Report from ISAS 12 September - 18 September, 1994 Marilyn Bruner SUMMARY This week was dominated by the SPARTAN operation. Bruner and Hudson worked together on analyzing the SXT data taken during the previous rotation and kept the SPARTAN team advised of the current state of the sun and its probable evolution. The SXT observations went very well, with one minor "learning experience" about the operation of the ARS patrol. The sun remained very quiet throughout the period. A systematic program to accumulate terminator images at various spacecraft offpoint values has been started. OPERATIONS This week's operation went very, very well. The HXT "spectroscopy" mode test was discontinued in favor of the SPARTAN campaign, as planned. The operation was dominated by the needs of the SPARTAN campaign and all the hard work that had been done in preparation bore fruit. All of the SXT advisory and observational goals were achieved. The SPARTAN was deployed with the full benefit of the latest information about the state of the corona. The SXT data taken during the campaign are of excellent quality. A great deal of credit should be given to the Tohbans, T. Matsuda and S. Sano at KSC and A. Okubo and M. Ohyama at the SSOC. They worked very hard, and were able to react quickly to unexpected events and changes in the observing plan. One SXT error was discovered on Pass 1 on Monday. The Tohbans reloaded the SXT-U microcomputer and successfully restored the SXT to normal operation by the end of Pass 2. SXT Observers Bruner and Hudson received an unscheduled lesson on the operation of the Active Region Selection system (ARS) when observations were shifted to the South 16' offpoint. At this orientation, the usual ARS1 will not find active regions located on or north of the solar equator because they fall above the area on the CCD that is normally searched. In order to make ARS1 work under these conditions, it is necessary to change the Common Table parameters R1S and R1S from 72 to 100. This moves the region scanned by the ARS system up toward the top of the CCD, where the equatorial active regions are located when the spacecraft is shifted to South (16'). The SXT Table Loading Software (SXTSPT) rejects higher values, which caused some initial confusion while the new tables were being prepared. One must remember to restore these parameters to their normal value of 72 at the conclusion of South (16') offpoint observing. Finally, we have began a systematic background observing program to acquire terminator images to evaluate the stray visible light pattern seen at each of the S/C offpoint orientations that are normally used during Yohkoh operations. These data are especially important now that the SPARTAN campaign has been successfully concluded. Since most of these data were taken with the spacecraft pointed away from the normal position, the terminator data are needed to correct the observations for stray visible light. The most critical images, for the thin aluminum filter, have been recorded at least once at each offset location. A few have been recorded twice. In the next two weeks, it is important to complete the set for the AlMg and Mg3 filters, so that they will be from the same epoch as the prime campaign data. A special form has been prepared for recording these observations, and Hudson has generated a procedure to be followed. The method is simple; the pointing and return commands together with "Control Manual" and "Control Auto" commands to re-start the SXT observing table, are inserted into the OP table that is loaded into the spacecraft each day. The Chief Observer should make certain that the desired filter is called up in entry number 1 of the Quiet High FFI table that will be used. The OP First Guess program will identify candidate terminator observing times for assistance in planning. SOLAR ACTIVITY Solar activity continued at a very low level throughout the week, hovering around the A1 level for most of the period. Active regions 7773, 7774 and 7776 continued to fade, and had disappeared behind the West limb by the end of the week. The loop system at the S-W limb continued to expand, and looked very much like the base of a large helmet streamer at the time of the SPARTAN observations of that location. There was also a considerable amount of loop structure above the west limb at that time, due to the active regions that were just beyond it. The North polar coronal was well developed at the time of the SPARTAN observations, though the limb was backlit by coronal material above the North polar crown filament channel on the far side of the sun. This was in accordance with predictions passed to the SPARTAN team by the SXT team. The presence of this activity, however, does not rule out the possible existence of open field lines above the pole and nearby regions. PERSONNEL Marilyn Bruner continues to serve as SXT Chief Observer. Jean-Pierre Wuelser continues to share the duties of table generation, and will take over as Chief Observer next week, when Bruner returns to California. Hudson departed on Friday for a two week stay in the US. Freeland arrived, ending the programmer drought that has afflicted us since the departure of Linford in late August. Lemen is expected to arrive about September 26th to assume the duties of SXT Chief Observer. SCIENCE Hudson continued his work on the review article with Ryan, when not otherwise occupied with the SPARTAN campaign. Wuelser continued to study the questions of co-alignment and the effective angular size of the SXT pixels. PLANS Next week's operation is expected to be more benign. We will continue to observe the development of the regions that were observed during this week's campaign, as requested by the SPARTAN team. 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.