Report from ISAS 5 September - 11 September, 1994 Marilyn Bruner SUMMARY Solar Activity has steadily decreased during the week, and had dropped below GOES B-1 level by late Saturday. AR 7773 continued to be the dominant source of activity for most of the period though regions 7774 and 7776 were also observed on occasion. Much of the effort has been devoted to preparing for the SPARTAN mission, which was launched on the Shuttle Endeavor a few hours ago. OPERATIONS This week's operation again went very smoothly. The HXT "spectroscopy" mode test has continued, and several C class flares have been observed by now. We have confirmed that the SXT partial frame images are suppressed for an interval following the flare, when the spacecraft telemetry rate shifts from Flare High to Flare Medium. The special mode ends upon the next entry to either the South Atlantic Anomaly or the next night period. It is intended to return the HXT to normal mode during the SPARTAN operation, so that any flares occurring during the period will not have an impact on support of the SPARTAN and Ulysses missions. Most of our activity has centered around preparing an observing table suitable for co-observing with the SPARTAN and Ulysses missions. The low level of activity on the disk has permitted us to use exposures as long as 1 minute without substantial saturation effects. SPARTAN support observations will include long and medium exposures in the AlMg, Al1 and MG3 filters, as well as the standard movie exposure sequences. The sequence timing is such that two complete filter sequences can be completed in each daylight orbit whenever Yohkoh is operating in the Quiet High mode. Part of our SPARTAN support has included preparing briefings to the SPARTAN investigator team on the state of the sun during both the last few days before deployment and during the previous rotation. Materials have included E-mail and Fax messages, Faxes of X-ray contour maps, and specially prepared images available via anonymous ftp. SOLAR ACTIVITY Active region 7773 has gradually faded in x-rays as it crossed the solar disk, and the other regions that have appeared are also relatively benign. Only C class and smaller events have been observed during the week. Attention has shifted to large scale structures above the limb, in preparation for SPARTAN. Late today, we observed a very large loop structure expanding above the S-W limb. It's appearance and motion are very suggestive of CME's seen in white light. It will be interesting to see whether this event continues to develop over the next several hours. So far, it has not been possible to identify prominent helmet streamer activity, though some cusp-shaped loops were observed earlier in the week. The filament channel that was observed late last week is passing the W limb at the moment, and substantial x-ray emission can be seen above this part of the limb. The polar crown filament channel is still visible in x-rays, and the pole is obscured by intervening material. The North pole is covered by a well-defined coronal hole above latitude 70 N. PERSONNEL Marilyn Bruner continues to serve as SXT Chief Observer. Jean-Pierre Wuelser has begun a refresher course in this activity so that he can serve during the one-week interval between Bruner's departure and Lemen's arrival for his next tour. SCIENCE Several studies involving comparisons of meter-wave data with SXT data are under way. Wuelser arrived with a list of type II events; Hudson is still plugging away on the lists left by Gopalswamy and Kundu; the Masuda list is full of meter-wave correlations, some of which fall in the Nancay time frame, and there is some overlap with "flare nimbus" events being studied by Don Neidig and others. In view of the success with fast-drift bursts (U and III, Pick and Raulin, respectively) not related to major flares, and in view of Shibata's discovery of ejecta in all of the Masuda events, this is a very promising line to pursue. Hudson is collaborating with Jim Ryan (U.N.H.) on a review of "Energetic Particles in Solar Flares". This is happening at just the wrong time because of the huge interest being shown in the loop-top impulsive hard X-ray sources! We hope that at least some of the literature makes the cutoff date for the review. Nishio, Kosugi, Hudson and Wuelser have been analyzing the Mercury transit observations of SXT. In the course of this work Wuelser uncovered a problem in the SXT suncenter locations that are used in the Yohkoh analysis software. This problem affects all co-alignment work of recent Yohkoh data with ground-based observations. Starting in spring 1993 the software introduced an ever-increasing error in the N-S direction (the software reports suncenter too far South on the SXT detector). The error was initially small but has now grown to 15 arcseconds for September 1994 data. Wuelser found the problem in the hxa_suncenter program and related software, based upon use of the archive of X-ray suncenter locations that is automatically generated, courtesy of Mons Morrison. He is now re-analyzing the relationship between the HXA aspect sensor and the SXT coordinate system for the entire mission. The goal is to correct the error and improve the pointing solution to sub-pixel accuracy. We will distribute another message as soon as the problem is fixed. PLANS Next week's operation will be dominated by the SPARTAN / Ulysses support operation. We have received a preliminary time-line for the Shuttle operations; it is very favorable for coverage by both KSC and DSN passes. A major scientific objective of the SXT observations is to determine the coronal structure in the intermediate region above which ground-based observations become difficult and below the inner radial limit of the SPARTAN instruments. The filter selection is optimized to give us the best possible dataset for determination of both the morphology and the plasma properties of the coronal material. We would like to learn both how far above the limb our diagnostics may be used, and how they compare with the results of the two coronagraph experiments on SPARTAN 201-2.