to Hawaii and extend it to a lower-energy channel (only used Be filter so far) and continue to update the plots as new events become available. At the monday Ops meeting, chaired by Kosugi-san, we heard that the KSC 20M antenna drive broke and that could inhibit operations but it was quickly fixed and little or no data was lost. Hugh Hudson gave an impressive report on his work on coalignment between HXA and SXT showing that a simple correlation existed that was good to a few arcsec. However there were obvious slowly varying components, which could be related to the temperature of the instrument support plates, that if removed, in principal, could refine the pointing to a sub arcsec level. This combined with IRU output should enable us to produce relative and absolute pointing coordinates more than adequate for scientific purposes. Greg Slater and Keith Strong then used some of Hugh's IDL routines to reregister the SXT Novemeber full-frame movie with excellent results except where the HXA fiducials obscured the limb due to a large offpoint to the south requested by BCS. SCIENCE PROGRESS ---------------- J-P Weulser and Dick Canfield have continued to work on the 15 November flare by adding new combinations of H-alpha, magnetogram, SXT, and HXT images. Greg Slater has recorded this on the optical disk and produced a video tape of it. A large number of new science topics have been added to the Yohkoh Team Bullatin board recently, mainly due to the influx of visitors from the BCS team who have stimulated many interesting ideas and looked at a huge amount of data that was previously unexplored. We now have over 90 scientific investigations that are outlined on the TBB. Uchida-san and Keith Strong discussed how to improve the scientific coordination between the Japanese community, the resident scientists at ISAS, and the short term visitors. We have also discussed the PASJ inputs, the deadline for which just past. PERSONNEL --------- Ken Phillips, Uri Feldman, Hugh Hudson and Dick Canfield left this week. Andrew Phillips arrived from MSSL to join the BCS team. Mons Morrison arrived from Palo Alto and is already working on rearranging the data on the data disks in preparation for the start of regular data archiving. Nariaki Nitta and Greg Slater return to Palo Alto during this coming week. On Friday we had a film crew visit us to record some of the recent data for a short history of the construction, launch, and operations of Yohkoh. On the same day two visitors from the British Embassy visited ISAS and came to see the Yohkoh data. Keith Strong 2 Mar 1992